The phase transitions of ferroelectric Sr2Ta2O7 crystals by MDSC, Brillouin and dielectric spectroscopy

Abstract

The structural phase transitions of Sr2Ta2O7 single crystals have been studied by the modulated temperature differential scanning calorimetry (MDSC), Brillouin scattering and dielectric spectroscopy. The specific heat (Cp) was measured over a wide temperature range from −150°C to 25°C and from 100°C to 210°C. The Cp curve showed an anomaly at To = 166.7°C, indicating the phase transition Cmcm → P21/m. The transition enthalpy ΔH, the transition entropy ΔS and specific heat jump ΔCp at To were estimated to be 0.465 J g−1, 1.01 mJ g−1 K−1 and 9.78 mJ g−1 K−1, respectively. The Cp anomaly associated with the ferroelectric phase transition at Tc = −107°C has not been detected. However, both Brillouin and dielectric data showed the anomalies corresponding to the ferroelectric phase transition from P21/m to P21.