Measurement and Assessment of the Thermodynamic Properties and the Phase Diagram of the Cd–Te System

Abstract

The enthalpy of formation of the CdTe compound was determined from its heat of solution at 773 K using a twin solution calorimeter. The heat contents of binary Cd–Te compositions were measured by a drop calorimeter in the concentration range from XTe=0.50 to 0.95 and in the temperature range from 800 to 1500 K. A method of thermodynamic analysis was applied to the obtained data to derive the other thermodynamic properties. For the first time enthalpies of mixing of the liquid Cd–Te system are derived from the experimental data. The enthalpy and entropy of mixing of the liquid Cd–Te phase show large negative values in the neighborhood of the compound composition. These strongly temperature dependent anomalies are explained by a chemical short range order in liquid alloys. The obtained thermodynamic and phase diagram data for the Cd–Te system were used to reassess the system following CALPHAD standard. An associated solution model for the liquid phase and standard Gibbs energy functions for the three solid phases (Cd, CdTe and Te) were used. The phase diagram and thermodynamic properties calculated from the reassessed system agree well with the experimental data.