Enthalpy and heat capacity of (Ca1−xPux)TiO3 (x=0 and 0.20)

Enthalpy increment measurements on (Ca1−xPux)TiO3 (x=0 and 0.20) were carried out at temperatures between room temperature and 1180 K by the drop method using a high-temperature Calvet micro-calorimeter. The enthalpy increment values were given for CaTiO3 and (Ca0.80Pu0.20)TiO3 in polynomial expressions of temperature using Shomateʹs method. Heat capacity equations obtained in this study were used to derive the thermodynamic functions, namely entropy and free energy function, and to determine the thermodynamic formation values, namely the standard molar enthalpy of formation, the standard molar Gibbs free energy of formation and the standard molar entropy of formation. The Gibbs free energy of formation of (Ca0.80Pu0.20)TiO3 was smaller than that of CaTiO3 in the temperature range from room temperature to 1200 K, showing that (Ca0.80Pu0.20)TiO3 is thermodynamically more stable than CaTiO3. The thermodynamic stability of CaTiO3 was found to increase by means of Pu substitution for Ca in CaTiO3.