THERMODYNAMIC STABILITY OF THE LITHIUM ZIRCONATES AND LITHIUM YTTRATE

The thermodynamic data of the lithium zirconates (Li2ZrO3, Li6Zr2O7, Li4ZrO4 and Li8ZrO6) were calculated based on the Neumann-Kopp rule and the third law. The equilibrium lithium oxide vapor pressures and lithium loss values due to evaporation at different temperatures and in different environments were obtained. Thermal decomposition of Li8ZrO6 was assessed by theoretical calculations and weight loss and XRD experiments. The experimental results are in agreement with the theoretically predicted ones. The Gibbs free energies of reaction of lithium zirconates and lithium yttrate with water vapor and the corresponding equilibrium vapor pressures of water were calculated. The stability of pure and yttrium-doped Li8ZrO6 with respect to water vapor is assessed from weight gain measurement in air.