Yoshiko Hiei

Thermal-expansion behaviors and mechanisms for Ca- or Sr-doped lanthanum manganite perovskites under oxidizing atmospheres

The thermal expansion behavior and mechanism of A-site-deficient lanthanum manganite perovskites, La{sub 1{minus}x}MnO{sub 3} (0 < x {le} 0.1), and alkaline earth metal (AE)-doped lanthanum manganite perovskites, La{sub 1{minus}x}AE{sub x}MnO{sub 3} (AE = Ca and Sr, 0 {le} x {le} 0.4), under oxidizing atmospheres have been investigated. The average linear thermal expansion coefficients of the AE-doped lanthanum manganites decreased with increasing Ca content up to 20 mol % and with increasing Sr content up to 10 mol %, and then increased. During the thermal cycle measurement, the La{sub 1{minus}x}MnO{sub 3} (0 {le} x {le} 0.1) perovskite samples and the La{sub 1{minus}x}AE{sub x}MnO{sub 3} perovskites (0 {le} x {le} 0.3) shrank, while no anomalous shrinkage behavior was observed for the La{sub 0.6}AE{sub 0.4}MnO{sub 3} samples. From the results of high-temperature X-ray diffraction analysis, no dependency of cell volume of the perovskites on aging time at selected temperatures and on thermal cycles was observed.

Sintering behavior of Ca- or Sr-doped LaCrO3 perovskites including second phase of AECrO4 (AE=Sr, Ca) in air

Abstract The sintering characteristics and mechanisms of stoichiometric alkaline earth metal (AE)-doped lanthanum chromites, including the second phase of AECrO4 with low-melting point in air, (La1−xAExCrO3, AE=Ca and Sr, 0≤x≤0.3), have been discussed. When x≤0.2, the sintering properties of La1−xCaxCrO3 are lower than those of La1−xSrxCrO3. However, the reverse results were observed at x=0.3. The mixtures of LaCrO3 and AECrO4 showed low sintering properties. It was found that the reaction of the second phases with LaCrO3 started at temperatures lower than the melting point. Thermal expansion coefficients (TECs) in the temperature range from 50 to 1000°C were 8.6×10−6/°C for LaCrO3, 13.1×10−6/°C for CaCrO4, and 17.5×10−6/°C for SrCrO4. The second phases with larger TEC among the LaCrO3 particles disturb the sintering characteristics of the LaCrO3 particles during the high temperature heat treatment.

Sintering behavior and mechanism of Sr-doped lanthanum chromites with A site excess composition in air

Abstract Sintering characteristics and mechanisms of lanthanum strontium chromites, (La 1− x Sr x ) 1+ y CrO 3 (0≤ x ≤0.3, 0≤ y ≤0.02), in air are discussed in comparison with the results for Ca-doped lanthanum chromites. The sinterability of La 0.9 Sr 0.1+ y CrO 3 increased with increasing alkaline earth (AE) content, but was much lower than that of La 0.9 Ca 0.1+ y CrO 3 . It was found that the ratios of AE to Cr formed a second phase in the sample in the region 0.5 x x 0.9 Sr 0.1 CrO 3 with 2 mol% sintering aid was clarified. With increasing ionic field strength, that is with decreasing basicity, the relative density of the doped La 0.9 Sr 0.1 CrO 3 perovskites decreased.

Evaluation of Ni and Ti-doped Y2O3 stabilized ZrO2 cermet as an anode in high-temperature solid oxide fuel cells

Abstract The compatibility of nickel and Ti-doped 8 mol% Y 2 O 3 stabilized ZrO 2 (Ni–Ti–YSZ) cermets has been discussed for use as an anode in high-temperature solid oxide fuel cells (SOFC). The solubility limit of TiO 2 in the YSZ fluorite was estimated to be at least 10 mol%. With increasing Ti content in the Ti–YSZ samples, the average linear thermal expansion coefficient was found to decrease when measured in an H 2 atmosphere. In an H 2 atmosphere, the oxygen vacancy concentration was observed to increase with increasing Ti content and temperature, and its value in the 8 mol% Ti-doped YSZ (8Ti–YSZ) sample was 0.0056 at 1000 °C. Although electronic conduction appeared in the Ti–YSZ samples at temperatures greater than ∼600 °C in the H 2 atmosphere, their electrical conductivities had a tendency to decrease with increasing Ti content. The mechanical strength of the Ni–Ti–YSZ cermets at room temperature were found to increase with increasing Ti content. Anodic polarization of the 40 vol.% Ni–8Ti–YSZ cermet at 1000 °C was 60 mV at 300 mA cm −2 in the H 2 atmosphere after firing at 1400 °C for 10 h.

Thermal expansion of La1−xSrxCrO3−δ

Abstract Thermal expansion coefficients of La 1− x Sr x CrO 3 and reduced La 1− x Sr x CrO 3− δ were measured using a push-rod type dilatometer in the temperature range from 100 to 873 K. The thermal expansion coefficient increased and the temperature of structural transition from orthorhombic to rhombohedral decreased with the increase of Sr content. Magnetic transition temperature decreased with the decrease of Cr 3+ content in La 1− x Sr x CrO 3− δ . The doping effect of Sr in La 1− x Sr x CrO 3 on the thermal expansion was discussed using molecular dynamics simulation.