Chemically induced expansion of La2NiO4+ δ-based materials

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American Chemical Society
The equilibrium chemical strains induced by the oxygen hyperstoichiometry variations in mixed-conducting La2Ni1-xMxO4+δ (M = Fe, Co, Cu; x = 0−0.2) with K2NiF4-type structure, were studied by controlled-atmosphere dilatometry at 923−1223 K in the oxygen partial pressure range 5 × 10-4 to 0.7 atm. In combination with the oxygen content measured by coulometric titration and thermogravimetry, the results reveal a very low chemical expansivity, favorable for high-temperature electrochemical applications. Under oxidizing conditions, the isothermal expansion relative to atmospheric oxygen pressure (εC) is less than 0.02%. The ratio between these values and the corresponding nonstoichiometry increment varies from −3 × 10-3 to 6 × 10-3, which is much lower compared to most permeable mixed conductors derived from perovskite-like cobaltites and ferrites. Consequently, the chemical contribution to apparent thermal expansion coefficients at a fixed oxygen pressure, (13.7−15.1) × 10-6 K-1, does not exceed 5%. The high-temperature X-ray diffraction studies showed that this behavior results from strongly anisotropic expansion of the K2NiF4-type lattice, namely the opposing variations of the unit-cell parameters on changing oxygen stoichiometry. © 2007, American Chemical Society
Oxides, Membranes, Oxygen, Ceramics, Stoichiometry, Electrochemistry, Thermal gravimetric analysis, Thermal expansion
Kharton, V. V., Kovalevsky, A. V., Avdeev, M., Tsipis, E. V., Patrakeev, M. V., Yaremchenko, A. A., Naumovich, E. N., & Frade, J. R. (2007). Chemically induced expansion of La2NiO4+ δ-based materials. Chemistry of Materials, 19, 8, 2027–2033. doi:10.1021/cm070096x