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

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 -150degreesC to 25degreesC and from 100degreesC to 210degreesC. The C-p curve showed an anomaly at T-o 166.7degreesC, indicating the phase transition Cmcm --> P2(1)/ m. The transition enthalpy DeltaH, the transition entropy AS and specific heat jump DeltaC(p) at T-o 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 C-p anomaly associated with the ferroelectric phase transition at T-c = -107degreesC has not been detected. However, both Brillouin and dielectric data showed the anomalies corresponding to the ferroelectric phase transition from P2(1)/m to P2(1).