XPS and SEM studies of Ca- and Ni-substituted LaCrO sub(3) after quenching from reducing and oxidizing atmospheres at 800 degree C

Sintered and polished samples of La sub(1-x)Ca sub(x)CrO sub(3) (x identical with 0.0, 0.1, 0,3, 0.5) and La sub(1-x)Ca sub(x)Cr sub(1-y)Ni sub(y)O sub(3) (x identical with 0.3, y identical with 0.05) were annealed and quenched under reducing or oxidizing conditions at 800 degree C and analyzed with XPS and SEM. After annealing in H sub(2)+H sub(2)O the surfaces of the samples with x identical with 0.3 and x identical with 0.5 were enriched in Ca in a 5 nm deep zone. Cr was not enriched and was present in the +3 state. Annealing in O sub(2)+H sub(2)O gave Ca enrichment and crystalline outgrowths, increasing with increasing Ca contents. The Cr in the surface was in the +3 and +6 states, and the amount of Cr super(6+) increased with increasing Ca contents. These observations are assigned to precipitation of CaCrO sub(4) and possibly other phases. The Ni-doped sample exhibited less grain growth during sintering and less surface recrystallization in oxidizing atmospheres than the corresponding sample without Ni.