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

Abstract

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 and BaZrO3 start forming from the temperature range 700o-800oC 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 1300oC onwards. Lattice parameter of initial SS-phase is higher, indicating the phase has a coherent interface with zirconate and higher in Zr-concentration than final product. Activation energy for the SS-formation (133 kcal/mole) indicates that Ba and/or O diffution through SS layer may limit the reaction.