Ferroelectric transition of Aurivillius compounds Bi5Ti3FeO15 and Bi6Ti3Fe2O18

Single-phase Bi5Ti3FeO15 and Bi6Ti3Fe2O18 ceramics have been synthesized by solid state reaction. The ferroelectric transition of the compounds was studied by differential scanning calorimetry, high-temperature x-ray diffraction, and temperature-dependent dielectric measurements. Two solid-state structural transitions were observed in both compounds, one is the orthorhombic↔tetragonal transition (ferroelectric transition) at 1021 K for Bi5Ti3FeO15 and 973 K for Bi6Ti3Fe2O18, and the other is accompanied by an abrupt lattice expansion of the tetragonal phase at about 1110 K for Bi5Ti3FeO15 and about 1090 K for Bi6Ti3Fe2O18.