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 car ried out at temperatures between room temperature and 1180 K by the drop me thod using a high-temperature Calvet micro-calorimeter. The enthalpy increm ent values were given for CaTiO3 and (Ca0.80Pu0.20)TiO3 in polynomial expre ssions of temperature using Shomate's method. Heat capacity equations obtai ned in this study were used to derive the thermodynamic functions, namely e ntropy and free energy function, and to determine the thermodynamic formati on values, namely the standard molar enthalpy of formation, the standard mo lar Gibbs free energy of formation and the standard molar entropy of format ion. The Gibbs free energy of formation of (Ca0.80Pu0.20)TiO3 was smaller t han that of CaTiO3 in the temperature range from room temperature to 1200 K , showing that (Ca0.80Pu0.20)TiO3 is thermodynamically more stable than CaT iO3. The thermodynamic stability of CaTiO3 uas found to increase by means o f Pu substitution for Ca in CaTiO3. (C) 2001 Elsevier Science B.V. All righ ts reserved.