Thermal analysis and prediction of phase equilibria in the TiO ₂-Bi₂O₃ system

A thermodynamic study on the TiO₂-Bi₂O₃ system was carried out using differential thermal analysis (DTA) and X-Ray diffraction (XRD) techniques covering the composition range from 65 to 90 mol% Bi₂O₃. From the XRD results the only two intermediate compounds in the Bi₂O₃ rich region were Bi ₄Ti₃O₁₂ and Bi₁₂TiO₂₀. The Bi₄Ti₃O₁₂ phase presents the well known plate-like morphology. The experimentally determined phase transition temperatures with DTA technique were compared with thermodynamic calculated results and good agreement was obtained. The DTA results also showed that the limit of the peritectic reaction between liquid and Bi₄Ti ₃O₁₂ occurs approximately at 90 mol% Bi₂O ₃. The phase diagram of the TiO₂-Bi₂O ₃ system was calculated using a quasichemical model for the liquid phase. The thermodynamic properties of the intermediate compounds were estimated from the data of TiO₂ and Bi₂O₃ pure solids. In this manner, data for this binary system have been analysed and represented with a small adjustable parameter for the liquid phase.