Thermodynamic stability of Sm2TeO6

The vapour pressure of Sm2TeO6 was measured using a thermal analyser with a horizontal arm. This TG based transpiration technique, was validated by measuring the vapour pressure of pure TeO2(s). The temperature dependence of the latter was measured to be log p (Pa) = {14.2 − 13321/T (K)} (±0.03) in the range 884–987 K. These data yielded a ΔH298°ΔH298° value of 269.7 ± 0.6 kJ mol−1 for the enthalpy of sublimation (third-law method) of TeO2 which compared well with the data reported in the literature. The temperature dependence of the vapour pressure of TeO2 over the mixture Sm2TeO6(s) + Sm2O3(s) generated by the incongruent vapourisation reaction,Sm2TeO6(s) → Sm2O3(s) + TeO2(g) + 1/2O2(g)could be expressed aslog p (Pa)={18.56−25469/T (K)}±0.06 (1374−1533 K)log p (Pa)={18.56−25469/T (K)}±0.06 (1374−1533 K)The standard Gibbs energy of formation of Sm2TeO6(s) was derived from the above vapour pressure data in conjunction with auxiliary data for the other coexisting phases. The temperature dependence of the Gibbs energy of formation of Sm2TeO6 over the temperature range 1374–1533 K could be represented asΔGf°(Sm2TeO6)(kJ mol−1)={−2399.3+0.5714 T (K)}±5.8ΔGf°(Sm2TeO6)(kJ mol−1)={−2399.3+0.5714 T (K)}±5.8The Gibbs energy of formation of Sm2TeO6(s) is being reported for the first time.