Ferroelectric phase transitions studied by dielectric and light scattering spectroscopies on Ba1−xCaxTiO3 single crystals (x = 0.12, 0.20)

The ferroelectric phase transition of Ca-substituted barium titanate single crystals, Ba1−xCaxTiO3 (BCTO-x), with x = 0.12 and 0.20 grown by optical floating zone method were studied by dielectric and Brillouin scattering methods. The X-ray diffraction investigation confirmed the structural phase transition from cubic to tetragonal phase in BCTO-x. The dielectric constant exhibited a sharp peak at the ferroelectric phase transition temperature (Tc) and a deviation from the Curie–Weiss law on approaching Tc from the high-temperature side. Brillouin scattering results showed that, similar to the acoustic properties of BCTO-0.20, dynamic precursor polar clusters are formed in the paraelectric phase of BCTO-0.12 single crystals which interact with acoustic waves via electrostrictive coupling resulting in large acoustic anomalies near Tc. However, the temperature dependence of the dielectric constant indicated that diffuseness of the ferroelectric phase transition of BCTO-x became enhanced with Ca content, which was attributed to compositional disorder induced by random substitution of Ba cations by Ca ions.