Low temperature synthesis of calcium cobaltites in a solid state reaction

This paper presents synthesis of calcium cobaltites of the nominal composition of Ca^sub 3^Co^sub 4^O^sub 9^ prepared by the solid state reaction. The reaction between CaCO^sub 3^ and Co^sub 3^O^sub 4^ was investigated at 700-900 °C during 20 h and at 800 °C during 2-30 h. Mass changes, phase composition and Co^sup +3^, Co^sup +4^ content were examined. Stability of the calcined specimens was tested by DTA/TG. It was found that two phases: Ca^sub 3^Co^sub 4^O^sub 9^ and Ca^sub 3^Co^sub 2^O^sub 6^ were present as a result of calcinations above 800 °C. On the other hand, the temperature of 750 °C was too low for calcium cobaltites to be synthesized. Mono-phase material with Ca^sub 3^Co^sub 4^O^sub 9^ phase was obtained after calcinations at 800 °C but non-stoichiometry of the compound and its relation to the calcinations time were found. Once synthesized, the compound was stable up to 900 °C.[PUBLICATION ABSTRACT]