High-temperature calorimetric measurements on RE2TeO6 (RE = Gd, Er)

Abstract

The ternary compounds of Gd2TeO6 (s) and Er2TeO6 (s) were prepared by solid-state route and characterized by XRD, ICP-AES and ICP-MS techniques. Enthalpy measurements were taken on these compounds by inverse drop calorimetric method by using a high-temperature differential calorimeter over the temperature region 669–1272 K. The measured enthalpy increment values of these compounds were fitted to four term nonlinear polynomial functions in temperature using least-squares method. With the fitted equations, other thermodynamic function such as heat capacity, entropy and free energy functions have been computed in the temperature range 298–1300 K. The derived free energy functions of RE2TeO6 (RE = Gd, Er), from enthalpy increments measurements were combined with the standard Gibbs energies of formation of RE2TeO6 (RE = Gd, Er), derived from vapor pressure measurement, to obtain $$\Delta _{\text{f}} H_{298}^{\text{o}}$$ of Gd2TeO6 (s) and Er2TeO6 (s).