Tellurium Oxides: Thermodynamics and Phase Relations in the Te–O System

Abstract

The Te–O phase diagram and the TeO₂ thermodynamic properties are of interest for many industrial fields: nuclear applications, steel making industry and chalcogenide glass processes. Both, the thermodynamic properties and phase diagram of this relevant binary system were reviewed and assessed using the Calphad method. From this assessment, the standard Gibbs free energy and corresponding heat capacity of the binary oxides are calculated as:

$$\begin{gathered} \Delta_{{\text{f}}} {\text{G}}_{{{\text{TeO}}_{2} }}^{ \circ } \left( {{\text{KJ}} \cdot {\text{mol}}^{ - 1} } \right) = - 109.646 + 0.1034 \cdot T - 0.0064 \cdot T \cdot \ln (T) \hfill \\ {\text{C}}_{{{\text{p}}_{{{\text{TeO}}_{2} }} }} \left( {{\text{J}} \cdot {\text{K}} \cdot {\text{mol}}^{ - 1} } \right) = 19.59 + 0.0101 \cdot {\text{T}} - 1.6 \cdot 10 ^{- 6}.T^{2} - 186517 \cdot T^{ - 2} \hfill \\ \end{gathered}$$

$$\begin{gathered} \Delta_{{\text{f}}} {\text{G}}_{{{\text{Te}}_{2} {\text{O}}_{5} }}^{ \circ } \left( {{\text{KJ}} \cdot {\text{mol}}^{ - 1} } \right) = - 104.81 + 0.1175 \cdot T - 0.0077 \cdot T \cdot \ln (T) \hfill \\ {\text{C}}_{{{\text{p}}_{{{\text{Te}}_{2} {\text{O}}_{5} }} }} \left( {{\text{J}} \cdot {\text{K}}^{ - 1} \cdot {\text{mol}}^{ - 1} } \right) = 19.86 + 0.0091 \cdot T - 285181 \cdot T^{ - 2} \hfill \\ \end{gathered}$$

$$\begin{gathered} \Delta_{{\text{f}}} {\text{G}}_{{{\text{TeO}}_{3} }}^{ \circ } \left( {{\text{KJ}} \cdot {\text{mol}}^{ - 1} } \right) = - 92.79 + 0.111 \cdot T - 0.00776 \cdot T \cdot \ln (T) \hfill \\ {\text{C}}_{{{\text{PTeO}}_{3} }} \left( {{\text{J}} \cdot {\text{K}}^{ - 1} \cdot {\text{mol}}^{ - 1} } \right) = 17.475 + 0.013 \cdot {\text{T}} - 2.085 \cdot 10^{ - 6} \cdot T^{2} - 280000 \cdot T^{ - 2} \hfill \\ \end{gathered}$$