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. How- ever, the formation of Bi4Ti3O12 is not complete at temper- atures 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 mix- ture. The complete formation of Bi4Ti3O12 can be obtained by 3-h annealing of the activated mixture at T C 650 °C. The heat capacity of the product phase Bi4Ti3O12 has also been measured in the temperature range 50–300 °C.