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

Abstract

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.