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

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) + O-2 (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 O-2 (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.