Gibbs energy of formation of orthorhombic CaZrO₃

Abstract

The Gibbs free energy of formation of the orthorhombic form of CaZrO₃(o) from monoclinic ZrO₂(m) and periclase CaO(p) has been determined as a function of temperature in the range 950–1225 K, using an electrochemical cell incorporating single-crystal CaF₂ as the solid electrolyte. The results are corrected for the small solid solubility of CaO in ZrO₂. For the reaction, ZrO₂(m)+CaO(p)→CaZrO₃(o), ΔG⊖ = −31 590 − 13.9T(± 180) J mol⁻¹. The “second-law” enthalpy of formation of CaZrO3 obtained from the results of this study at a mean temperature of 1090 K is in excellent agreement with the high-temperature solution calorimetric measurements of Muromachi and Navrotsky at 1068 K (J. Solid State Chem., 72 (1988) 244), and the average value of the bomb and acid solution calorimetric studies of Lvova and Feodosev (Zh. Fiz. Khim., 38 (1964) 28), Korneev et al. (Izv. Akad. Nauk SSSR, Neorg. Mater., 7 (1971) 886) and Brown and Bennington (Thermochim. Acta, 106 (1986) 183). The standard entropy of CaZrO₃(o) at 298.15 K from the free energy data is 96.4 (±3.5) J K⁻¹ mol⁻¹. The results of this study are discussed in comparison with high-temperature e.m.f. measurements reported in the literature on cubic zirconia solid solutions.