Ferroelectric transition of Aurivillius compounds Bi5Ti3FeO15 and Bi6Ti3Fe2O18

Single-phase ${\text{Bi}}_5{\text{Ti}}_3{\text{FeO}}_{15}$ and ${\text{Bi}}_6{\text{Ti}}_3{\text{Fe}}_2{\text{O}}_{18}$ 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 $\text{orthorhombic}\leftrightarrow \text{tetragonal}$ transition (ferroelectric transition) at 1021 K for ${\text{Bi}}_5{\text{Ti}}_3{\text{FeO}}_{15}$ and 973 K for ${\text{Bi}}_6{\text{Ti}}_3{\text{Fe}}_2{\text{O}}_{18}$ , and the other is accompanied by an abrupt lattice expansion of the tetragonal phase at about 1110 K for ${\text{Bi}}_5{\text{Ti}}_3{\text{FeO}}_{15}$ and about 1090 K for ${\text{Bi}}_6{\text{Ti}}_3{\text{Fe}}_2{\text{O}}_{18}$ .