Thermodynamic properties of BaTeO 3(s)

Abstract

The standard molar Gibbs energy of formation of barium tellurite, BaTeO 3(s), was determined by the transpiration technique using pure oxygen as the carrier gas in the temperature range 1133 K to 1260 K. The condensate was exclusively identified as TeO 2(s) by chemical analysis. From a quantitative chemical analysis of the condensed TeO 2(s), the vapour pressure of TeO 2(g) over pure BaTeO 3(s) was calculated and is given by ln{ p(TeO 2, g) /kPa ±0.1} = 18.64 − 30863.2 · (K/T). The Gibbs energy of formation of BaTeO 3(s) was computed from the values of ln{ p(TeO 2, g) /kPa} and the values of ΔfGmofor BaO(s) and TeO 2(g) taken from the literature and is given by { ΔfGmo(BaTeO 3, s, T) /kJ · mol −1± 1.0} =−856.5 + 0.2067 · (T/K).The enthalpy increments of BaTeO 3(s) were measured using a high-temperature Calvet micro-calorimeter in the temperature range 304 K to 1000 K. Enthalpy increment values are represented by a polynomial of the form { Ho(T)−Ho(298.15 K)}/(J · mol−1) =−39 190+118.96·(T/K)+4.235·10−3·(T/K)2+9.975·105·(K/T), with an accuracy of ±0.4 per cent over the interval (304 ⩽T/K⩽ 1000).