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

Abstract

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 (T-c) and a deviation from the Curie Weiss law on approaching T-c 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 T-c. 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.