Sol-gel synthesis of lanthanum chromite powder

Alkaline earth-doped LaCrO 3 is a satisfactorily conducting ceramic material for the interconnector of Solid Oxide Fuel Cells (SOFC). For the synthesis of highly sinterable LaCrO 3 powders spraydrying of adequate precursors like sols based on alkoxides has been used. Lanthanum chromium hydroxide sol was prepared by hydrolysis of synthesized methoxide complexes. The chemical reactions during hydrolysis and peptization of the precursors are described. The crystalline phase formation during heat treatment of spray-dried amorphous gel consisting of hydroxides and contaminant chloride ligands was characterized by thermal analysis methods (TG, DTG, DTA) and X-ray diffraction analysis. The progressive oxidation of Cr(III) by thermal dehydroxylation transforms the powder into fine crystallized La(III) Cr(V)hydroxo-oxychloride at 450 °C. A thermal treatment permits complete chlorine removal forming sinterable crystalline LaCrO 3 perovskite powder at temperatures above 720 °C. The same sol-gel process also can be applied to chlorine-free nitrate-containing alkoxide sols. The properties of sinterable lanthanum chromite powders obtained from these sols are compared with powders made by direct spray-drying of lanthanum-chromium nitrate solutions.