Thermodynamic stability of Sm 2TeO 6

Abstract

The vapour pressure of Sm 2TeO 6 was measured using a thermal analyser with a horizontal arm. This TG based transpiration technique, was validated by measuring the vapour pressure of pure TeO 2(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 Δ H 298 ° value of 269.7 ± 0.6 kJ mol −1 for the enthalpy of sublimation (third-law method) of TeO 2 which compared well with the data reported in the literature. The temperature dependence of the vapour pressure of TeO 2 over the mixture Sm 2TeO 6(s) + Sm 2O 3(s) generated by the incongruent vapourisation reaction, Sm 2TeO 6(s) → Sm 2O 3(s) + TeO 2(g) + 1/2O 2(g) could be expressed as log p ( Pa ) = { 18.56 − 25469 / T ( K ) } ± 0.06 ( 1374 − 1533 K ) The standard Gibbs energy of formation of Sm 2TeO 6(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 Sm 2TeO 6 over the temperature range 1374–1533 K could be represented as Δ G f ° ( S m 2 Te O 6 ) ( kJ mo l − 1 ) = { − 2399.3 + 0.5714 T ( K ) } ± 5.8 The Gibbs energy of formation of Sm 2TeO 6(s) is being reported for the first time.