Thermodynamic Analysis of the HgTe ‐ CdTe ‐ Te System Using the Simplified RAS Model

Abstract

A quantitatively good overall fit is obtained to the phase diagram and thermodynamic data in the system. In the binaries the partial pressures along the three‐phase curves are fit in addition to the liquidus points. Moreover, the liquid phase parameters are constrained so that the enthalpy and entropy of mixing of the stoichiometric binary melts are properly related to the enthalpy and entropy of formation of the binary compounds. Also included in the fit are the pseudobinary liquidus and solidus points, the partial pressure of Hg in the pseudobinary melt, and the partial pressures of Hg, Cd, and for the Te‐saturated pseudobinary solid, . Finally, a choice is made for the most reliable ternary liquidus points and these are included. Portions of the phase diagram, as yet unmeasured, are then calculated and presented. The liquid phase is described by a simple extension of the regular associated solution model of Jordan and Szapiro in which the interaction coefficients and dissociation constants are allowed to depend upon temperature. The partial molar quantities for the liquid phase components are derived and used in liquidus equations that are more exact than the commonly used version of the Vieland equation. Errors in some previous studies are discussed in the appendix. It is concluded that the model cannot provide a satisfactory fit to the entire Hg‐Cd‐Te system. Neither can it fit analogous systems in which the liquidus lines of the binary compounds are asymmetric.