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N. Sakai, T. Kawada, H. Yokokawa, and M. Dokiya
[J. of the Ceramic Soc. of Japan, Vol.101, No.11, pp.1195-1200, 1993]
The effect of preparation method on the chemical stability of sinterable (La,Ca)CrO_{3-δ} powder was investigated. The ceramic method (powder mixing method) resulted in inhomo-geneous distributions of the calcium content (x) in the perovskite phase (La_{1-x} Ca_{x} CrO_{3-δ) after calcining at a temperature from 1223 to 1373K. More homogeneous powder was obtained by the liquid mixing method. The distribution of calcium content caused a large amount of second phases such as calcium oxychromates (Ca_{m}(CrO_{4})_{n}) in a powder prepared by the ceramic method, and an excess amount of the second phase remained as Ca_{5}(CrO_{4})_{3}OH on the surface of the ceramic after sintering at 1573K. During a treatment in an H_{2}+H_{2}O gaseous mixture at 1273K for 627h, Ca_{m}(CrO_{4})_{n} decomposed to CaO and α-CaCr_{2}O_{4}, and the decomposition was enhanced by the existence of silicon-containing impurities. The liquid mixing method minimized the amount of Ca_{m}(CrO_{4})_{n}, and resulted in sufficient chemical stability in H_{2}+H_{2}O.