On the formation mechanism of BaTiO3-BaZrO3 solid solution through solid-oxide reaction

The formation of solid solution composition BaTi0.6Zr0.4O3, from BaCO3, TiO2 and ZrO2 powders has been studied through solid-oxide reaction using TGA/DSC, XRD. BaCO3 decomposes at much lower temperature in the mixture due to the presence of TiO2. BaTiO3 (BT) and BaZrO3 (BZ) start forming from the temperature range 700-800 °C without intermediate formation of BaO or other titanate/zirconate phases. Rate of BaTiO3 formation is higher than BaZrO3 formation due to the lower activation energy (34.3 kcal/mol) required for titanate formation than zirconate (48.4 kcal/mol). Solid solution then forms by diffusion of BaTiO3 into BaZrO3 from 1300 °C onwards. Lattice parameter of initial SS phase is higher, indicating the phase has a coherent interface with zirconate and higher in Zr-concentration than the final product. Activation energy for the SS formation (133 kcal/mol) indicates that Ba and/or O diffusion through SS layer may limit the reaction.