Thermodynamic investigations on M₂TeO₆ (s) and M₆TeO₁₂ (s) (M = Gd, Er)

Abstract

The standard Gibbs energies of formation of M₂TeO₆ (s) and M₆TeO₁₂ (s) (where M = Gd, Er) were obtained from vapour pressure measurements by employing thermogravimetry-based transpiration technique. The vapour pressures of TeO₂ (g) over the mixtures M₂TeO₆ (s) + M₆TeO₁₂ (s) (where M = Gd, Er), generated by the incongruent vapourisation reaction, 3 M₂TeO₆ (s) → M₆TeO₁₂ (s) + 2 TeO₂ (g) + O₂ (g) were measured in the temperature range 1,373–1,483 K and 1,293–1,453 K to obtain Gibbs energies of formation of Gd₂TeO₆ (s) and Er₂TeO₆ (s), respectively. Similarly, the vapour pressures of TeO₂ (g) over the mixtures M₆TeO₁₂ (s) + M₂O₃ (s) (where M = Gd, Er), generated by the incongruent vapourisation reaction, M₆TeO₁₂ (s) → 3 M₂O₃ (s) + TeO₂ (g) + 1/2 O₂ (g) were measured in the temperature range 1,673–1,773 K to determine the Gibbs energies of formation of Gd₆TeO₁₂ (s) and Er₆TeO₁₂ (s). From the vapour pressure measurements, the standard Gibbs energies of formation of M₂TeO₆ (s) and M₆TeO₁₂ (s) (where M: Gd, Er) were derived.