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).