© 2019, The Author(s). Optical rectennas are expected to be applied as power sources for energy harvesting because they can convert a wide range of electromagnetic waves, from visible light to infrared. The critical element in these systems is a diode, which can respond to the changes in electrical polarity in the optical frequency. By considering trade-off relationship between current density and asymmetry of IV characteristic, we reveal the efficiency limitations of MIM diodes for the optical rectenna and suggest a novel tunnel diode using a double insulator with an oxygen-non-stoichiometry controlled homointerface structure (MOx/MOx−y). A double-insulator diode composed of Pt/TiO2/TiO1.4/Ti, in which a natural oxide layer of TiO1.4 is formed by annealing under atmosphere. The diode has as high-current-density of 4.6 × 106 A/m2, which is 400 times higher than the theoretical one obtained using Pt/TiO2/Ti MIM diodes. In addition, a high-asymmetry of 7.3 is realized simultaneously. These are expected to increase the optical rectenna efficiency by more than 1,000 times, compared to the state-of-the art system. Further, by optimizing the thickness of the double insulator layer, it is demonstrated that this diode can attain a current density of 108 A/m2 and asymmetry of 9.0, which are expected to increase the optical rectenna efficiency by 10,000.

© The Electrochemical Society. In this study, Cr-poisoning in a SOFC mixed conducting cathode was investigated. To examine the influence of the electrode reaction systematically, a model patterned thin film electrode was used. La0.6Sr0.4CoO3-δ was chosen as the model cathode material. The LSC model electrode was exposed to Cr-containing oxygen at 973 K under a cathodic polarization. The Cr content in the feed gas was controlled by setting the temperature of a Cr-source at 973 K or 773 K. The degradation of the electrode performance was observed under both conditions. Deposits observed on the electrode surface were SrCrO4 for the higher Cr-concentration in the feed gas. On the other hand, deposits were Sr-compounds without detectable amount of Cr for the lower Cr-concentration. These results may indicate that not only the Cr-deposition but also the decomposition of the electrode material could be considerable causes for the Cr-poisoning in mixed conducting cathodes depending on the Cr-concentration.

Chapter12-Sessions B14,B15-51/169

Chapter08-Sessions B03,B06-77/169

Chapter08-Sessions B03,B06-68/169

© 2018 Elsevier Ltd The thermal stability of spectrally selective few-layer metallo-dielectric structures is evaluated to analyze their potential as absorber and emitter materials in solar thermophotovoltaic (STPV) systems. High-efficiency (e.g., STPV) systems require materials with spectrally selective properties, especially at high temperatures (>1273 K). Aiming to develop such materials for high-temperature applications, we propose a few-layer structure composed of a refractory metal (i.e., Mo) nanometric film sandwiched between the layers of a dielectric material (i.e., hafnium oxide, HfO2) deposited on a Mo bulk substrate. In vacuum conditions (<5 × 10–2 Pa), the few-layer structure shows thermal stability at 1423 K for at least 1 h. At 1473 K, the spectral selectivity was degraded. This could have been caused by the oxidation of the Mo thin film by the residual oxygen through the grain boundaries of the upper HfO2 layer. This experiment showed the potential stability of few-layer structures for applications working at temperatures greater than 1273 K as well as the degradation mechanism of the few-layer structure. This characteristic is expected to help improve the thermal stability in few-layer structures further.

We numerically investigate radiative heat transfer enhancement using spectral and geometric control of the absorber/emitter. A high extraction of the radiative heat transfer from the emitter as well as minimization of the optical losses from the absorber leads to high extraction and solar thermophotovoltaic (STPV) system efficiency. The important points for high-efficiency STPV design are discussed for the low and high area ratio of the absorber/emitter. The obtained general guideline will support the design of various types of STPV systems.

Easy-to-fabricate, high-temperature, thermally-stable radiators are critical elements for developing e cient and sustainable thermophotovoltaic energy conversion devices. In this frame, a trilayer-on-substrate structure is selected. It is composed of a refractory metal - molybdenum - constituting the substrate and an intermediate thin film sandwiched between two hafnia transparent layers. An in-depth analysis shows that two spectrally distinct interference regimes take place in the hafnia layer-molybdenum thin film substructure, and that backward and forward thermally-emitted waves by the thin film are selected in two distinct interferential resonating cavities. The interference regimes within and between these cavities are key to the spectral shaping of thermal emission. The radiative performances of the structures are evaluated by introducing a figure of merit. Using the example of a GaSb cell, it is shown that the structure can be optimized for providing the broadband large emission with a steep cuto required for mitigating photoconversion losses.

© 2018 International Heat Transfer Conference. All rights reserved. Making periodically aligned microstructures with sub-micron size on a refractory metal is one of the promising technologies of increasing solar absorption selectively at high-temperature condition. However, the technique of fabricating microstructures for refractory metal is limited, such as using semiconductor technologies. Therefore, the large-area fabrication of microstructures on refractory metals is a key technology supporting the practical application of controlling optical property using surface microstructures. This report describes large-area fabrication of two-dimensional submicron quasi-periodic microstructures using spinodal decomposition on a nickel-based superalloy. The surface microstructures were obtained only by appropriate heat treatments and simple chemical etching process. The size of microstructure; i.e. depth, width, can be controlled with heat treatment conditions and etching time. Solar selective absorptance of 0.82 and hemispherical total emittance of 0.31 at 600oC can be obtained with the proper treatments.

We present a comprehensive approach for tailoring the spectral and angular properties of infrared thermal radiation by using a polymer resonator with molecular vibrational modes, consisting of a polymer thin film on a back-reflective substrate. To precisely design the resonator, we derived the infrared dielectric function of a poly(methyl methacrylate) (PMMA) thin film from the measured reflectance spectrum by fitting it with a Gaussian-convoluted Drude-Lorentz model while accounting for the inhomogeneous broadening caused by the disordered structure of polymers. Our experimental and numerical characterization confirms that the polymer resonator exhibits spectral shaping from quasi-broadband to narrowband due to the intrinsic molecular vibrational absorption of the polymer. The frequency-isolated and strong molecular vibrational absorption of the carbonyl stretching mode at 1730 cm−1 enables the narrowband shaping of the PMMA resonator. In addition, we confirm that the angular-shaping characteristics of this polymer resonator can be tuned, from omnidirectional to strongly angular selective, by changing its polymer film thickness. Modal dispersion analysis reveals that the angle-selectivity of the polymer resonator at an angle of incidence of 80° comes from coupling between the molecular vibrational mode and leaky mode. The proposed infrared radiation management strategy based on molecular vibrational modes of polymers is cost-effective, scalable, and works well with terrestrial matter, including organic compounds and gas molecules, showing promise for applications such as optical gas sensing and radiative thermal management.

Radiative cooling accomplished by tailoring the properties of spectral thermal emission is an interesting method for energy harvesting and high-efficiency passive cooling of terrestrial structures. This strategy, however, has not been extended to cool enclosed heat sources, common in engineering applications, and heat sources in high-temperature environments where radiative transfer plays a dominant role. Here we show a radiative cooling scheme for a high-temperature gaseous medium, using radiative heat extraction with selective absorbers matched to the gas-selective emission properties. We used SF6 gas plasma as a model, because this gas is used in gas circuit breakers, which require effective cooling of the hot insulating gas. Our theoretical analysis confirms that a copper photonic absorber, matched to the ultraviolet-to-near-infrared-selective emission properties of the gas, effectively extracts heat from the high-temperature gas plasma and lowers the radiative equilibrium gas temperature by up to 1270 K, exceeding both blackbody-like and metallic surfaces in practical operating conditions.

A small power source was designed based on a liquid hydrocarbon fueled micro-SOFC. In order to achieve thermal insulation in a restricted volume, a vacuum thermal insulator was developed and tested it revealed that even a 1 mm vacuum zone showed high thermal resistivity over 200 KW-1 at 300°C. Internal reforming tests with methanol-based fuels were performed with an isolated micro reformer the results suggested that sufficient amount of methanol could be reformed at 400°C. Finally, an integrated system of thermal insulator, reformer, and micro-SOFC was tested to prove the feasibility of the design, which was expected to achieve higher energy density per volume/mass than Li-ion batteries.

Cr-poisoning at an SOFC cathode was investigated by using the patterned thin film model electrode of La0.6Sr0.4CoO3-δ on a Ce0.9Gd0.1O1.95 electrolyte. The model electrode was exposed to Cr-containing oxygen gas for a week at 973 K while applying the cathodic bias. After the Cr-poisoning test, the surface morphology and the distribution of Cr were examined by means of SEM and SIMS. Deposition of Cr-containing particles was observed on the electrode surface preferentially near the electrode/electrolyte interface. This result demonstrated that the cathodic polarization accelerated the Cr deposition especially at the area where the cathodic reaction took place.

The cathodic reaction of a solid oxide fuel cell (SOFC) was investigated by 18O/16O isotope exchange with/without polarization and isotopic distribution analysis by second ion mass spectroscopy. In order to elucidate the contribution of triple phase boundary (TPB) reaction while eliminating the influence of the electrode microstructure, a patterned thin film electrode was used as a model cathode. La0.6Sr0.4CoO3-δ was chosen as a model material exhibiting mixed ionic and electronic conduction. A slight increase in the 18O ratio was observed within 20 μm from the electrode/electrolyte interface under a constant cathodic polarization of 220 mV at 973 K in 1 bar of P(O2). Such an increase in the 18O ratio was considered to be caused by the electrochemical oxygen incorporation. The contribution of the TPB reaction to the total cathode reaction was not clearly observed at least in applied experimental conditions.

Long-term reliability and durability are of great importance for the commercialization of SOFCs. Mechanical behaviors of ceramic components, including cell fracture, are necessary to be understood in order to ensure stability of SOFCs. For the multiscale simulation of the thermo-chemo-mechanical behavior, various related materials properties are indispensable. This paper reports the evaluation procedure of material properties for comprehensive analysis of chemically- and thermally induced mechanical behavior of SOFCs.

A spectrally selective absorber composed of a monolayer transparent conductive oxide (TCO) coated on a metal substrate is investigated for use in solar systems operating at temperatures higher (>973K) than the operation temperature of conventional systems (similar to 673 K). This method is different from the currently used solar-selective coating technologies, such as those using multilayered and cermet materials. The spectral selective absorption property can be attributed to the inherent optical property of TCO owing to the plasma frequency and interferences between the substrates. Since spectral selectivity can be achieved using monolayered materials, the effect of atomic diffusion occurring at each layer boundary in a multilayer or cermet coatings under hightemperature conditions can be reduced. In addition, since this property is attributed to the inherent property of TCO, the precise control of the layer thickness can be omitted if the layer is sufficiently thick (>0.5 mu m). The optimum TCO properties, namely, carrier density and mobility, required for solar-selective absorbers are analyzed to determine the cutoff wavelength and emittance in the infrared range. A solar absorptance of 0.95 and hemispherical emittance of 0.10 at 973K are needed for achieving the optimum TCO properties, i.e., a carrier density of 5.5 x 10(20) cm(-3) and mobility of 90 cm(2) V-1 s(-1) are required. Optical simulations indicate that the spectrally selective absorption weakly depends on the incident angle and film thickness. The thermal stability of the fabricated absorber treated at temperatures up to 973K for 10 h is verified in vacuum by introducing a SiO2 interlayer, which plays an important role as a diffusion barrier. Published by AIP Publishing.

A feasible study for an in-situ stress evaluation method for solid oxide fuel cells based on Raman scattering spectroscopy was performed using two anode-supported cells with a cathode interlayer made from Samarium (Sm) doped ceria. Model cells with a dense cathode interlayer demonstrated a compressive stress of -100s MPa at room temperature, and the results were comparable to those from X-ray diffraction. Model cells with a porous interlayer showed complex stress conditions that deviated from in-plane stress due to their porosity, and the model cell was confirmed not to be suitable for this method. At high temperatures, compressive stress was found to decrease as temperature increased and was almost neutral at the operating temperatures of the fuel cell, with good replication. Hence, the feasibility of this method for model cells with a dense cathode interlayer was confirmed. (C) 2017 The Ceramic Society of Japan. All rights reserved.

Passive thermal management has attracted much attention for use in electronic devices. In this study, we propose a novel thermal management technique based on spectral matching between thermal radiation and the infrared optical window of polymers, which are widely used in device encapsulation and packaging. The unique effects of this technique on heat transfer were numerically and experimentally studied. Our numerical analysis confirms that selectively enhancing thermal radiation in the optical window of polymers improved thermal propagation deep into the polymers, reducing local temperature distributions at their surface. In addition, our experiments demonstrate that boosting thermal radiation propagation deep into polymers effectively enhanced their heat spreading and dissipation. Our new method for thermal management in polymers can improve passive thermal management in electronic devices that include polymers. (C) 2016 Elsevier Ltd. All rights reserved.

The contribution of the triple phase boundary reaction in a mixed ionic and electronic conducting (MIEC) cathode in solid oxide fuel cells (SOFCs) was investigated. For this purpose, patterned thin film electrodes with or without triple phase boundaries, which simplified the microstructure of a practical porous electrode, were proposed and fabricated. In this work, an La0.6Sr0.4CoO3-delta (LSC) electrode on a Ce0.9Gd0.1O1.95 electrolyte was chosen as a model SOFC MIEC cathode. Effective reaction area was evaluated by means of operando micro X-ray absorption spectroscopy with the model electrodes under 10(-2) bar of p(O-2) at 873 K. It was found that the introduction of triple phase boundaries shortened the effective reaction area. The results may indicate the non-negligible contribution of the triple phase boundary reaction even in SOFC MIEC cathodes.

Solar selective absorbers that function at temperatures up to 700°C and possess shallow honeycomb cylindrical microcavities coated with a metal-dielectric multi-layer are investigated. Even shallow microcavities, absorptance at solar spectrum range is largely increased due to multilayer showing spectrally selective absorption property. To obtain high spectral selective property, design strategy for the multilayer coated microstructure is established. Honeycomb array cylindrical microcavities were fabricated on tungsten substrate and multi-layers consisting of platinum nano-film sandwiched by aluminum oxide layers were created for a uniform coating via atomic layer deposition. Thermal stability of the fabricated sample at 700oC in vacuum is verified through annealing test for 100 h.

A transparent conductive oxide (TCO) film coated metal microstructures as solar selective absorbers for high-temperature usage exceeding 700 degrees C is introduced. Steep absorption cutoff property and low-emittance at infrared range owing to TCO characteristic can be seen, whereas high-absorptance explained by interaction of incident light and microstructures of which size is submicron is appeared. Honeycomb array cylindrical microcavity of which an absorptance peak appeared at around 0.8 mu m was fabricated on a tungsten (W) surface with interference lithography technique. The fabricated sample consist of 1.0 mu m indium tin oxide film and W microstructure showed solar absorptance alpha(s) = 0.83, hemispherical emittance epsilon(ht)= 0.16 assuming the absorber temperature at 700 degrees C, and performance factor eta = 0.76. Short duration thermal stability was confirmed at 700 degrees C for 2 h in vacuum condition.

A high-efficiency solar thermophotovoltaic (STPV) system has been demonstrated using spectrally selective planar absorber/emitter systems and a GaSb TPV cell. In this study, a novel approach for designing the STPV system based on the efficiency of unidirectional radiative heat transfer has been introduced. To achieve high extraction and photovoltaic conversion efficiencies, the spectrally selective absorber/emitter based on a coherent perfect absorber composed of a thin molybdenum layer sandwiched between hafnium layers was applied. The extraction efficiency was further investigated with respect to the absorber/emitter area ratio. The experimental efficiency of STPV reached 5.1% with the area ratio of 2.3. (C) 2016 The Japan Society of Applied Physics

Regarding the fabrication of solar selective absorbers, the ability to create microstructures on top of metal surfaces is a promising technology. Typically, these materials are able to possess spectrally-selective absorption properties for high-temperature usage. Solar-selective absorbers that function at temperatures up to 700 °C and possess shallow honeycomb cylindrical microcavities coated with a metal-dielectric multi-layer have been investigated. Honeycomb array cylindrical microcavities were fabricated on W substrate with interference lithography and multi-layers consisting of Pt nano-film sandwiched by Al2O3 layers were created for a uniform coating via atomic layer deposition. The absorbance spectrum of fabricated samples reveals results consistent with a simulation based on a rigorous coupled-wave analysis method. A solar absorbance value of 0.92 and a hemispherical total emittance value of 0.18 at 700 °C was determined from the fabricated solar-selective absorber. Additionally, thermal stability of up to 700 °C was confirmed in vacuum.

Solar-thermophotovoltaic system is expected to have high efficiency by converting wide spectral range solar energy into useful thermal radiation energy. However, the experimental STPV system shows much lower efficiency than theoretical one. To achieve high-efficiency, it is essential to obtain good spectrally matching between thermal radiation spectrum and PV cells spectral response. In this paper, the power generation tests using the whole configuration of the STPV system is described. The conversion efficiency of GaSb PV cell is estimated to be 20 to 23% against to the light intensity irradiated on the PV cell surface. The net system efficiency of 1.9% can be achieved. The application of thermal storage system to the STPV is also considered.

© 2016 by ASME. The spectrally selective coating technology which can be applicable for solar-thermophotovoltaic (solar-TPV) generation systems is described in this paper. In solar-TPV system, the spectrally selective absorber plays a key role to obtain highefficiency. The technologies of controlling thermal radiation spectrum at temperature over 1000oC, however, have not been established yet. We focus on metal-dielectric multi-layer coating. This selective coating shows enormously high absorptance at short wavelength range and sharp cutoff property. Thermal stability test confirms that this multi-layer structure can be one of the candidates for the selective coatings for solar-TPV systems.

Here, closed-end microcavity is proposed in which a semi-transparent metal film was formed atop microcavity. The structure shows weak angular dependence as well as quasi-monochromatic absorptance. Au is employed as material of the cavity walls and the covering thin film. Quasi-monochromatic absorption from the structure is observed in numerical simulation. High quality factor (Q factor) is obtained by strong confinement in the closed-end microcavity. Asymmetric and quasi-monochromatic absorption band with a Q factor of similar to 28 at 1.85 m was observed. This value was about 4-fold larger than that of the open-end microcavity. Additionally, the closed-end microcavity structure filled with SiO2 in cavity exhibits isotropic and quasi-monochromatic thermal radiation over a wide solid angle. This result suggests that both quasi-monochromatic and low-directivity absorptance can be realized by using this configuration.

Feasible study of whole micro-SOFC system using methanol fuel for small power sources in mobile electronic devices was performed. These new power sources are required to achieve heat-self-sustainability and thermal consistency due to its high operating temperature. To satisfy the requirements, energy flow in the system consists of insulation packages stored micro-SOFC was calculated based on thermodynamics, and achievement was evaluated by changing the thickness of insulator. Calculation results confirmed that the requirements were satisfied with small size packages, could be stored in mobile electronic devices. In addition, volumetric energy density of the system was higher than that of Li-ion batteries. Therefore, it was confirmed that the application of micro-SOFC as a new power sources for mobile electronic devices had advantage compared to Li-ion batteries.

High spectral selectivity of thermal radiation is important for achieving high-efficiency energy systems. In this study, intense, narrowband, and low directional absorption/radiation were observed in closed-end microcavity which is a conventional open-end microcavity covered by a semi-transparent thin metal film. The quality factor (Q factor) of optical absorption band strongly depended on the film electrical conductivity. Asymmetric and narrow absorption band with a Q factor of 25 at 1.28 mu m was obtained for a 6-nm-thick Au film. Numerical simulations suggest that the formation of a fixed-end mode at the cavity aperture contributes to the narrowband optical absorption. The closed-end microcavity filled with SiO2 exhibits intense and isotropic thermal radiation over a wide solid angle according to numerical simulation. The narrow and asymmetric absorption spectrum was experimentally confirmed in a model of closed-end microcavity. (C) 2015 AIP Publishing LLC.

The role of thermal management has been critical in the design of electronic devices. This issue is especially important in handheld electronic devices. Here, we investigate a new thermal management technique that controls thermal radiation spectrum using a 2-D periodic microstructure. In this technique, heat generated from an electronic device in the form of thermal radiation directly enters the ambient environment without absorption by external packages such as resin. In this paper, radiative heat transfer in the encapsulated-electronic-device model is experimentally evaluated to clearly show the effect of the proposed technique. This effectiveness of the technique for reducing the temperature of electronic devices and external packages is demonstrated. Moreover, the cooling effect of the technique is clearly observed as the contribution of the radiative heat transfer is increased. This paper suggests that thermal radiation is effective for thermal management of electronic devices in small spaces.

Crystallization process in non-heating pulsed laser deposition (PLO) and the following post-annealing route for perovskite oxide thin film fabrication has been studied. Remarkable influence of sputtering rate on crystallization temperatures is demonstrated for BaZrO3 and SrZrO3 thin films in this process. Crystalline nuclei formation occurs randomly in the thin films deposited at a high sputtering rate which leads to the faster crystallization at a lower temperature, while it occurs predominantly at the substrate or interlayer interface at a higher temperature when the sputtering rate is very low, which is also reinforced by the atomic oxygen irradiation upon deposition. It should be noted that crystalline thin film synthesis of BaZrO3 is possible at a post-annealing temperature below 200 degrees C when the sputtering rate is relatively high. On the other hand, obtained thin films show high tensile strain which is not related to the difference in thermal expansion coefficient between substrate and thin film, but is found to be due to the densification upon crystallization. The tensile strain is relaxed when the thin films are annealed at 750 degrees C or above, while the strain is very stable at a temperature as low as 600 degrees C for 1 week. (C) 2015 Elsevier B.V. All rights reserved.

An anode-supported-type solid oxide fuel cell with a proton-conducting electrolyte composed of LaScO3 co-doped with 32.5 mol% Sr and 2 mol% Co was fabricated using a modified pulsed laser deposition (PLD) method. The modified PLD method, which comprised a conventional PLD method combined with an ultrasonically cleaning procedure, enabled deposition at a temperature lower than the cell fabrication temperatures. Thus, this procedure resulted in the deposition of a dense, gas-tight electrolyte of a poorly sinterable material without interaction between the electrode and electrolyte. The fabricated cell functioned in an intermediate temperature range; open circuit voltages and maximum power densities of the cell were 0.89 V and 8.8 mWcm(-2) at 700 degrees C and 0.91 V and 1.9 mWcm(-2) at 600 degrees C. (C)2015 Elsevier B.V. All rights reserved.

Controlling the thermal radiation spectra of materials is one of the promising ways to advance energy system efficiency. It is well known that the thermal radiation spectrum can be controlled through the introduction of periodic surface microstructures. Herein, a method for the large-area fabrication of periodic microstructures based on multi-step wet etching is described. The method consists of three main steps, i.e., resist mask fabrication via photolithography, electrochemical wet etching, and side wall protection. Using this method, high-aspect micro-holes (0.82 aspect ratio) arrayed with hexagonal symmetry were fabricated on a stainless steel substrate. The conventional wet etching process method typically provides an aspect ratio of 0.3. The optical absorption peak attributed to the fabricated micro-hole array appeared at 0.8 mu m, and the peak absorbance exceeded 0.8 for the micro-holes with a 0.82 aspect ratio. While argon plasma etching in a vacuum chamber was used in the present study for the formation of the protective layer, atmospheric plasma etching should be possible and will expand the applicability of this new method for the large-area fabrication of high-aspect materials.

The influence of gas leakage through penetrated holes introduced during fabrication was experimentally evaluated using in-situ Raman scattering spectroscopy. Gas chromatography analysis of pressure differences between the anode and the cathode revealed that the gas leakage through the holes was dominated by gas diffusion through the anode, and that the pressure difference did not influence the amount of gas leakage. In-situ measurements in an operated cell with a hole revealed combustion between leaked H2 and air occurred around the hole, the O&lt inf&gt 2&lt /inf&gt partial pressure at this hole was not sufficiently low to reduce NiO, and the temperature increased by almost 10°C around the hole. In contrast, no influence on stress distributions was observed.

The electrochemically active area in an SOFC cathode was quantitatively evaluated from &lt sup&gt 18&lt /sup&gt O/&lt sup&gt 16&lt /sup&gt O isotope exchange with/without polarization and following isotopic distribution analysis by second ion mass spectroscopy. For this purpose, we proposed a patterned dense thin film electrode modelling a columnar SOFC cathode, and was fabricated it with La&lt inf&gt 0.6&lt /inf&gt Sr&lt inf&gt 0.4&lt /inf&gt CoO&lt inf&gt 3-δ&lt /inf&gt on a Ce&lt inf&gt 0.9&lt /inf&gt Gd&lt inf&gt 0.1&lt /inf&gt O&lt inf&gt 1.95-δ&lt /inf&gt electrolyte. Compared with the results under open circuit condition, the increase in the isotopic ratio of &lt sup&gt 18&lt /sup&gt O was observed near the electrode/electrolyte interface when a cathodic bias was applied. Such an increase in the &lt sup&gt 18&lt /sup&gt O isotopic ratio was considered due to the electrochemical oxygen incorporation. The electrochemically active area was evaluated as approximately 25 μm in the La&lt inf&gt 0.6&lt /inf&gt Sr&lt inf&gt 0.4&lt /inf&gt CoO&lt inf&gt 3-δ&lt /inf&gt patterned thin film electrode under cathodic polarization of 220 mV in P(O&lt inf&gt 2&lt /inf&gt ) = 1 bar at 973 K.

We demonstrate a high-efficiency solar-thermophotovoltaic system (STPV) using a monolithic, planar, and spectrally selective absorber/emitter. A complete STPV system using gallium antimonide (GaSb) cells was designed and fabricated to conduct power generation tests. To produce a high-efficiency STPV, it is important to match the thermal radiation spectrum with the sensitive region of the GaSb cells. Therefore, to reach high temperatures with low incident power, a planar absorber/emitter is incorporated for controlling the thermal radiation spectrum. This multilayer coating consists of thin-film tungsten sandwiched by yttria-stabilized zirconia. The system efficiency is estimated to be 16% when accounting for the optical properties of the fabricated absorber/emitter. Power generation tests using a high-concentration solar simulator show that the absorber/emitter temperature peaks at 1640 K with an incident power density of 45 W/cm(2), which can be easily obtained by low-cost optics such as Fresnel lenses. The conversion efficiency became 23%, exceeding the Shockley-Queisser limit for GaSb, with a bandgap of 0.67 eV. Furthermore, a total system efficiency of 8% was obtained with the view factor between the emitter and the cell assumed to be 1. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Residual stress in NiO-YSZ was numerically simulated using 2D models consisting of the arrays of NiO and YSZ particles to evaluate the influence of thermal stress due to the large difference of thermal expansion coefficient between NiO and YSZ. The influence of geometric microstructure changed by fabrication processes was also evaluated using the models with different arrangements. Numerical simulation revealed that thermal strains introduced from the hetero-interfaces canceled each other, and residual stress in a uniform model was small. But, in non-uniform model, residual stress increased because counterpart stress was absent at homo-interfaces due to non-uniformity. Simulation results also indicated that a part of particles near the interfaces was exposed to high residual stress as a reaction to thermal stress.

For the quantitative analysis of the effective reaction area in an SOFC cathode, a new type of model patterned electrode was proposed and fabricated with La0.6Sr0.4CoO3-d (LSC). In situ micro X-ray absorption spectroscopy (XAS) measurements were performed in 1 bar of p(O2) at 973 K under open circuit and cathodic polarization. Absorption spectra were taken at different positions with the position resolution of less than 1 μm. The increase in the absorbance, i.e. the decrease in the oxygen potential, was observed near the interface when the electrode was cathodically polarized. The characteristic length of the effective reaction area for the patterned LSC electrode was estimated approximately 20 μm from the interface. Electrochemical impedance spectroscopy measurements were also carried out with the patterned LSC electrode. The characteristic length of the effective reaction area estimated by EIS was close to one by XAS.

A package consisting of a vacuum insulator and a heat exchanger was designed to enable power sources based on micro-SOFCs fueled by liquid fuels thermally sustainable and consistent with other electronics in mobile electronic devices. Gas-liquid heat exchanger worked for cooling the edge of the thermal insulator and recovering the latent and sensible heat of exhaust gases. Numerical analysis using a finite element method and experiment using a prototype package revealed that using liquid fuels based on methanol could reduce the surface temperature of the package to lower than 85°C at the operation temperature lower than 500°C, and thermally sustainable operation could be achieved by heat recovery at this range.

The role of atomic oxygen irradiation in the epitaxial crystallization of yttrium-doped barium zirconate thin films fabricated by pulsed laser deposition (PLO) was investigated. X-ray diffraction and transmission electron microscopy revealed that, for films deposited without irradiation, random nucleation and growth occurred below the onset temperature for continuous crystallization at the film-interlayer interface. In contrast, for films deposited with oxygen irradiation, random nucleation and growth was not detected at the temperature of continuous crystallization, which facilitates epitaxial crystallization in these films. This study suggests the combined low temperature deposition with atomic oxygen irradiation and post-annealing could control microstructure of solid-state electrochemical devices such as solid oxide fuel cells and solid-state lithium secondary batteries. (C) 2014 The Japan Society of Applied Physics

Sr2+, Al3+-doped LespO(3) perovskite-type oxide (La0.675Sr0.325Sc0.99Al0.01O3; LSSA), which exhibits high conductivity of both oxide-ion and proton, is expected to become an electrolyte material for high-temperature solid oxide fuel cells (SOFCs). Considering the potential of this material to serve as a solid electrolyte, its chemical compatibility with some of the typical fuel electrodes commonly used in SOFCs was investigated. Severe elemental diffusion was found at the sintering temperature of 1673 K between doped LaScO3 and the anode material, mainly due to strontium migration. To control the elemental diffusion, we lowered the sintering temperature to 1523 K. In the case of Ni-SDC, we found no elemental diffusion at the electrolyte/electrode interface. Moreover, we tried to fabricate SOFC consisting of LSSA electrolyte and some electrodes, and we performed power generation tests above 1073 K. At 1273 K, the maximum power density was 158 mW cm(-2) as humidified hydrogen fuel. The electrolyte resistance was high due to the high thickness of 0.6-0.9 mm. Higher power density would seem possible if a thinner electrolyte is applied. Consequently, we found that LSSA is applicable as an electrolyte material for SOFCs. (C) The Electrochemical Society of Japan, All rights reserved.

Making surface microstructures on refractory metal is one of the promising technologies of controlling optical property at high-temperature condition. However, the technique of fabricating microstructures for refractory metal is limited, such as using semiconductor technologies. Therefore, the large-area fabrication of periodic microstructures on refractory metals is a key technology supporting the practical application of controlling optical property using surface microstructures. This report describes large-area fabrication of two-dimensional submicron quasi-periodic microcavities using self-organization on a nickel-based superalloy. The surface microcavities on a bulk metal were obtained by appropriate heat treatments and simple chemical etching process. The spectrally selective property attributed to the confined modes inside cavities is observed. The selective absorbing property and thermal stability are also confirmed at 973 K. Therefore, this fabrication method can be applied for high temperature solar selective absorbers. The fabricated sample showed solar absorptance of 0.74 and emittance of 0.25 at 873 K. The performance of solar selective absorber is verified by simple heating test using the sample with randomly arrayed microstructures. It is indicated that the temperature of microstructured sample shows 30 degrees C higher than that of a black-painted sample. (C) 2014 The Authors. Published by Elsevier Ltd.

In solar thermophotovoltaic (STPV) generation systems, the thermal radiation from emitters heated by the high temperature solar absorbers is converted into electricity at a photovoltaic (PV) cell. STPV systems have some advantages over PV generation systems. For instance, it is possible to control the thermal radiation spectrum of the emitter. Generally, the PV cell has an inherent sensitive region where an incident photon excites the electron. Enhancing the thermal radiation in this sensitive region of the PV cell, therefore, increases the generation efficiency. Theoretically, the efficiency of STPV systems can reach up to 85% when Carnot efficiency is considered and up to 45% when a monochromatic radiation releasing emitter is used. However, the experimental STPV system is less efficient than theoretical one as a consequence of the large amount of heat loss from the high-temperature absorber/emitter system. The purpose of this study is to achieve a high-efficiency STPV generation system using a monolithic planar spectrally selective absorber/emitter. The temperature superiority of the monolithic planar absorber/emitter is estimated by using spectral and thermal properties of STPV system components. Using the enitre configuration of the STPV system, a system efficiency of over 10% is estimated in this study.

Thermophotovoltaic (TPV) system is expected to generate electrical power from various heat sources. One of the key devices of TPV system is spectrally control thermal emitters. The performance is not sufficient to achieve high efficient TPV systems. In this study, we developed new t,,pe spectral selective emitters with closed-end surface microcavit,, array. The simulated spectral thermal radiation band width is only 70nm and Q-value=26.4. This Q-value is 5 times larger than the conventional open-end microcavity emitters. The design of Solar-TPV system which is driven by concentrated solar energy using refractory metal emitters with multilayer coating. The estimated system efficiency and electric power density using the experimentally obtained spectral property of the selective emitters is 16.6% and 2.9W/cm(2), respectively. (C) 2014 Published by Elsevier Ltd.

In these days, the application of using thermal energy of sunlight has become widely used in concentrated solar power generation systems (CSP). In CSP, property of the receiver directly contributes to the system efficiency of CSP. The solar selective absorber is used for the receiver to reduce energy loss of thermal radiation. To investigate the mass production technology of fabricating solar selective absorber that can be utilized in high temperature condition, we focused on transparent conductive oxides (TCO) thin film on metal substrate. TCO material has plasma wavelength in infrared region. Therefore the electromagnetic wave with shorter wavelength than plasma wavelength goes through the material, while the electromagnetic wave with longer wavelength is reflected on the surface. It is realized that TCO on metal substrate showed high performance as solar selective absorbers, i.e. high absorptance in visible light range and low emittance in infrared range by numerical simulations. The optical property of fabricated TCO coated metal is well consistent with the simulated property. Consequently, we attain high performance solar selective absorber of which solar absorptance is 0.71 and hemispherical total emittance is 0.11. The thermal stability is also confirmed at 600 degrees C in vacuum for 3 hr. (C) 2014 The Authors. Published by Elsevier Ltd.

Proton transport properties of a partially protonated poly(aspartic acid)/sodium polyaspartate (P-Asp) were investigated. A remarkable enhancement of proton conductivity has been achieved in the thin film. Proton conductivity of 60-nm-thick thin film prepared on MgO(100) substrate was 3.4 X 10(-3) S cm(-1) at 298 K. The electrical conductivity of the oriented thin film was 1 order of magnitude higher than the bulk specimen, and the activation energies for the proton conductivity were 0.34 eV for the oriented thin film and 0.65 eV for the pelletized sample, respectively. This enhancement of the proton transport is attributable to the highly oriented structure on MgO(100) substrate. This result proposes great potential for a new strategy to produce a highly proton-conductive material using the concept of an oriented thin film structure without strong acid groups.

Barium zirconate based proton conducting thin films were fabricated using PLD method with ArF Excimer laser under high and low oxygen partial pressures on silicon wafers, and stress conditions and its transition by thermal annealing were measured by XRD side inclination method. Stress conditions were changed by thermal annealing, and two stress transition modes were observed. Stress condition in the films deposited at high oxygen partial pressure was compressive and the value was changed to tensile by thermal annealing. Considering the difference of thermal expansion coefficient, stress condition due to thermal stress was tensile. Therefore, this transition was defined as stress relaxation. By contrast, the films deposited at low oxygen partial pressure showed tensile stress condition, and transited to compressive stress condition, i.e. stress increment. These two modes were probably due to the transition of intrinsic stress caused by surface energy, which was sensitive to the deposition atmospheres.

Stress in yttria stabilized zirconia (YSZ) thin films was controlled by using various substrates, which had different thermal expansion coefficient (TEC), and electrical properties of the films were measured to study the relationship between the stress filed and electrical properties. Thin films of YSZ were deposited by PLD method on Al2O3 and AlN substrates. Because TEC of YSZ is larger than that of the substrates, tensile stress field was introduced into the films at room temperature. Measured stress value by XRD was varied from 0.7 to 1.7 GPa at R. T. This value is significantly higher than literature value. However, the films also showed different lattice volume on the different substrates. Although electrical properties in the films showed different tendencies by the substrates, both stress field and lattice volume were different. Hence, stress dependence of electrical properties was not clearly observed.

Stress in an anode-supported type solid oxide fuel cell (SOFC) was measured by in-situ measurement using micro Raman scattering spectroscopy. The stress conditions evaluation method focuses on Raman spectra of samarium-doped ceria (SDC) which was used as an interlayer in SOFC. The shift of ceria Raman peak and peak width in SDC interlayer were measured to evaluate stress, temperature, and Sm concentration. We performed this method in the purchased cells of conventional anode-supported type SOFC under thermal cycles, which simulate start-up and shout down. Observed results suggested that not only thermal stress relaxation but also diffusion of samarium from an interlayer to an electrolyte, and stress relaxation by plastically deformation were occurred.

The high-temperature photonic materials fabricated by practicable technology is described. The high-temperature photonic material using self-organization of a super-alloys and a monolithic planer absorber/emitter with multi-layer coating is obtained. Renewable Energy and the Environment Congress © 2013.

A planar absorber/emitter in solar thermophotovoltaic system reaches high temperature with a small concentration ratio because of low thermal radiation loss. Using this planar absorber/emitter, the net efficiency is estimated to be 21%. Renewable Energy and the Environment Congress © 2013.

A package for the power source of mobile electronic devices based on micro solid oxide fuel cells (micro-SOFCs) was designed considering thermal management. The package should suppress its surface temperature lower than harmless value for other electrical circuits, and thermal consistency should be kept. In addition, other functions such as gas flow and electrical connection were installed into the package. Hence, high performance thermal insulation structure with good machinability was necessary. We applied thermal insulation structure made of Si wafers and glasses by MEMS technologies. The convection heat transfer was prevented by the structure equipped with a vacuum zone. Experimental and theoretical consideration revealed that the purpose could be achieved at apparent thermal conductivity of the structure lower than 0.02 W/ mK. In accordance with the consideration, a package was designed, and its thermal insulation performances were evaluated.

Large-area fabrication of periodic microstructures on refractory metals surface is a key technology supporting the practical application of spectrally controlled thermal radiation using surface microcavities. This report describes large-area fabrication of two-dimensional submicron quasi-periodic microcavities using self-organization on a nickel-based superalloy. The surface microcavities on a bulk metal are obtained by heat treatment and simple chemical etching. The emission peak attributed to the confined modes inside cavities can be tuned by controlling the microcavity size from 0.27 to 0.53 mu m. Emittance enhancement and thermal stability are also confirmed at 973 K. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4767903]

We studied the relation between the Raman peak shift of the ceria F-2g peak and isostatic pressure in rare-earth-doped ceria, which is used as interlayer in anode-supported SOFCs. to evaluate the stress in operational anode-supported SOFCs. First, 10 and 20 mol% Sm- and Gd-doped ceria, and pure ceria were isostatically compressed up to 10 GPa in a diamond anvil cell and the Raman spectra were measured at each pressure. Based on the results and reported elastic properties, the relation was retrieved for rare-earth-doped ceria under anisotropic stress. Although rare-earth-doped ceria showed different behavior than pure ceria, the difference due to the dopant and its concentration was small. The obtained ratio between anisotropic pressure and Raman peak shift in rare-earth-doped ceria was 0.441 GPa/cm(-1), and this value indicates that a change of 1 GPa in anisotropic stress will shift the Raman peak by approximately 2.3 cm(-1). Hence, a Raman system, which can measure the Raman peak shift with an accuracy of 0.1 cm(-1), can recognize differences in stress conditions in the interlayer to an accuracy of approximately 40-50 MPa. (C) 2012 Elsevier By. All rights reserved.

Mechanical properties of Ni-YSZ cermet (Ni 30, 44, 58 vol.%) in SOFC operating conditions in the temperature range of room temperature to 1000°C and in reduction atmospheres, were studied by an in situ four points bending method. Ni30 specimens in the whole testing temperature and Ni44, Ni58 specimens at the temperature lower than 350 °C fractured brittly, and Ni44, Ni58 specimens fractured with plastic deformation at the temperature higher than 350 °C. In the microstructure of three Ni contents, nickel was aggregated and isolated in Ni30 specimens. By contrast, nickel was well distributed in Ni44, 58 specimens. In addition, the yield strength of nickel decreases at the temperatures higher than 300 °C. Hence, observed results suggested being due to the local yield of well distributed nickel in the cermet. Because anode supported type SOFCs employ Ni-YSZ cermet, which nickel content is higher than 44 vol.%, this study suggests that an irreversible deformation occur during SOFC operation due to the plastic deformation of Ni-YSZ cermet.

Creep properties of strontium doped lanthanum manganite (LSM) were studied in SOFC operating conditions, i.e. in the temperature range of 800°C to 1050°C and in air and argon gas environment. Although the difference of atmosphere did not affect creep properties, temperature and applied stress dependence of steady-state creep rate changed around 900°C. Considering previous reports, it was concluded that dominant creep mechanism of LSM in the temperature range of 950°C to 1300 °C was diffusion creep and the dominant creep mechanism changed at the temperature lower than 900°C. This indicated that dominant creep mechanism was grain boundary sliding creep. Because grain boundary sliding creep showed higher stress dependence and lower temperature dependence than diffusion creep, creep deformation during SOFC operation will be larger than expectations based on diffusion creep.

Ni-YSZ composites are widely used as SOFC anode materials for electrochemical devices. The mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method under SOFC operating condition. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol.%, 15:85 vol.%, 30:70 vol.%, and 50:50 vol.%. Electrical resistivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol.%. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of NiO-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment.

Ni-YSZ composites are widely used as SOFC anode materials for electrochemical devices. The mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method under SOFC operating condition. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol.%, 15:85 vol.%, 30:70 vol.%, and 50:50 vol.%. Electrical resistivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol.%. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of NiO-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment. © 2012 The Japan Society of Mechanical Engineers.

Creep properties of strontium doped lanthanum manganite (LSM) were studied in SOFC operating conditions, i.e. in the temperature range of 800 °C to 1050 °C and in air and argon gas environment. Although the difference of atmosphere did not affect creep properties, temperature and applied stress dependence of steady-state creep rate changed around 900 °C. Considering previous reports, it was concluded that dominant creep mechanism of LSM in the temperature range of 950 °C to 1300 °C was diffusion creep and the dominant creep mechanism changed at the temperature lower than 9OO°C. This indicated that dominant creep mechanism was grain boundary sliding creep. Because grain boundary sliding creep showed higher stress dependence and lower temperature dependence than diffusion creep, creep deformation during SOFC operation will be larger than expectations based on diffusion creep. © 2012 The Japan Society of Mechanical Engineers.

Mechanical properties of Ni-YSZ cermet (Ni 30, 44, 58 vol.%) in SOFC operating conditions in the temperature range of room temperature to 1000 °C and in reduction atmospheres, were studied by an in situ four points bending method. Ni30 specimens in the whole testing temperature and Ni44, Ni58 specimens at the temperature lower than 350 °C fractured brittly, and Ni44, Ni58 specimens fractured with plastic deformation at the temperature higher than 350 °C. In the microstructure of three Ni contents, nickel was aggregated and isolated in Ni30 specimens. By contrast, nickel was well distributed in Ni44, 58 specimens. In addition, the yield strength of nickel decreases at the temperatures higher than 300 °C. Hence, observed results suggested being due to the local yield of well distributed nickel in the cermet. Because anode supported type SOFCs employ Ni-YSZ cermet, which nickel content is higher than 44 vol.%, this study suggests that an irreversible deformation occur during SOFC operation due to the plastic deformation of Ni-YSZ cermet. © 2012 The Japan Society of Mechanical Engineers.

The electronic structures in the surface and bulk states of Y³⁺-doped BaZrO₃ (BaZr_1-<i>x</i>Y_<i>x</i>O_3-δ) have been studied by X-ray absorption spectroscopy and soft-X-ray emission spectroscopy. The valence band is mainly composed of the O 2<i>p</i> state hybridized with the Zr 4<i>d</i> state. The conduction band consists of Zr 4<i>d</i> state. The band gap increases with increasing Y³⁺ concentration, indicating the existence of hole at the top of valence band. Although the Fermi level (<i>E</i>_F) of bulk locates at the valence band side, <i>E</i>_F of surface locates at intermediate of band gap. These findings may indicate that the band bending effect exists at the surface of BaZr_1-<i>x</i>Y_<i>x</i>O_3-δ.

Hydrogen energy infrastructure is expected to be a key technology for developing a sustainable society. However, the production route of hydrogen is still an important open problem. One prospective route of hydrogen production is a solar hydrogen system. In such a system, the thermal radiation spectrum, which plays an important role in chemical reactions, can be controlled by applying a two-dimensional surface grating to radiative materials. We used spectrally controlled thermal radiation to promote methane-steam reforming. Therefore, we demonstrated that hydrogen production strongly depends on the spectral intensity within the particularly resonant wavelength range, and that the amount of hydrogen produced is 5.8 times greater than that using normal thermal radiation. The conceptual design of a solar hydrogen system using spectrally controlled radiation is presented.

The spectral properties of thermal radiation can be controlled by surface microstructures with feature size in the optical wavelength range. We applied this technology to solar selective absorbers for concentrated solar power (CSP) generation systems. We investigated the spectral properties and thermal stability of two-dimensional periodic microstructures on a tungsten (W) surface to develop solar selective absorbers for high-temperature applications. The developed absorbers exhibited good spectral selectivity and sufficient thermal stability under vacuum. Although we could verified that the microstructured solar selective absorbers improved CSP efficiency, this method cannot be put into practical use because of cost and time, and also because there is currently no technology for fabricating surface gratings on high melting point materials over a large area. Therefore, we used W-Cu alloys to investigate an approach to mass production of surface microcavity structures over a large area. We then confirmed that the absorptivity in the visible light range could be increased by using this simple method.

At present, the utilization of thermal energy from sunlight has been widely adopted as the working principle of concentrated solar power (CSP) generation systems. In this research, we suggest a CSP technology based on the properties of transparent conductive oxide (TCO) thin films on metal substrates which is compatible with mass production of solar selective absorbers that can be utilized at high temperatures. Since the plasma wavelength of TCO materials is in the infrared region, electromagnetic waves with wavelengths longer than the plasma wavelength are reflected at the surface, whereas electromagnetic waves with shorter wavelengths pass through the surface layer and reach the substrate. In other words, a TCO thin film behaves as an antireflection film only in the transparency range of TCO coating. This phenomenon is demonstrated through numerical simulations based on rigorous coupled-wave analysis (RCWA). The prepared samples also show favorable spectral selectivity and satisfactory performance as solar selective absorbers, with a solar absorntance of 0.76, a thermal emittance of 0.12 at 800 degrees C and a spectral selectivity of 6.5 at 800 degrees C.

For the commercialization of solid oxide fuel cell (SOFC), in addition to the electrochemical reliability, it is also important to ensure the mechanical reliability of SOFC. Thus, the establishment of a suitable mechanical testing method under various temperatures and oxygen partial pressure conditions is a prerequisite for the development of reliable SOFCs. In this study, the in-situ mechanical testing method was developed in order to investigate mechanical property (i.e.: Elastic modulus and Fracture strength, Creep and Fatigue property) of solid oxide fuel cells components under high oxidizing/reducing environments. And mechanical property of gadolinium doped ceria (Gd0.1Ce0.9O2-δ ; GDC) as oxygen non-stoichiometric compounds were evaluated in oxygen partial pressures under reducing conditions by developed In-situ mechanical testing machine. The experimental results of the investigation of elastic modulus and fracture strength on the SOFC components, the fracture stress of GDC were almost constant regardless of oxygen partial pressure, while elastic modulus decreased with decreasing oxygen partial pressure in reducing atmospheres. Mechanical properties of SOFC materials should be characterized by in-situ method because these results are different to quench method.

Photocurable electrolytes were prepared by mixing proton-conductive polymer sulfonated poly(ether ether ketone) (SPEEK), cross-linking monomer divinyl sulfone (DVS), photoinitiator phenylbis(2,4,6-trimethylbenzoyl) phosphineoxide (PI), dimethylacetamide (DMA), and ethanol. To investigate the proton transport property, a series of photocurable electrolytes with various PI content ratios were prepared to form photocured membranes. Water uptake, ion exchange capacity (IEC), proton conductivity, and water-resistance of the photocured membranes were investigated. Water-resistant photocured membrane is easy to prepare, which gives relatively high proton conductivity (28 mS cm(-1) under 70 degrees C and relative humidity of 90%). Patterning of micro-structure on the photocured membrane was also demonstrated by using the property of the photocurable electrolytes. (C) 2011 Elsevier B.V. All rights reserved.

Iridium oxide supported on Vulcan XC-72 carbon black (IrO(2)/C) as a cathode catalyst for polymer electrolyte fuel cell (PEFC) has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurement. The IrO(2) particles were 8-160 rim in diameter. The oxygen electroreduction activity was studied by cyclic voltammetry (CV). It was found that IrO(2)/C had high oxygen reduction reaction (ORR) activity. The performance of the membrane electrode assemble (MEA) was also tested in a single PEFC and showed that IrO(2)/C catalyst would be potential candidates for use as cathode catalyst in PEFC. (C) 2011 Elsevier B.V. All rights reserved.

Proton concentration as a function of ambient temperature in 15 mol% Y-doped BaZrO3 proton conductors prepared at 1800 degrees C, 1600 degrees C and 1400 degrees C, is measured by thermo-gravimetric (TG) analysis. TG analysis reveals that the maximum proton concentration in the specimen prepared at 1400 degrees C is over 15 mol%. The value is over the limitation decided by hydration process via oxygen vacancy. Infrared diffuse reflection spectroscopy confirms that additional O-D stretching vibration exists in the specimen. Both results strongly suggest that not a few amounts of water incorporate in the specimen prepared at low temperature through other hydration process. (C) 2010 Elsevier B.V. All rights reserved.

For the commercialization of solid oxide fuel cell (SOFC), in addition to the electrochemical reliability, it is also important to ensure the mechanical reliability of SOFC. Thus, the establishment of a suitable mechanical testing method under various temperatures and oxygen partial pressure conditions is a prerequisite for the development of reliable SOFCs. In this study, the in-situ mechanical testing method was developed in order to investigate mechanical property (i.e.: Elastic modulus and Fracture strength, Creep and Fatigue property) of solid oxide fuel cells components under high oxidizing/reducing environments. And mechanical property of gadolinium doped ceria (Gd 0.1Ce 0.9O 2-δ GDC) as oxygen non-stoichiometric compounds were evaluated in oxygen partial pressures under reducing conditions by developed In-situ mechanical testing machine. The experimental results of the investigation of elastic modulus and fracture strength on the SOFC components, the fracture stress of GDC were almost constant regardless of oxygen partial pressure, while elastic modulus decreased with decreasing oxygen partial pressure in reducing atmospheres. Mechanical properties of SOFC materials should be characterized by in-situ method because these results are different to quench method. © 2011 The Japan Society of Mechanical Engineers.

Recently, the spectral properties of thermal radiation have been controlled by surface gratings having a size in the optical wavelength range, and this technique has been applied to improve the efficiency of energy systems, e.g., thermophotovoltaic generators and sky radiators. In this paper, the technique was applied to an advanced cooling system for electronic devices. In general, electronic devices are packaged in resin to protect them from damage; however, resin prevents heat from escaping from the package because of resin's strong absorption of thermal radiation in the infrared range and low thermal conductivity. By controlling the spectral property of thermal radiation from electronic devices, the thermal radiation absorbed by resin can be decreased. As a result, a cooling system for electronic devices is possible. At first, we performed a numerical simulation to design the optimal surface gratings to cool electronic devices packaged in epoxy resin. The surface gratings were fabricated using a MEMS process. The performance of the fabricated emitter was evaluated experimentally. In conclusion, we confirmed that this new cooling technique will be effective for electronic devices.

Y-doped BaZrO3 (BZY) is an outstanding proton conductor under wet atmosphere at relatively low temperatures (&lt;600 degrees C). Dense polycrystalline ceramics of this material used in intermediate-temperature solid oxide fuel cells as solid electrolytes, however, suffer from uniquely high resistance across grain boundaries in the materials. It has long been speculated that such high resistance at the grain boundaries is originated from potential barriers which may be formed at the grain boundaries. Here we provide direct experimental evidence that Schottky-type potential barriers indeed exist at grain boundaries in BZY. The results of our study on dc-bias dependence of grain-boundary impedance in 5, 3 and 2 mol% Y-doped BaZrO3 (BZY5, BZY3, and BZY2, respectively) clearly show that the relation between the current across a grain boundary and the applied dc-bias is ohmic where the dc-bias is lower than the thermal voltage, while that becomes superohmic at sufficiently high biases. In addition, it is found that the capacitance of the grain boundary decreases with the bias. These observations are consistent with what is expected from the thermionic emission mechanism for a current across a potential barrier. Hence we unambiguously verified that Schottky-type potential barriers are formed at grain boundaries in BZY to serve as extra internal resistors, and are responsible for high grain-boundary resistance observed in polycrystalline BZY ceramics. The barrier heights estimated for BZY5, BZY3, and BZY2 are 0.51, 0.85, and 0.95 V, respectively.

We fabricated micro solid oxide fuel cells with perovskite type proton conductors on silicon substrates, and evaluated their electrical properties using electrochemical impedance spectroscopy (EIS). The cells with 15 mol% yttrium-doped BaZrO3 and Pt-Pd electrodes could resist several thermal cycles from room temperature to 317 degrees C, and they showed sufficient open circuit voltage over 1 V around 300 degrees C, if physical gas leakage was properly prevented. Maximum power density of cells reached 8.4 mW/cm(2) at 270 degrees C. This value was quite promising for low temperature operation. But, the results of power generation test were so different from each other and difference was sometimes over two orders of magnitude. EIS results indicated the contribution of electrolyte resistance to total resistance was small and those differences were due to the difference of electrode reaction components.

Numerical simulations are performed to characterize the micro- and macro-scale aspects of the electro-chemo-mechanical coupling behavior of a positive-electrolyte-negative (PEN) structure under SOFC operation. The mathematical homogenization method is applied to evaluate the macroscopic material properties of porous electrodes by performing the corresponding microscopic analyses. In particular, the potential transfer conditions at pore surfaces and triple-phase boundaries are homogenized to be source terms in the macroscopic electron-ion coupled transport problem. A case study is conducted to identify the major source of generation and evolution of cracks running through a disc-shaped cell. In this context, we are concerned especially with the effects of the radius of the cell, the thickness of the electrolyte and the profile of temperature's in-plane distribution on the macroscopic tensile circumferential stress distributions.

Micro-solid oxide fuel cells (Micro-SOFCs) with yttrium-doped barium zirconate (BZY) and strontium and cobalt-doped lanthanum scandate (LSScCo) electrolytes were fabricated for low-temperature operation at 300 °C The micro-SOFC with a BZY electrolyte could operate at 300°C with an open circuit voltage (OCV) of 1.08 V and a maximum power density of 2.8 mW/cm 2. The micro-SOFC with a LSScCo electrolyte could operate at 370°C its OCV was about 0.8 V, and its maximum power density was 0.6 mW/cm . Electrochemical impedance spectroscopy revealed that the electrolyte resistance in both the micro-SOFCs was lower than 0.1 Ωcm 2, and almost all of the resistance was due to anode and cathode reactions. Although the obtained maximum power density was not sufficient for practical applications, improvement of electrodes will make these micro-SOFCs promising candidates for power sources of mobile electronic devices. © 2011 Materials Research Society.

We have developed a method for evaluating stress conditions in operated SOFCs based on in-situ Raman scattering spectroscopy. This method uses F-2g vibration mode of CeO2 in interlayer of anode supported type SOFC as a probe, and we can calculate stress in an interlayer, i.e. stress in an electrolyte from the shift of a Raman peak. We apply this method to typical anode supported type cells and evaluate stress conditions during operation. Using this method, stress conditions in the electrolyte before operation is evaluated to be compressive, consistent with XRD and literature. During operation, stress conditions changed by the reduction of NiO to Ni; the compressive stress changed to tensile. In addition, the standard deviation of stresses became larger than before re-oxidation, and nonreversible. These results indicate that compressive residual stress introduced into the electrolyte during fabrication process is relaxed, and suggest that an electrolyte becomes mechanically unstable during operation.

Effects of redox cycling on the mechanical properties of Ni-YSZ cermets were investigated by using an in-situ small punch (SP) testing method. The Ni contents in the Ni-YSZ cermets tested in this study were 0, 15, 30 and 50 vol.%. Electrical conductivity measurements suggested that Ni particles formed a network-like structure at Ni contents greater than 20 vol.%. Experimental results obtained from the in-situ SP tests at 800 degrees C demonstrated that ductile-like deformation was induced under reducing environment (at an oxygen partial pressure of 10(-18) atm) for the Ni contents of 30 and 50 vol.%. The ductile-like behavior was attributable to the formation of Ni network. The first complete re-oxidation of Ni-YSZ cermets then caused critical damage and resulted in drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ cermets under reducing environments.

We performed structural optimization of a selective emitter with two-dimensional silicon based gratings coated by platinum as a thermal radiator to promote methane steam reforming reaction. The structural parameters were optimized by numerical calculation to radiate high thermal power in a vibrational absorption band of methane molecule at 3.3 mu m. Optical property of the fabricated optimum selective emitter with periodicity Lambda = 2.6 mu m found that the emission peak was resonant with this absorption band. The amount of hydrogen produced by the methane steam reforming process using the optimized selective emitter became four times greater than that obtained by the flat emitter.

By controlling the thermal radiation spectrum using surface grating technologies, we promote the methane steam reforming to produce hydrogen. We fabricated a two-dimensional surface grating to tune its thermal emittance peak to the vibrational absorption bands of methane and water. We demonstrated that hydrogen production strongly depends on the spectral intensity within the resonant wavelength range, and that the hydrogen production rate is four times greater than that obtained when the spectrally controlled thermal radiation is not tuned to vibrational resonances. The optical excitation of the vibrational energy levels of gas molecules is found to effectively promote hydrogen production. (C) 2010 American Institute of Physics. [doi:10.1063/1.3525164]

The influence of chemically induced expansion on the fracture damage of a nonstoichiometric oxide (ceria) based solid oxide fuel cell (SOFC) single cell laminate was investigated by using numerical stress analyses under oxidizing/reducing gradient condition. The single cell examined in this study was composed of electrolyte (Ce(0.8)Sm(0.2)O(2-delta)), anode (Cermets of Ni-Ce(0.8)Sm(0.2)O(2-delta)). and cathode (La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-delta)), respectively. The finite element method (FEM) was employed to calculate the residual stress, thermal stresses, and chemically induced expansion stresses for the single cell. The residual and thermal stresses were calculated touch smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically induced expansion stresses were shown to remarkably increase for the temperature range greater than 973 K and accounted their magnitude for primary part of the induced stress. It was shown from the FEM that the maximum circumferential stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission (AE) method. (C) 2010 Elsevier B.V. All rights reserved.

The iridium oxide nanoparticles supported on Vulcan XC-72 porous carbon were prepared for cathode catalyst in polymer electrolyte fuel cell (PEFC). The catalyst has been characterized by transmission electron microscopy (TEM) and in PEFC tests. The iridium oxide nanoparticles, which were uniformly dispersed on carbon surface, were 2-3 nm in diameter. With respect to the oxygen reduction reaction (ORR) activity was also studied by cyclic voltammetry (CV), revealing an onset potential of about 0.6V vs. an AgiAgCl electrode. The ORR catalytic activity of this catalyst was also tested in a hydrogen-oxygen single PEFC and a power density of 20 mW cm(-2) has been achieved at the current density of 68.5 mA cm(-2). This study concludes that carbon-supported iridium oxide nanoparticles have potential to be used as cathode catalyst in PEFC. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Poly(aspartic acid) and its thin film were synthesized to study proton transport properties. The average degree of polymerization and molecular weight are 50 and 7000, respectively. The proton conductivities of the Poly(aspartic acid) and its thin film were 4.3 × 10- 4 and 5.1 × 10- 3 S cm- 1, respectively under the relative humidity of 70% and 298 K. The proton conductivity of the thin film is one order of magnitude higher than that of the pelletized Poly(aspartic acid). The activation energies for the proton conduction of the pelletized Poly(aspartic acid) and thin film are 0.65 and 0.53 eV, respectively. The open circuit voltage of the pelletized sample exhibited ~ 0.9 V under the relative humidity of 70% and 298 K. © 2009 Elsevier B.V. All rights reserved.

The electronic structure near the top of the valence band and the bottom of the conduction band for Sr-doped LaScO3 single crystal was investigated by X-ray absorption spectroscopy (XAS). The conduction band consists mainly of the Sc 3d state hybridized with the O 2p state. A defect-induced localized level is observed below the Sc 3d state of the Sr-doped single crystal. The XAS spectrum of a wet-annealed crystal shows a broad absorption around the top of the valence band that may be related to the level of holes based on the related charge carrier map of Sr-doped LaScO3. (C) 2010 The Japan Society of Applied Physics

Proton transport properties across the grain boundary of barium zirconate based proton conductors were studied in accordance with the space charge concept. The analysis is performed at temperatures lower than 200 degrees C using a Mott-Schottky model. The barrier height of Y- and Gd-doped barium zirconate is in the range of 0.29 to 0.57 V, which higher than that of oxygen ionic conductors. The barrier height of the space charge layer shows a dependence on the dopant type and concentration. The dependence correlates with the enrichment of the dopant at the grain boundary. The results suggest that the enrichment of the dopant decreases the barrier height and is effective to improve proton transport properties across the grain boundary.

The conductivity and elastic modulus Of (CeO2)(1 - x)(YO1.5)(x) for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y2O3: this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity. the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content Of Y2O3 dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y2O3 dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y2O3, which also agreed with the experimental results. It was shown that the Y-O-Y bonding energy increased with the increasing content of Y2O3 dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y-O-Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y2O3 dopant content of approximately 20 mol%. (C) 2009 Elsevier B.V. All rights reserved.

New proton-conductive polyamide oligomers, oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thin films. The obtained oligomers were characterized by the X-ray diffraction, FT-IR spectra, 1H NMR, Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrum, and electrical conductivity measurements. The bulk proton conductivity is 3.0 × 10- 4 S cm- 1 at the relative humidity (RH) of 80%. The proton conductivity of thin film is relatively higher than that of bulk sample. Thickness dependence of the proton conductivity was observed in these thin films. The maximum proton conductivity of the thin film is 4.0 × 10- 3 S cm- 1 at the relative humidity (RH) of 80%, which is higher one order magnitude than that of the bulk sample. The activation energies of bulk and 200 nm thick film are 1.0 and 0.69 eV at the RH of 60%, respectively. © 2008 Elsevier B.V. All rights reserved.

The relationship between chemical composition at a grain boundary and specific grain boundary conductivity is Studied in Y-doped BaZrO(3) ceramics sintered at 1800 degrees C. Y enrichment at the grain boundary as yttrium concentration increased and Ba deficiency in ceramics as an increase of sintering time are observed. At the grain boundary, phase segregation, i.e. existence of secondary phase and amorphous phase which prevent proton migration, is not observed. The results indicate that at the grain boundary, concentration of Ba vacancy and Y substituted into Zr site is changed. Grain boundary conductivity shows significant dependences to Ba deficiency and Y concentration in ceramics. It is due to significant dependences of specific grain boundary conductivity to Ba deficiency and Y concentration in ceramics. The results indicate that proton migration across the grain boundary is sensitive to concentration of those effectively charged defect, i.e. Y substituted into Zr site and Ba vacancy at grain boundary. (C) 2008 Elsevier B.V. All rights reserved.

Proton transport properties of three thin films (110, 240, and 360 nm thick films) on R-plane (1102) sapphire substrates for oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] were investigated. The maximum proton conductivity of the thin film is 1.7 × 10-3 S cm-1 at the RH of 80%, which is five times higher than that of the bulk sample (3.0 × 10-4 S cm-1). The activation energies of the 110, 240, and 360 nm thick films are found to 0.74, 0.67, and 0.68 eV at the RH of 80%, respectively.© 2009 The Surface Science Society of Japan.

This paper describes the fabrication technology of micro solid oxide fuel cells (SOFC) using Gddoped CeO_2 (GDC) solid oxide electrolyte. A GDC membrane is made extremely thin (〜300nm thick) for low temperature operation, and a microheater is formed on the GDC membrane for local heating. To fabricate the self-supported GDC membrane, the stress of GDC films deposited by pulse laser deposition (PLD) was reduced by controlling partial O_2 pressure during deposition. The etch resistance of the GDC film against several chemicals was investigated to design the fabrication process of the micro SOFC. Using the designed fabrication process, the core structure of the micro SOFC was successfully fabricated. The ionic conductivity of the self-supported GDC membrane is approximately identical to that of bulk GDC. The area specific resistivity of the self-supported GDC membrane is as low as 0.15Ωcm^2 at 500℃.

Oxygen potential distribution in a ZrO2-based solid electrolyte in the vicinity of a dense film platinum electrode under a current flow was investigated by using in-situ micro x-ray absorption spectroscopy. The oxide ion conductor (Y2O3)(0.08)(ZrO2)(0.92) doped with 2.5 mol% of Mn2O3, in which the valence state of manganese ions could be used as an indicator for evaluating the oxygen potential, was chosen as a model electrolyte. As results, a drastic drop of oxygen potential was apparently observed near the triple phase boundary. The proposed method was found to be principally applicable for the direct observation of the oxygen potential distribution in an oxide ion conductor under a current flow.

An electrolyte supported intermediate temperature SOFC (IT-SOFC) using 15 mol% Y-doped BaZrO3 (BZY15) is fabricated and tested in the temperature range from 550 degrees C to 650 degrees C to study fundamental properties of an IT-SOFC using proton conductors. The measurement of I-V characteristics and impedance spectra reveal that BZY15 is superior to oxygen ionic conductors as an electrolyte material from the viewpoint of electrolyte resistance in the tested temperature range. The results also confirm the necessity of reducing cathodic overpotential.

Mechanical damages and their formation mechanisms in SOFC were investigated. Generalized schemes of the occurrence of mechanical failures were summarized, and among them, common features in various cell designs were extracted. They were discussed in three categories of (a) deformation of a cell due to its asymmetry, (b) propagation of mechanical defects, and (c) effects of irregular operations. Prototype-cell experiments were designed to reproduce the key features, and to develop a quantitative evaluation scheme of operational margins for prediction of the short and long term reliability of a specific cell design. Numerical calculation tools based on finite element method and homogenization method are designed. Experimental methods were developed to acquire high-temperature mechanical behaviors of the materials and cell stacks.

The electronic structure of La1-xSrxScO3 single crystal has been studied by x-ray absorption spectroscopy (XAS). The conduction band is mainly composed of Sc 3d state hybridized with O 2p state. The O 1s XAS spectrum exhibits the existence of the Sc 3d-defect-induced state under the Sc 3d conduction band. The intensity of Sc 3d-defect-induced state increases with Sr substitution. The energy separation between the top of the valence band and the bottom of the Sc 3d-induced unoccupied state is in accordance with the energy gap that is expected from optical absorption. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2999641]

New oligomeric amides were synthesized by the reaction of m-xylylenediamine and dimethyl oxalate to investigate the average molecular weight dependence of the protonic condcutivity. The average molecular weight was determined by the analysis of the Matrix Assisted Laser Desorption / Ionization Time of Flight (MALDI-TOF) mass spectra. The average molecular weight was decreased with increasing the quantity of water in the reaction condition. Some end groups of the oligomers were hydrolysed from the methoxycarbonyl groups to the calboxylic acid groups. The oligomers with the different average molecular weight exhibited different relative humidity (RH) dependence of the protonic conductivity. The protonic conductivity depends on the average molecular weight at the RH of 95%. The difference between the maximum and minimum protonic condcutivity is about three orders of the magnitude. The activation energy for the protonic conduction in one of the oligomers is 0.66 eV. © 2008 Elsevier B.V. All rights reserved.

Epitaxial thin films of 5 mol% Y-doped BaZrO<SUB>3</SUB> (BZY5) proton conducting oxide were fabricated on MgO and Nb-doped SrTiO<SUB>3</SUB> single crystal substrates using PLD method. Crystal structure, microstructure and electrical properties in in-plane and perpendicular directions of those films were studied. BZY5 is grown epitaxially over 700<SUP>o</SUP>C, and its epitaxial relationship is typical "Cube on Cube type". TEM and AFM observations reveal that the films consist of columnar structure. Electrical properties in in-plain direction show significant lower conductivity and higher activation energy than that in perpendicular direction, and the properties are close to that of grain boundary in ceramics, while the electrical properties in perpendicular direction are similar to that of bulk in ceramics. These results suggest that the interfaces between columnar crystals even in epitaxial thin films prevent proton migration as the grain boundaries in ceramics do.

The influence of chemically-induced expansion on the fracture damage of a ceria based solid oxide fuel cell (SOFC) was investigated by using numerial stress analyses. The single cell examined in this study was composed of electrolyte [(CeO_2)_&lt;0.8&gt;(SmO_&lt;1.5&gt;)_&lt;0.2&gt;], anode (Cermets of NiO-20 SDC), and cathode (La_&lt;0.6&gt;Sr_&lt;0.4&gt;Co_&lt;0.2&gt;Fe_&lt;0.8&gt;O_3), respectively. The finite element method was employed to calculate the residual stress, thermal stresses, and chemically-induced expansion stresses for the single cell. The residual and thermal stresses were calculated much smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically-induced expansion stresses were shown to remarkably increase for the temperature range greater than 973K and accounted their magnitude for the primary part of the induced stress. It was shown from the stress analysis that the maximum stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission method. The above-mentioned calculation results suggest that the chemically-induced expansion should be taken into account for the use of ceria based ceramics materials in SOFCs.

The total electrical conductivities of Sr2+ and Al 3+-doped LaScO3 materials, La1-xSr xSc1-yAlyO3 (x = 0.1-0.325, y = 00.01), were examined under wet, dry, reduced and oxidized conditions and were found to express mixed ionic and electronic conductivities. In the high temperature range of 1073 to 1273 K, oxide-ion conduction was predominant. In the systematic measurement of electrical conductivity, we found that the oxide-ion conductivities and activation energies show continuous changes over a wide range of Sr2+ dopant concentrations. We also found that oxide-ion conduction was enhanced by Sr2+ doping to the La 3+ site. The ionic transference number, tion, calculated from the conductivity data under high and low P(O2) conditions was 0.73 (x = 0.325, y = 0.01) at 1273 K.

Gallium and yttrium co-doped BaZrO3 based proton conductors sintered at 1600°C, in which total dopant concentration is fixed at 15mol%, are fabricated using the conventional solid state reaction method. Ga concentration dependence on sinterability and electrical properties are evaluated. Lattice parameter a, relative density and grain size show local maximum at 1mol% Ga concentration, i.e. BaZr0.85Y 0.14Ga0.01O2.925 (BZY14Gal). Relative density of it is over 95%. It is also found that grain boundary conductivity is drastically improved by 1mol% Ga additives. But bulk conductivity becomes slightly lower than that of BZY15 by 1mol% Ga additives. However, total conductivity of BZY14Gal is highest in the specimens due to high grain boundary conductivity and the value is over 2 x 10-3 Scm-1. On the other hand, 3 and 5mol% Ga-doped specimens show significantly low bulk and grain boundary conductivity. So, the results suggest that the Ga additive is effective for sintering at 1600°C, but the range of concentration is very limited. ©The Electrochemical Society.

Artificial superlattices (SLs) of mixed conducting oxides, La0.6Sr0.4FeO3 (LSFO) and La0.6Sr0.4CoO3 (LSCO) have been synthesized on MgO(001) Substrates by Pulsed Laser Deposition (PLD) to investigate the structural effect on their properties as oxide permeable ceramics. To obtain higher epitaxy and better crystallinity of the SL, oxygen partial pressure, Substrate temperature, laser power and repetition rate of the laser have been tuned to optimize the PLD conditions. With the optimized conditions, Reflection High Energy Electron Diffraction (RHEED) oscillation was observed, indicating that the growth of the film is a layer-by-layer process. The thin films of LSFO and LSCO, and the SLs were grown exclusively ill [001] direction of the fundamental perovskite Structure, and the pole figures of those films clearly specify that they are epitaxially grown oil the (001)MgO Substrate. In-plane and out-of-plane lattice constants of LSFO and LSCO layers of the SL have been obtained from ail XRD reciprocal space mapping. The in-plane lattice parameters come closer to each other at a smaller SL period, while the difference in their out-of-plane lattice parameters slightly changes. In this system, therefore, the SL with smaller period is more distorted. The electrical conductivity of the SL is slightly higher than the average value of LSFO and LSCO and is completely different from that of a La0.6Sr0.4Fe0.5Co0.5O3 thin film. (c) 2007 Elsevier B.V. All rights reserved.

The diffusivity of protons in Sr2+-doped LaScO3 single crystals was determined by in-situ infrared absorption spectroscopy. It was found that the high-temperature absorption spectrum shows a broad peak due to O-H stretching bands, which differs from that observed at room temperature. The diffusion coefficient was evaluated by two different methods: (1) suddenly changing the water vapor partial pressure and (2) exchanging H2O and D2O-saturated atmospheres. The diffusion and the activation energy are limited mainly by the diffusivity of oxygen ion vacancies based on the first measurement method at high temperatures. The proton self-diffusion coefficients were obtained by using the second measurement method, and the activation energy is 0.51 eV. (C) 2007 Elsevier B.V. All rights reserved.

The electrical conductivities of Nd1-x Ca (x) Sc1-y Mg (y) O-3 were measured in the temperature range from 673 to 1273 K under both wet and dry conditions. The optimum Ca2+ doping concentration to the Nd3+ site in NdScO3 was found to be the range from 5 to 10%. Hole conduction was predominant under dry and highly oxidized conditions of P(O-2) &gt; 10(-2) kPa in the temperature range from 973 to 1273 K, and proton conduction was predominant under wet and reduced conditions in the temperature range from 673 to 973 K. Oxide ion conduction was predominant under wet and reduced conditions in the temperature range from 1073 to 1273 K. The Mg2+ doping concentration limit for the Sc3+ site to hold a single crystal phase was 2%, and this doping enhanced hole conduction.

The angle-dependent reflectivity of several surface structures was analyzed and evaluated with the viewpoint of solar cell applications. Numerical analysis showed that a Si subwavelength structure (SWS) maintains a lower reflectivity at large incident angles than conventional light-trapping techniques such as a random pyramid texture, and that it can contribute to increasing the output power of solar cells under oblique irradiation. This wide-angle antireflection effect was demonstrated by fabricating test crystalline Si cells with several surface structures including a SWS and measuring their angle-dependent short-circuit current densities.

Systematic investigation of Y-doped BaZrO3 was performed in the point of the relationship between dopant concentration, microstructures, and grain boundary conductivity. As Y concentration increased, average grain diameter increased by 4 times. But the trend of grain boundary character was not changed. Random boundaries were predominant in all samples. Grain boundary conductivity increased by the three orders of magnitude and activation energy was reduced with increasing Y concentration from 5 mol% to 15 mol%. Secondary phase was not observed in the 5 mol% Y-doped BaZrO3. Those results confirmed that contributions of observed parameter to grain boundary conductivity were low. Hence, the contributions of space charge layer was probably high in the Y-doped BaZrO3. (c) 2007 Elsevier B.V. All rights reserved.

Artificial lattices are synthesized by alternate deposition of the SrZrO3 (SZO) and the Y2O3 (SZO/Y artificial lattice) by Pulsed Laser Deposition (PLD) process to investigate the role of dopant cations in the proton migration. The XRD analysis of SZO/Y artificial lattices show that they axe highly oriented in [001] direction epitaxially both on STO(001) and MgO(001) substrates similarly like SZO thin films. The HREM cross sectional views of SZO/Y artificial lattices show that the interface of the SZO layer and Y layer is very flat and the SZO can grow epitaxially even when Y layers are inserted. From the electric conductivity measurements, the main carrier of the SZO/Y artificial lattice is found to be proton. (c) 2007 Elsevier B.V. All rights reserved.

Transparent single crystals of La1-xSrxScCO3 (x=0-0.03) were grown by the floating zone method. The electronic structure near the fundamental absorption edges of these perovskite-type proton conductors was first investigated in the ultraviolet and visible region by optical absorption spectroscopy. The fundamental absorption edge was observed around 5.8 eV. The optical absorption edge around 4.5 eV may be considered to be due to the acceptor level in the band gap. IR absorption spectra suggested that protons occupy intra- or inter-SCO6 octahedral sites. The number of protons at the inter-SCO6 Octahedral sites was found to affect strongly the electrical conductivity. (C) 2006 Elsevier B.V. All rights reserved.

Investigative results of Y concentration dependence of total conductivity, and testing results of self-supported cells, gave us knowledge to realize intermediate temperature operating SOFCs using Y-doped BaZrO3 proton conductors. An increase of Y concentration improved electrical properties of grain boundaries drastically. As a result, total conductivity of a 15mol% Y doped BaZrO3 sample in wet air and wet Ar showed 5mScm(-1) at 400 degrees C. The performance of the self-supported cells was very low because of high electrolyte resistance caused by those thicknesses. Open circuit voltage (OCV) was over 1V in the temperature range of 600 degrees C to 400 degrees C in spite of low ionic transparent number in wet air at 600 degrees C. Degradation of electrolytes was not observed during tests. From those results, electrode-supported cells using Y-doped BaZrO3 Will show sufficient cell performance for intermediate temperature SOFCs.

Dense La0.6Sr0.4CoO3-δfilm electrodes were deposited by pulsed laser deposition (PLD) on Ce0.9Gd0.1O1.95electrolytes. The grain size of one film was 300-500 nm, and the other was 30-50 nm. DC polarization and AC impedance measurements were performed at 873 K-1073 K in O2-Ar gas mixtures. From investigations of the electrochemical capacitances, the rate determining process for both electrodes were confirmed to be the surface reaction. The analyses in the electrochemical resistance revealed that the oxygen adsorption/desorption rate was faster on the electrode with smaller grain size. DC responses agreed with AC results, so the current density on the nano-grain electrode was larger by half an order than those of the sub-micron-grain electrode. Under a dilute oxygen atmosphere, the rate determining step transferred from a surface reaction to a gas phase diffusion. © 2006 Elsevier B.V. All rights reserved.

The grain structure and the electrical conductivity of a Y-doped BaZrO3 perovskite type proton conductor were investigated in terms of preparation method. Powders of Y-doped BaZrO3 were prepared using two methods and were sintered at various temperatures and durations. In this study, grain structures showed no effect in regard to the two preparation methods. The samples which were sintered for a relatively long period showed broad grain diameter distributions (GDD). It was also revealed that most of grain boundaries were assigned as random and this trend was not affected by sintering condition. The bulk and grain boundary conductivities of the sample sintered for long period were significantly lower than those of other samples by more than three orders of magnitude. However, this was not related to differences of grain structure and gain boundary characteristics. (c) 2006 Elsevier BX All rights reserved.

Superlattice thin films of a perovskite-type oxide proton conductor SrZ(r0.95)Y(0.05)O(3)/SrTiO3 were fabricated and their structural and electrical properties were investigated. X-ray and electron diffraction analysis reveals that the thin films were epitaxially gown on MgO (001) substrate. High-resolution transmission electron microscopy observation shows that the multilayered structure is uniform and that the interfaces between the different layers are of low roughness. Misfit dislocations are found at the interface, having Burgers vectors in direction a[100]. From the local elemental analysis, the interdiffusion of Zr and Ti between layers was not observed, while Mg impurities diffused from the substrate are observed. The in-plane electrical conductivity of the thin films was measured by impedance spectroscopy. The conductivity of the superlattices shows a higher value than a single SrZr0.95Y0.05O3 film. The activation energies of the epitaxial layers show relatively higher value than the corresponding single crystal. (c) 2006 Elsevier B.V. All rights reserved.

A partial oxidation test was performed using a La0.6Sr0.4Fe0.8CO0.2O3 (LSFCO6482) membrane in the surface limited conditions at a temperature range of 800-920 degrees C and in a syngas side atmosphere of CH4 diluted with Ar (100%, 25.6% and 1%) in order to investigate chemical stability and oxygen permeation properties. On the surface, deposited carbon was observed in the test and it was revealed to be graphite by an insitu Raman measurement. It was combusted by oxygen fed through the membrane. Segregation of the membrane on both surfaces was observed in all specimens after the test. Moreover, significant decomposition occurred on Air side surface of the membrane which tested in a syngas side atmosphere of 25.6% and 100%. However, the significant decomposition did not affect to be oxygen permeation properties, but it did affect its mechanical strength. (c) 2006 Elsevier B.V. All rights reserved.

Transparent single crystals of La1-xSrxScO3 (x=0.01, 0.03) were grown by the floating zone method. The optical and the electrical properties were studied by infrared absorption spectra and AC-impedance measurements, respectively. Our results showed that proton conduction becomes dominant in La0.97Sr0.03ScO3 single crystals below 700 degrees C. The electrical conductivity increases as the amount of Sr increases. At 600 degrees C, La0.97Sr0.03ScO3 had a proton conductivity of 4.89 x 10(-3) S/cm. This value is almost the same as that in the literature for La0.9Sr0.1ScO3 ceramic samples. It was revealed from infrared absorption spectra that several different sites are occupied by protons in this material. Furthermore, it was found that the intensity of high-frequency O-H bands can be related to the dopant-concentration dependence of the electrical conductivity. (c) 2006 Elsevier B.V. All rights reserved.

A simple mechanical damage testing method, combined with Acoustic Emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells under simulated environments. The damage testing method was applied to ceria electrolyte-supported single cells. The damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damage was most likely due to chemical expansion-induced stresses. It was demonstrated that the AE method enabled us to detect the above-mentioned damage process and to determine the condition for the onset of the damage in the single cell.

A simple fabrication technique for subwavelength structured (SWS) surfaces by means of anodic porous alumina masks directly formed on Si substrates was proposed and demonstrated. By this technique, SWS surfaces were fabricated on polished single-crystalline Si and chemically etched as-cut multicrystalline Si wafers. Smoothly tapered SWS surfaces with a periodicity of 100 nm and a height of 300-400 nm were obtained. A low reflectivity below 1% was observed from 300 to 1000 nm for both of the wafers, in agreement with numerical simulation. After thermal annealing at 800 degrees C, the reflectivity of the SWS surface increased to 3%. (c) 2006 American Institute of Physics.

Spectral properties of two-dimensional (2D) metal surface gratings are investigated to develop high performance solar selective absorbers and sky radiators. Numerical calculations based on rigorous coupled-wave analysis (RCWA) are performed and surface gratings are fabricated on silicon substrates by means of photolithography and etching process. Reflectivity spectra of the samples are measured and they show good spectral selectivity for each application. In order to fabricate surface microstructures in large area with low cost, direct metal imprinting technology are proposed. A microstructured nickel metal mold for the solar selective absorber surface is fabricated by means of electroplating technique and imprint experiments are performed on copper metal surface using mechanical pressing system. As a result, some parts of the surface structures are successfully transferred onto copper substrate.

We set up a high-temperature ellipsometry system for the measurement of optical constants n and k. The n and k values of refractory metals of W and Mo were measured from the visible (VIS) to near infrared (NIR) wavelength range at several temperatures by means of the system. The n drastically increases especially in the NIR region, while the k is almost invariant in all the range with increasing temperatures. Numerical simulation based on rigorous coupled-wave analysis (RCWA) with the values of n and k measured by high-temperature ellipsometry is qualitatively coincident with the measured spectral emissivity at high temperature. It has revealed that spectral emissivity has temperature dependence especially in the NIR region.

Superlattice thin films of the perovskite-type oxide proton conductor SrZr(0.95)Y(0.05)O(3)/SrTiO(3) was fabricated by pulsed laser deposition. Their structural and proton transport properties were reported. X-ray diffraction analysis and selected area electron diffraction revealed that the thin films were epitaxially grown on MgO(001) substrate. High-density edge dislocations and a columnar structure were observed in the films by high-resolution electron microscopy. The in-plane electrical conductivity of the thin films was determined by impedance spectroscopy. The contribution of proton transport to the total conductivity of the films was confirmed by H(2)O/D(2)O exchange measurement. The conductivity of superlattice films was increased by introducing heterointerfaces. The high activation energy (E(a) = 1.0eV) was explained by the grain-boundary effect of the columnar structure in the films.

A simple fracture testing method, which was combined with acoustic-emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells (SOFCs) under simulated environments. The fracture testing method was applied to ceria electrolyte-supported single cells. The fracture damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damages were most likely due to the chemical expansion induced stresses. It was demonstrated that the AE method enabled us to detect the above-mentioned fracture process and determine the condition for the onset of the fracture damage in the single cell.

The influences of the sintering additive content of Y2O3 on elastic modulus of ceria ceramics were investigated by small punch (SP) testing method and molecular dynamics (MD) method. Y2O3 doped ceria powders with a composition of (CeO2)1-x(YO1.5)x (x=0, 0.10, 0.15, 0.20, 0.30, 0.40) were prepared by a co-precipitation method. The powders were compacted by die pressing (50 MPa) followed by cold isostatic pressing (120 MPa), and sintered at 1500°C in air for 5 h. The elastic modulus was decreased significantly with increasing additive contents of the Y2O3 oxides. Especially, it tended to exhibit a minimum value at 10∼20 mol%. However, ionic conductivity increased with increasing additive content of the Y2O3 oxides, exhibited a maximum value at 15 mol%. Calculation model and interatomic potential were shown to be useful to evaluate the elastic property.

The fracture properties of rare earth (yttrium, gadolinium, and samarium) doped ceria ceramics were systematically investigated using the modified small punch method at room temperature in air and at high temperatures in argon gas. The samples prepared by oxalate coprecipitation method showed higher fracture strength than those by solid-state reaction method. In addition, the sintering temperature dependence of gadolinium doped ceria indicated that the highest fracture strength was attained by sintering at 1600 degrees C. Furthermore, it turned out that the fracture strength was influenced by the dopant concentration rather than the kind of dopant. The relationship between mechanical properties and defect structures are discussed from the dopant concentration, sintering temperature and testing temperature dependence of the fracture strength. (c) 2005 Elsevier B.V. All rights reserved.

This paper reviews our recent research on thermal radiation from metallic surface microstructures to develop selective radiators for thermophotovoltaic generation. Numerical simulation showed that two different peaks appeared on the emissivity spectra of metallic gratings. One was originated from surface plasmon polaritons, which was dependent on the grating period and angle. The other peak was explained by the microcavity effect which arose from each microcavity on a grating surface. The microcavity effect became dominant with deepening gratings, and showed suitable properties for selective radiators in thermophotovoltaic generation: a high emissivity within the visible and near-infrared regions, and angle independence. We developed two kinds of two-dimensional metallic gratings based on Si and W with the period of 1.0-2.0 mu m. The W gratings composed of rectangular microcavities displayed a high emissivity in the near-infrared region as expected from the calculation results. It was confirmed experimentally that the W selective radiators have advantages for high-power and high-efficiency thermophotovoltaic systems.

A simple fracture testing method, combined with acoustic-emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells (SOFCs) under simulated environment. The fracture testing method was applied to ceria electrolyte-supported single cells. The fracture damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damages were most likely due to chemical expansion induced stresses. It was demonstrated that the AE method may enable one to detect the above-mentioned fracture process and to determine the onset condition for fracture damage in the single cell.

A creep test was performed on yttria-doped ceria (YDC), which was investigated as an electrolyte for solid oxide fuel cells (SOFC). The test was performed using a four-point bending method and with testing conditions including a constant load under a temperature range of 1050-1125 °C, an applied stress of 20-50 MPa, and an oxygen partial pressure of P(O2)=0.21-10-15.2atm. The results showed that the creep rate increased with decreasing P(O2), and showed a peak at P(O2)=10-13.6atm. The activation energy for creep was increased from 264 to 333 kJ/mol with decreasing P(O2) from 0.21 to 10-14.5atm. These values were much higher than the reported activation energy of oxygen anion diffusion in ceria. Thus, it could be suggested that the creep mechanism is controlled by cation diffusion. The creep mechanism changed from Nabarro-Herring creep to grain boundary sliding in a reducing atmosphere when the P(O2) was lower than 10-14.5atm. © 2004 Elsevier B.V. All rights reserved.

A simple fracture testing method, combined with acoustic-emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells (SOFCs) under simulated environment. The fracture testing method was applied to ceria electrolyte-supported single cells. The fracture damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damages were most likely due to chemical expansion induced stresses. It was demonstrated that the AE method may enable one to detect the above-mentioned fracture process and to determine the onset condition for fracture damage in the single cell.

Spectral properties of one-dimensional tungsten gratings with various depths and widths of grooves were investigated by means of finite-difference time-domain simulation with a multi-Lorentz model. Shallow gratings showed a strong absorption peak due to surface plasmon polaritons when the oscillation of the electric field was parallel to the grating vector. On the other hand, deep gratings with wide grooves showed a different absorption attributed to the microcavity effect when the oscillation of the electric field was perpendicular to the grating vector. With narrowed grooves, another absorption with d-dependence occurred, which was probably due to vertically oscillating surface plasmons to the grooves. © 2005 Optical Society of America.

The mechanical properties and thermal stability of the Al(2)O(3)/Er(3)Al(5)O(12) (EAG) eutectic ceramics have been investigated at very high temperature. The emissive properties of this eutectic ceramics have also been measured and its possibilities of application to an emitter have been discussed. The present eutectic ceramic has excellent high-temperature strength characteristics, showing that tensile yielding stress is approximately 300 MPa at 1650 degrees C and superior thermal stability at 1700 degrees C in an air atmosphere. The present material shows strong selective emission bands at wavelength 1.5 mu m due to Er(3+) ion. The emission bands of this material are nearly coincident with the sensitive region of GaSb PV cell, therefore, the Al(2)O(3)/EAG eutectic ceramic can be regarded as one of the promising emitter materials in TPV systems. (c) 2005 Elsevier Ltd. All rights reserved.

Two-dimensional surface-relief gratings with a period of 1.0-0.2 mum composed of rectangular microcavities were fabricated on single crystalline W substrates to develop spectrally selective radiators for thermophotovoltaic generation. The radiators displayed strong emission in the near-infrared region where narrow-band-gap photovoltaic cells could convert photons into electricity. The enhancement of thermal emission was attributed to the microcavity effect. Power generation tests were carried out and the W gratings showed more than two times higher generation efficiency, compared to a SiC radiator. The results showed that the microstructured W radiators behave as good selective radiator, with both high efficiency and high power density. (C) 2004 American Institute of Physics.

Carbon deposition on a SOFC anode was investigated under direct hydrocarbon fueling condition. Microscopic behaviors were observed with a newly designed sample holder that enabled in-situ observation of an electrode in operation under controlled atmosphere at elevated temperatures. The preferential carbon deposition site, the structure of the deposited carbon, and the chemical or electrochemical re-oxidation processes were investigated with an optical microscope combined with a laser Raman microscope. Color and morphology change of the electrode surface was recorded with a CCD camera, and the deposited materials were identified with a laser Raman microscope. A nickel micro grid was used as a model electrode of a well-defined microstructure. When the cell was kept at an open circuit condition in methane, carbon started to deposit on the surface of Ni grid electrode. The deposition of carbon was clearly observed as the change in the reflection on the nickel surface by optical microscope as well as by the appearance of the specific peak at ∼1560 cm-1 in Raman spectroscopy. The deposited carbon was in the form of graphite on the nickel grid electrode. The carbon coverage on the surface was not uniform but varied from grain to grain. When a certain anodic overpotential (e.g. 200 mV) was applied to the electrode, the carbon disappeared gradually from the edge of the electrode i.e. from the electrode/electrolyte boundary where oxygen was supplied electrochemically. It is the first in-situ observation of the electrochemical carbon oxidation in a real operation condition.

The influences of the sintering additive content of rare-earth oxide (Y2O3, Gd2O3, Sm2O3) on microstructure and mechanical properties of ceria ceramics were investigated by scanning electron microscopy and small specimen technique. A small punch testing method was employed to determine the elastic modulus and biaxial fracture stress of the ceria-based ceramics, and the fracture toughness was estimated by Vickers indentation method. Grain growth in the rare-earth oxides doped ceria ceramics was significantly suppressed, compared to the pure ceria ceramics. However, the elastic modulus, fracture stress and fracture toughness were decreased significantly with increasing additive content of the rare-earth oxides, possibly due to the oxygen vacancies induced by the rare earth oxides doping. The experimental results suggest that the change in the mechanical properties should be taken into account in the use of ceria-based ceramics for solid oxide fuel cells, in addition to the improvement of oxygen ion conductivity. (C) 2004 Kluwer Academic Publishers.

The influences of the sintering additive content of rare-earth oxide (Y_2O_3, Gd_2O_3, Sm_2O_3) on microstructure and mechanical properties of ceria ceramics were investigated by scanning electron microscopy and small specimen technique. A small punch testing method was employed to detemine the elastic modulus and biaxial fracture stress of the ceria-based ceramics, and the fracture toughness was estimated by vickers indentation method. Rare-earth oxides doped ceria powders with a composition of (CeO_2)_&lt;1-x&gt;(RO_&lt;1.5&gt;)_x(R=Y, Gd, Sm and x=0, 0.10, 0.15, 0.20, 0.30, 0.40, 1.00) were prepared by a coprecipitation method. The powders were compacted by die pressing (50MPa) followed by cold isostatic pressing (120MPa), and sintered at 1500℃ in air for 5h. Grain growth in the rare-earth oxides doped ceria ceramics were significantly suppressed, compared to the pure ceria ceramics. However, the elastic modulus, fracture stress and fracture toughness were decreased significantly with increasing additive content of the rare-earth oxides, possibly due to the oxygen vacancies induced by the rare-earth oxides doping. The experimental results suggest that the change in the mechanical properties should be taken into account in the use of ceria-based ceramics for solid oxide fuel cells, in addition to the improvement of oxygen ion conductivity.

The emissive properties of Al2O3/Er3Al5O12 eutectic ceramics have been measured as a candidate of selective emitters. It is identified that the Al2O3/Er3Al5O12 eutectic ceramics have selective emission bands at the wavelength of 1.5 mum, and the emittance at the emission peak is over 0.8. The selective emissive power for GaSb photovoltaic (PV) cells of 49 kW/m(2) is achieved by this material at 1600 K. Since the emission bands match the sensitive region of GaSb PV cells, the Al2O3/Er3Al5O12 eutectic ceramics are suited as emitter materials in thermophotovoltaic (TPV) systems using GaSb PV cells. The optical design of small-scale TPV systems for portable power sources has been investigated with the three-dimensional ray tracing simulation. Using a mirror/PV optical design, the concentrated thermal radiation is irradiated on PV cells with the view factor over 0.75.

The thermophotovoltaic (TPV) research activity in Japan has prospered from the second half of the 90s. In this paper, we will present an overview of TPV research activities in Japan. TPV technologies have been surveyed by research committees in NEDO as a part of the research activity of the New Sunshine Project. The TPV is considered as a new application of non-conventional solar cells, and the situation of TPV technologies, especially TPV cells, in USA and EU is surveyed. Systematic investigative research on TPV systems was performed by ENAA on FY1997 and 1998. In this investigative research on potential market for a TPV power source in Japan has been focused on how TPV can contribute to energy conservation and environmental protection and harmony, compared with conventional engine or turbine generators and underdeveloped power generation technologies such as fuel cells or chemical batteries, etc. In addition to the investigative research, the technical research activities are introduced in this paper.

Mechanical properties of creep rate and fracture strength were investigated on rare earth doped ceria. The samples were prepared by coprecipitation method. and relative density was over 90% for each composition. Creep test of yttria doped ceria (Ce(1-x)Y(x)O(2-x/2)x=0 similar to 0.2) was performed using 4-point bending method under a cons ant load at temperature range of 1050-1125 degrees C. applied stress of 20 similar to 50 MPa and oxygen partial pressure of P(O-2)=0.21-10(-) (15.2) atm. The testing conditions were decided taking into the operating conditions of SOFC. Steady state strain rate calculated from creep curve showed clear oxygen partial pressure dependence. The creep rate increased as decreasing P(O-2) and showed a peak at P(O-2)= 10(-) (13.6) atm. The activation energy of creep was increased from 264kJmol(-1) to 333kJmol(-1) in accordance with P(O-2) decreasing. The activation energy was much higher than reported activation energy of anion diffusion in ceria. So it is concluded that creep control species is cation in air and reduction atmosphere. Since the electrical conductivity and nonstichiometry of this material show similar P(O-2) dependence. the results obtained this work suggest the coincidence between cation and anion diffusion processes in this material. 11 is also found that the creep mechanism of Ce0.8Y0.2O1.9 changed from Nabarro-Heriing creep to grain boundary sliding in reduction atmosphere which P(O-2) was lower than 10(-14.5) atm. Fracture strength of rare earth doped ceria (Ce1-xRxO2-x/2,R=Y,Sm,Gd,x=0 similar to 0.2) was measured by small punch testing method. Test was performed in air at room temperature. Fracture strength showed significant dependence on dopant density, and had a minimum value at x=0.05 and a maximum value at x=0.1. The paper will discuss between the relationship between the mechanical properties and electrical properties on doped ceria.

Spectral properties and thermal stability of two-dimensional (2D) W surface gratings with submicron periodicity are investigated to develop solar selective absorbers for high-temperature applications. Numerical calculations based on the rigorous coupled-wave analysis technique have been performed for simulating the spectral properties of W gratings. The results indicate that the gratings with microcavities have a good spectral selectivity suited for high-temperature applications, while the gratings with micropyramids realize a high solar absorptance over 0.92. 2D surface gratings with submicron holes have been fabricated on W substrates by the fast atom beam etching with highly ordered porous alumina masks. They have shown good spectral selectivity and sufficient thermal stability at 1170 K under a vacuum atmosphere. The observed absorption band is considered to originate from the standing wave resonance between the electromagnetic fields and the standing wave mode generated inside the holes. (C) 2002 Elsevier B.V. All rights reserved.

Nonstoichiometry of the fluorite-type oxide solid solutions Ce1-XYXO2-0.5X-δ(X=0.1, 0.2) was measured as a function of temperature (T=973-1373 K) and oxygen partial pressure (P(O2)=10-2-10-24atm) by means of thermogravimetry. The result shows that the nonstoichiometry of Ce1-XYXO2-0.5X-δ(X=0.1, 0.2) is not explained by a simple point defect model, therefore, defect association models are suggested. From the calculation, it is found that (Ce′CeVÖCe′Ce)xis the major defect association not only in Ce1-XYXO2-0.5X-δ(X=0.1, 0.2), but also in pure CeO2for nonstoichiometries less than 0.10. It is also found that the defect association (Ce′CeVÖCe′Ce)xis dominating at lower temperature and smaller X composition. © 2002 Elsevier B.V. All rights reserved.

We fabricated a two-dimensional subwavelength grating (SWG) on a GaSb substrate. The SWG was patterned by electron-beam lithography and etched by a fast atom beam with SF6 and Cl-2 gases. The SWG consisted of tapered gratings with a 350-nm-period and a 1280-nm-deep groove. The reflectivity at wavelengths from 500 nm to 2300 nm was measured and compared with the results calculated on the basis of rigorous coupled-wave analysis (RCWA). At wavelengths from 500 run to 2000 nm, the SWG decreased the reflection,as much as 5 to 10% from the original value of approximately 40% of the GaSb substrate. The thermal stability of the SWG was also studied by measuring the reflection spectra of heated samples.

The potential market for thermophotovoltaic (TPV) applications has been studied for civilian and industrial sectors in Japan. Comparing the performance of gas engines or turbines, as well as the underdeveloped power generation technologies such as fuel cells or chemical batteries, we have discussed the feasible application field of TPV systems to compete with those power generations. From the point of view of applicability for TPV systems in Japan, portable generators, co-generation systems and solar power plants are selected for our system analysis. The cost and performance targets of TPV systems for co-generation are also discussed by assuming a typical daily profile of electricity and hot water demands in Japanese homes. A progress report on the recent TPV research activities is given as well as a feasibility study concerning such TPV systems in Japan.

As an electrolyte material for reduced temperature solid oxide fuel cell (SOFC), La1-xSrxScO3 - (alpha) (x = 0.05 -0.5) solid oxides with high ionic conductivity were synthesized by the solid phase method. The electrical conductivity rose as the value of x increased. For x greater than or equal to 0.35, the compound underwent a phase transition at 1073K. Adding 2 mol% Al to the Sc site was very effective in suppressing this transition. However, the electrical conductivity of La0.65Sr0.35Sc0.98Al0.02O3 was lower than that of La0.675Sr0.325ScO3. La0.675Sr0.325ScO3, an unstable solid, maintained high ionic conductivity even when effectively stabilized by 1 mol% Al doping at the Sc site. Furthermore, no n-type conduction of La0.675Sr0.325Sc0.99Al0.01O3 was observed under low oxygen partial pressure. (C) 2003 Elsevier Science B.V. All rights reserved.

Spectral emittance and thermal stability of two-dimensional W gratings are investigated to obtain high-temperature resistive selective emitters. Numerical calculations based on rigorous coupled-wave analysis are performed to determine the structural profile of gratings with good spectral selectivity. According to the determined parameters, two-dimensional W gratings composed of rectangular microcavities with the period of 1.0 mum are fabricated on single crystalline and polycrystalline W substrates. The grating shows a strong emission peak which can be explained by the confined modes inside the cavities. The grating with 200 nm wall thickness made from a single crystalline W shows very high thermal stability over 1400 K, while the polycrystalline grating is deformed at a high temperature because of the grain growth. (C) 2003 American Institute of Physics.

We have developed a new measurement technique combining electrochemical measurement with Raman microspectroscopy at high temperatures. In situ observation of carbon deposition on the anode for solid oxide fuel cells was attempted by Raman microspectroscopy. It was found that the form of deposited carbon was amorphous carbon in dry butane/Pt/8YSZ and graphite in humid methane/Ni/8YSZ, respectively. The deposited carbon on Ni surface could not be burned electrochemically.

This work aims to construct the hydrogen-air fuel cells, which operate at intermediate temperature. In order to reduce the operation temperature, the fuel cells are constructed from a thin proton conducting oxide electrolyte and a hydrogen-permeable membrane anode. In this work, we examine at first the applicability of the hydrogen-permeable metal membrane for the anode in the fuel cell. Then, we evaluated the performance of the fuel cells consisting of the thin electrolyte supported by the metal membrane anode. It is recognized that the hydrogen-permeable metal membrane anode works well similar to the porous Ni anode except the voltage loss. The voltage loss for the fuel cell with the Pd anode is lower than that for the fuel cell with the porous Ni anode. BaCe0.9Y0.1O2.95 films, which are used for the electrolyte in the fuel cells, are prepared by the pulsed laser ablation method on the hydrogen-permeable metal substrates used as the anode. The fuel cells with the BaCe0.9Y0.1O2.95 electrolyte of 1.5-2.0 pin thickness and the hydrogen-permeable Pd anode of 25 mum thickness operate stably giving an open circuit voltage of 0.86 V at 400degreesC and the power density of 0.52 mW/cm(2) is derived. (C) 2003 Elsevier B.V. All rights reserved.

The electrical properties of the surface layer formed on Sr (Ti-0.999 Nb-0.001) O-3 single crystal were investigated as a function of oxygen partial pressure and temperature. At room temperature, a high resistive layer was found on the surface of the single crystal with thickness of about 10 mu m after annealing in the air. The resistance of the surface layer is high and insensitive to Po-2 in oxidizing atmospheres, but decreased quickly with decreasing Po-2 in reduced atmospheres at elevated temperature. The resistance decreased when temperature increased up to 1200 degrees C. The fitted activation energy of conduction is about 1.62 eV within 109 Po-2 range from -4.0 to -0.1 below 800 degrees C. This value is near reported activation energy of conduction of the grain boundary in SrTiO3.

Nano-structured perovskite-type proton-conducting thin films have been fabricated by SF6 fast atom beam (FAB) etching, with an ordered anodic porous alumina membrane as a lithographic mask. Period hexagonal structures (100 and 500 M) are patterned on laser ablation-deposited SrCeO3 film on MgO (110) substrate. It is found from X-ray diffraction analysis that the lattice constant a, which is perpendicular to the substrate surface, decreases with decreasing periodicity of the nano-structure. The optical transmission and reflection spectra show typical features of surface-relief grating structures. (C) 2002 Elsevier Science B.V. All rights reserved.

Equivalent circuit analysis was undertaken on a mixed conductor electrode/solid oxide electrolyte system. In a limited case where surface reaction is the predominant rate-controlling process, the equivalent circuit was simplified to parallel connection of a resistor (surface reaction resistance) and a capacitor (chemical capacitance due to oxygen nonstoichiometry). Equilibrium oxygen vacancy concentration was correlated with the chemical capacitance. The model was applied to a dense film of La0.6Sr0.4CoO3-δdeposited on a sintered plate of Ce0.9Gd0.1O1.95by a laser ablation method. Frequency response of the electrochemical impedance was measured under dc bias at 873-1073 K in O2-Ar gas mixtures. The observed capacitance was extremely large, e.g., around 0.1 to 1 F cm-2for the 1.5 μm thick film. The oxygen vacancy concentration in the film was calculated from the capacitance and compared with the literature data measured by thermogravimetry. The film was found to show smaller oxygen nonstoichiometry. The enthalpy for oxygen vacancy formation in the film was about 40 kJ mol-1larger than the bulk. © 2002 The Electrochemical Society. All rights reserved.

We constructed a hydrogen-air fuel cell consisting of proton conducting oxides as an electrolyte and hydrogen storage metals as a hydrogen source. By using the hydrogen storage metals as the hydrogen source, we could test very easily both the electrolyte and the electrode materials. We tested three kinds of proton conducting oxides, i.e. SrCe0.95Yb0.05O2.975, SrZr0.9Yb0.1O2.95 and BaCe0.9Y0.1O2.95 as well as two kinds of the negative electrode materials, i.e. graphite and nickel pastes. The fuel cell operated stably giving open circuit voltages of about 1.2 V, when the cell was maintained near a specific temperature at which hydrogen gas of about 0.1 MPa was released from the hydrogen storage metal. Under load, current densities varied depending on the kind of proton conducting oxides as well as on the negative electrode materials. Also the current densities varied with temperature and the thickness of electrolyte. The best current density-voltage performance was obtained from the fuel cells based on BaCe0.9Y0.1O2.95 and nickel paste. The highest current density at 700 mV, 31.6 mA cm(-2), was delivered by a cell of 0.9 mm electrolyte thickness at 640degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.

A two-dimensional array of a microcavity with a high aspect ratio is made on a Cr-coated Si surface using the micromachining technology. The thermal emission spectra whose wavelength is close to the dimension of cavity aperture (5 mum) are measured on samples with a different aspect ratio. The clear selective emission bands corresponding to the two-dimensionally confined electromagnetic modes are demonstrated experimentally. It is found that the low emissivity of the base material is essential to obtain the high spectral selectivity of thermal radiation. The direction and polarization properties are also examined. The dominant peaks of the emission spectra can be explained by a simple cavity resonator model. (C) 2001 American Institute of Physics.

Local proton dynamics in several kinds of perovskite-type high-temperature protonic conductors were investigated by spectral hole burning spectroscopy. Spectral holes based on light-induced protonic motion were observed. By applying a temperature-cycling technique, the potential barriers for local protonic motion, which is responsible for hole burning, were estimated. The values were several times lower than the activation energies obtained by electric conductivity measurements. The relationship between elementally protonic motion and long-range conduction mechanism is discussed based on these results.

Thermal emissive properties of microstructured surfaces are measured in the near-infrared region. Two-dimensional periodic microstructured surfaces with metal coatings are fabricated with Si anisotropic etching and laser ablation techniques. The structural periods of the samples are 2.0 and 1.5 mum. Clear selective-emission bands are observed experimentally. This selective emission is attributed to the resonance effect between the emissive field and the surface microstructures. In addition, numerical calculation computed with rigorous coupled-wave analysis (RCWA) is performed on the microstructured samples. The selective-emission peaks measured through experiments can be reproduced well by RCWA, and this result suggests strongly that the thermal radiation from periodic structures may have spatial coherence. It is confirmed that the surface microstructure can be applied to the control of spectral emission from high-temperature materials. (C) 2001 Optical Society of America.

Oxygen reaction kinetics was investigated with a dense film of (La,Sr)CoO3-delta on ceria based electrolytes. The rate determining step for a highly Sr doped sample was confirmed to be the surface reaction that included at least two series processes, i.e. oxygen adsorption from the gas phase and oxygen transfer across the sub surface layer of the electrode. The reaction rates of those processes were determined separately by using a porous oxygen sensor (POS) which measures the surface oxygen potential on the working electrode. Empirical equations and the kinetic parameters were obtained. The sub surface oxygen transfer process had higher activation energy, and became important in lower temperature applications.

Thermal emissive properties of microstructured surfaces are measured in the near-infrared region. Two-dimensional periodic microstructured surfaces with metal coatings are fabricated with Si anisotropic etching and laser ablation techniques. The structural periods of the samples are 2.0 and 1.5 μm. Clear selective-emission bands are observed experimentally. This selective emission is attributed to the resonance effect between the emissive field and the surface microstructures. In addition, numerical calculation computed with rigorous coupled-wave analysis (RCWA) is performed on the microstructured samples. The selective-emission peaks measured through experiments can be reproduced well by RCWA, and this result suggests strongly that the thermal radiation from periodic structures may have spatial coherence. It is confirmed that the surface microstructure can be applied to the control of spectral emission from high-temperature materials. © 2001 Optical Society of America.

Phase diagram calculations that were made previously for the ZrO2-MOm/2(m = 2, 3, 4) systems and for the ZrO2-YO1.5-MOm/2 (M = transition metals) systems have been extended to the ZrO2-YO1.5-CeO2(-CeO1.5) system to make an attempt to explain (1) thermogravimetric (TG) results as a function of oxygen potential, (2) electronic conductivity as a function of oxygen potential, and (3) a miscibility gap observed in air. The interaction parameters for the CeO2-CeO1.5-YO1.5 system were obtained from the reported oxygen nonstoichiometry in CeO2-x and rare earth doped ceria, (Ce,RE)O2-δ. The interaction parameters for the ZrO2-CeO2 subsystem were obtained so as to reproduce the observed miscibility gap at 1273 K. Those thermodynamic properties can reproduce consistently the experimental behaviors of the electronic conductivity and the TG results in the (Zr1-xCex)0.8Y0.2O1.9 solid solutions these indicate the enhancement of reduction of CeO2.

Local proton dynamics in several kinds of perovskite-type high-temperature protonic conductors were investigated by spectral hole burning spectroscopy. Spectral holes based on light-induced protonic motion were observed. By applying a temperature-cycling technique, the potential barriers for local protonic motion, which is responsible for hole burning, were estimated. The values were several times lower than the activation energies obtained by electric conductivity measurements. The relationship between elementally protonic motion and long-range conduction mechanism is discussed based on these results.

An ordered anodic porous alumina membrane has been used as a lithographic mask of SF6 fast atom beam etching to generate a 100 nm period antireflection structure on a silicon substrate. The antireflection structure consists of a deep hexagonal grating with 100 nm period and aspect ratio of 12, which is a fine two-dimensional antireflection structure. In the wavelength region from 400 to 800 nm, the reflectivity of the silicon surface decreases from around 40% to less than 1.6%. The measured results are explained well with the theoretical results calculated on the basis of rigorous coupled-wave analysis. (C) 2001 American Institute of Physics.

The emissive properties of Al2O3/Er3Al5O12 eutectic composite were measured in the temperature range of 1000 to 1700 K. It was confirmed that the Al2O3/Er3Al5O12 eutectic composite has selective emission bands at a wavelength of 1.5 μn attributable to Er3+ ions. It is found that the intensity obeys the T4-law. The emittance of over 0.8 is observed in the selective region. Since these emission bands match up the sensitive region of the GaSb PV cell spectrally, the Al2O3/Er3Al5O12 eutectic composite is a suitable emitter material for using in thermophotovoltaic generation systems. The effects of temperature and thickness on the selective emission efficiency have been studied and discussed. © 2000 The Japan Society of Applied Physics.

Ceria doped yttria stabilized zirconia (ZrO2-CeO2-Y2O3 system) shows electron-ion mixed conduction at high temperatures under a reduced atmosphere. In this system, the electronic conductivity is caused by electrons, which may diffuse by hopping conduction between Ce4+ and Ce3+. We applied the electronic Raman scattering technique on the system in older to measure the concentration of Ce3+ in samples. For the X = 0.6 and 0.8 samples in [(ZrO2)(t-X) (CeO2)(X)](0.9)(Y2O3)(0.1), the oxygen partial pressure dependence of the electronic Raman intensities agrees well with that of the oxygen non-stoichiometry measured by thermogravimetry. From this result. it is confirmed that all of the introduced electrons at reduced condition are trapped at cerium centers in these materials. (C) 2000 Elsevier Science B.V. All rights reserved.

A mixed conductor, ZrO2-CeO2-Y2O3 (Ce-YSZ), exhibits anomalous electrical properties depending on oxygen partial pressure and CeO2 concentration. We measured surface reaction rates and oxygen tracer diffusion coefficients of YSZ with various CeO2 concentrations by secondary ion mass analyses. The Ce concentration dependence of oxygen tracer diffusion coefficient in air corresponds with that of the total electrical conductivity, over which the ionic conductivity is dominant. The surface exchange coefficient, however, had a higher value in the region of 20 similar to 60 mol% CeO2 containing YSZ compared to other compositions. Ce-YSZ, which contains this region of CeO2 concentration, exhibits high electronic conduction at reducing conditions. The ionic and electronic conductivities are considered to affect the oxygen tracer diffusion coefficient and the surface exchange coefficient, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.

High temperature proton conducting oxides having distorted-perovskite structure show high protonic conduction at elevated temperatures, and have been applied in the sensors and energy conversion devices. In order to control the distortion of crystal structure, we have fabricated SrZrO3-SrCeO3 superlattices (SLs) by laser ablation technique and have investigated the structural and electrical properties. The epitaxial growth on MgO (110) substrates is confirmed from 4-axis X-ray diffraction analysis. From the dependence of lattice constant on superlattice periodicity, it is confirmed that critical periodicity make strained superlattice is about 15-20 nm for system SrZrO3/SrCeO3 on MgO (110). (C) 2000 Elsevier Science B.V. All lights reserved.

Nonstoichiometry of fluorite-type oxide solid solutions Zr0.164Ce0.654Y0.182O1.91 - δ was measured as a function of temperature (T = 973-1273 K) and oxygen partial pressure (P(O2) = 10-2-10-24 atm) using thermogravimetry. The experimental date was well reproduced by the regular solution model. From the δ-logP(O2)-T relationship, the partial molar enthalpy (ho-ho̊) and the partial molar entropy (so - so̊) of oxygen in Zr0.164Ce0.654Y0.182O1.91 - δ were also determined as a function of δ. The (so-so̊) agrees well with theoretical calculation using the random configuration. The δ dependence of (ho-ho̊) can be attributed to origin of the deviation from ideal solution behavior of this system.

A dense film of La0.6SrCoO3-delta was fabricated on a Ce0.9Gd0.1O1.95 electrolyte pellet by a laser ablation method. Electrochemical measurements were performed using a three-terminal cell, and at the same time, the oxygen potential on the electrode surface was monitored by a potentiometric method. A porous ceria pellet with a platinum electrode on one side (porous oxygen sensor: POS) was put on the electrode surface as a surface oxygen potential probe. The ac response of POS was analyzed as pseudo impedance in a complex impedance plane. Although the impedance of the three-terminal cell had two kinds of responses, i.e. high frequency response due to the grain boundary impedance and a low frequency response due to the electrochemical impedance, POS responded only in the frequency range of the electrochemical impedance. The magnitude of the POS response was close to that of the three-terminal impedance in that frequency range, suggesting that the electrode overvoltage is mostly due to the slow dissociative adsorption of oxygen and the resulting non-equilibrium oxygen potential at the electrode surface.

Parabolic dish systems equipped with optical fiber transmission of highly concentrated solar energy can provide a stationary high temperature or high photon density point to us. This is very useful for the applications of solar thermal utilization system, for example solar chemistry on terrestrial or heat source in space. However, the solar energy density sharply decreases form at the end point of the optical fiber, because the transmitted solar light disperses from the exit of the optical fiber according to its numerical aperture. To overcome this problem, we are investigating the CPC (Compound Parabolic Concentrator) coupled to the exit of an optical fiber. This method is capable of increasing the solar energy density emitted from optical fibers. In this paper, we report the experimental results from transmission of solar energy concentrated by a parabolic concentrator through an optical fiber bundle coupled with CPC. Comparing the spatial energy distribution at the CPC exit with that at the entrance of CPC, it is demonstrated that the density of thermal flux is increased about 3.6 times by CPC.

Transparent solid solution crystals of Sr[CeZr]0.95Yb0.05O3 were grown by the FZ-method using a Xe-arc imaging furnace to investigate proton conductivity in mixed perovskite-type oxides. It is observed that there are at least five different O-H stretching vibrational modes in these solid solutions and their intensities and peak wave numbers depend on the composition of Ce and Zr. The results of electrical conductivity showed that these materials are proton conductors as well as SrCe0.95Yb0.05O3 and SrZr0.95Yb0.05O3. The IR-absorption intensity and the electrical conductivity have their maxima at x = 0.8 in Sr[CexZr1-x]0.95Yb0.05O3. The Raman spectra of solid solutions suggest that the lattice distortion was changed by addition of SrZr0.95Yb0.05O3 to SrCe0.95Yb0.05O3.

The removal of carbon dioxide from flue gas is one of the most important issues for preventing a greenhouse effect. An alkanolamine in aqueous solution absorbs CO2and is regenerated by CO2recovery in the temperature range from 100 to 120°C. In order to obtain the energy for CO2recovery, we are studying for solar energy utilization as a heat source for CO2recovery process. This temperature range can be obtained using a stationary trough-type concentrator. We designed and fabricated CO2recovery system which consists of an integrated stationary evacuated concentrator and an amine regenerator. CO2was successfully recovered using this system, and the system performance and properties of amine regeneration process were evaluated. The solar collecting area required for CO2recovery was also evaluated.

Superlattices of perovskite-type proton conductors, SrCeO3, SrZrO3 and SrTiO3 were synthesized by pulsed laser ablation method to study the effect of lattice distortion on proton dynamics. The SrCeO3, SrZrO3 thin films and their superlattices are grown in the [100] azimuth when they are fabricated on MgO(100) substrate and in the [211] azimuth when they are fabricated on SrTiO3(100) substrate or MgO(100) substrate with buffer layer of SrTiO3. XRD and Raman results suggest that the lattice distortion depends on the thickness ratio of the superlattice.

Oxygen isotope exchange experiments were carried out with a dense La0.6Sr0.4CoO3-δfilm (0.5 μm thick) deposited on a Ce0.9Ca0.1O1.9substrate by a laser ablation method. The isotope exchange profile was measured from the surface into the electrolyte by a secondary ion mass spectrometer (SIMS). The oxygen diffusion through the La0.6Sr0.4CoO3δfilm was fast enough not to make any observable gradient in oxygen isotope concentration inside the film. The surface isotope exchange rate, k*, was calculated from the diffusion profile into the electrolyte layer. The electrochemical impedance, σE, was compared with k*. The oxygen partial pressure dependence of those two parameters were quite similar. The absolute value of k* was larger than expected from σEby a factor of 2 or higher.

We applied functionally graded materials to anode of SOFC to keep good adherence at electrolyte/electrode interface. We investigated CeO2 doped YSZ mixed conducting films, in which Ce concentration was graded, fabricated by laser ablation method. Mixed conduction is exhibited at high Ce concentration in the film, and the same mechanical and electrical properties as the electrolyte are exhibited al low Ce concentration. In this study, the structural and the electrical properties of the films were measured.

Oxygen transport in nominally pure and weakly transition metal- or Ce-doped yttria-stabilized zirconia (9.5 mol% Y2O3) has been investigated by a contactless (optical) relaxation technique at temperatures between 950 K and 1100 K and oxygen partial pressures 10(-20) bar less than or equal to p(O2) less than or equal to 1 bar. The chemical diffusion coefficient of oxygen ((D) over tilde) is strongly influenced by the trapping reaction of minority charge carriers, electrons at p(O2) less than or equal to 10(-10) bar and electron holes at higher partial pressures, at specific impurity sites, notably Ti and Ce defects stabilized by oxygen vacancies. Its temperature and oxygen partial pressure dependence can be quantitatively described by a generalized ambipolar transport model. Re-analysis of the literature (D) over tilde-values provides further evidence of the impurity control of the chemical diffusion coefficient and the optical absorption in the visible range. Especially the unusually large scatter of (D) over tilde in nominally pure material call be easily explained on this basis. Model calculations for the (D) over tilde-behaviour of the two trap system YSZ:Ti/Ce are presented and an energy level diagram of the latter system is proposed.

Porous and dense La0.6Sr0.4CoO3-delta layers were prepared as working electrodes on 10 mole% CaO doped CeO2 electrolytes. Electrochemical measurements were made as a function of oxygen partial pressure at 500 to 900 degrees C. The electrode interface conductivity and the steady-state polarization curve suggested that the reaction rates with porous electrodes are controlled by gas diffusion process at low P(O-2) and those with dense electrodes by surface reaction.

Persistent spectral hole burning (PSHB) has been observed at 110 K in EU(3+) exchanged Nai beta'-alumina crystals. This is the highest burning temperature for PSHB in EU(3+) doped materials. It is found that the long lived holes at high temperature are caused by light-induced local motion of ions surrounding the EU(3+) ions. The results both of hole relaxation and temperature cycling measurements can be well interpreted by a hopping model with a Gaussian distributed barrier height.