CHEMICAL THERMODYNAMIC CONSIDERATIONS IN SINTERING OF LACRO3-BASED PEROVSKITES

The thermodynamic properties of LaCrO3 and related compounds have been estimated and utilized to correlate sinterability with phase relations in the La-M-Cr-O (M = Mg,Ca,Sr) systems. Chemical equilibria calculations reveal that calculated vapor pressures of gaseous chromium oxides (especially CrO3) can be well correlated with our previous experimental results on sinterability. The poor sinterability can be ascribed to the formation of a thin layer of Cr2O3)s) which is formed from incongruently vaporized CrO3(g) at the interparticle neck during the initial stage of sintering in air. Improvement of sinterability of Cr2O3-based oxides can be achieved by removing this Cr2O3 layer or by decreasing CrO3(g) vapor pressure to prevent the formation of Cr2O3 layer. These suggest that (La1-(x)Ca(x))CrO3 perovskites are the most suitable materials for high sinterability, since these materials have the low CrO3 vapor pressure without precipitation of La2O3.