XPS AND SEM STUDIES OF CA-SUBSTITUTED AND NI-SUBSTITUTED LACRO(3) AFTER QUENCHING FROM REDUCING AND OXIDIZING ATMOSPHERES AT 800-DEGREES-C

Sintered and polished samples of La1-xCa(x)CrO3 (x = 0.0, 0.1, 0.3, 0. 5) and La1-xCa(x)Cr1-yNi(y)O3(x = 0.3, y = 0.05) were annealed and que nched under reducing or oxidizing conditions at 800-degrees-C and anal ysed with XPS and SEM. After annealing in H2 + H2O the surfaces of the samples with x = 0.3 and x = 0.5 were enriched in Ca in a 5 nm deep z one. Cr was not enriched and was present in the + 3 state. Annealing i n O2 + H2O gave Ca enrichment and crystalline outgrowths, increasing w ith increasing Ca contents. The Cr in the surface was in the + 3 and 6 states, and the amount of Cr6+ increased with increasing Ca content s. These observations are assigned to precipitation of CaCrO4 and poss ibly other phases. The Ni-doped sample exhibited less grain growth dur ing sintering and less surface recrystallization in oxidizing atmosphe res than the corresponding sample without Ni.