resumo
The equilibrium chemical strains induced by the oxygen hyperstoichiometry variations in mixed-conducting La(2)Ni(1-x)M(x)O(4+delta) (M = Fe, Co, Cu; x = 0-0.2) with K(2)NiF(4)-type structure, were studied by controlled-atmosphere dilatometry at 923-1223 K in the oxygen partial pressure range 5 x 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 (epsilon(C)) is less than 0.02%. The ratio between these values and the corresponding nonstoichiometry increment varies from -3 x 10(-3) to 6 x 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) x 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 K(2)NiF(4)-type lattice, namely the opposing variations of the unit-cell parameters on changing oxygen stoichiometry.
palavras-chave
OXYGEN-ION CONDUCTORS; FORMER SOVIET-UNION; THERMAL-EXPANSION; TRANSPORT-PROPERTIES; CERAMICS; OXIDES; DIFFRACTION; BEHAVIOR; METHANE; ELECTROCHEMISTRY
categoria
Chemistry; Materials Science
autores
Kharton, VV; Kovalevsky, AV; Avdeev, M; Tsipis, EV; Patrakeev, MV; Yaremchenko, AA; Naumovich, EN; Frade, JR
nossos autores
Aleksey Yaremchenko
Investigador Principal
Andrei Kavaleuski
Investigador principal
Jorge Ribeiro Frade
Professor(a) Jubilado(a)