Synthesis, phase transformation and dielectric properties of sol–gel derived Bi2Ti2O7 ceramics

Sol–gel derived Bi2Ti2O7 ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi2Ti2O7 phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi4Ti3O12 and Bi2Ti4O11 at 850–1150 °C. The single phase of Bi2Ti2O7 reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm−2 and coercive field is 24 kV cm−1. Thus, the Bi2Ti2O7 did not exhibit ferroelectricity, but the mixed phase of Bi4Ti3O12 and Bi2Ti4O11 did.