Thermodynamic properties of ternary barium oxides

Abstract

The vapor pressure over the two-phase mixture of CeO 2 + BaCeO 3 has been measured by mass spectrometry in the temperature range 1774–1947 K. BaO(g) only was identified as being the main gas species. From the vapor pressure of BaO(g) over CeO 2 + BaCeO 3, the standard molar enthalpy of formation of BaCeO 3 has been determined by second and third law treatments and is compared with those values calculated by the use of Aronson's semiempirical equation in this study and obtained previously by solution calorimetry. The standard molar Gibbs energies of formation of BaCeO 3, BaZrO 3 and Ba 2ZrO 4 have also been determined as a function of temperature from the respective vapor pressures of BaO(g) over CeO 2 + BaCeO 3 in this study and those over ZrO 2 + BaZrO 3 and BaZrO 3 + Ba 2ZrO 4 previously determined by the present author and co-workers. The experimental values of the standard molar Gibbs energy of formation and the standard molar enthalpy of formation of other ternary barium oxides such as BaMoO 3, BaMoO 4, BaUO 3, BaUO 4, BaTiO 3, Ba 2TiO 4, BaThO 3 and BaPuO 3 are summarized and the latter is compared with calculated values from Aronson's equation. The relative stability of barium perovskite oxides is briefly discussed from the Goldschmidt tolerance factors and the molar enthalpies of formation of the perovskite oxides from the constituent binary oxides.