Heat capacity at constant pressure and thermodynamic properties of phase transitions in PbMO3 (M=Ti, Zr and Hf)

The heat capacity of PbMO3 (M=Ti, Zr and Hf) at constant pressure was measured using a differential scanning calorimeter (DSC) from room temperature up to 870 K. Large anomalies were found in the heat capacity curves, corresponding to the ferroelectricparaelectric phase transition in PbTiO3 (PT), the antiferroelectric-paraelectric phase transitions in PbZrO3 (PZ) and PbHfO3 (PH). The transition entropies were estimated as 7.3 J K-1 mol(-1) (PT), 9.9 J K-1 mol(-1) (PZ) and 9.3 J K-1 mol(-1) (PH). These values of transition entropies are much larger than that of a typical displacive-type phase transition.