Synthesis of Bi4Ti3O12 by high energy milling of Bi2O3–TiO2 (anatase) mixtures

The mechanism of Bi4Ti3O12 formation starting from the two constituent oxides has been studied. Starting from a physical mixture, a solid-state reaction occurs between the two oxides that leads at ≈700 °C to a mixture of the two ternary oxides Bi12TiO20 + Bi4Ti3O12 along with unreacted precursor oxides. At T ≈ 830 °C Bi12TiO20 reacts with TiO2 forming Bi4Ti3O12 and, finally, at T ≈ 850 °C, the residual Bi12TiO20 undergoes the peritectic reaction that produces Bi4Ti3O12 plus a liquid phase. However, the formation of Bi4Ti3O12 is not complete at temperatures as high as 900 °C. Starting from a mechanically activated mixture, the intermediate Bi12TiO20 only forms as a minority phase at a lower temperature (T ≈ 550 °C), and then it rapidly reacts to give Bi4Ti3O12. No trace of the peritectic reaction is found in the case of the activated mixture. The complete formation of Bi4Ti3O12 can be obtained by 3-h annealing of the activated mixture at T ≥ 650 °C. The heat capacity of the product phase Bi4Ti3O12 has also been measured in the temperature range 50–300 °C.