# THERMODYNAMIC PROPERTIES AND PHASE DIAGRAM CALCULATION OF THE MERCURY-CADMIUM - TELLURIUM SYSTEM

#### Abstract

The partial pressures of Hg, Cd and Te(,2) are determined for the solid solution, (Hg(,1-x)Cd(,x))(,y)Te(,1-y)(s), for x-values of 0.1, 0.2 and 0.58 by measuring the optical absorbance of the coexisting vapor between 220 and 800 nm. The pressure ranges covered are 10('-2)-32 atm for Hg, 10('-8)-10('-5) atm for Cd, and 10('-5)-10('-2) atm for Te(,2), and Hg is always the predominant vapor species. The solidus temperatures are obtained directly from the optical absorbance measurements. The chemical potentials of HgTe and CdTe and the Gibbs energies of formation for the solid solutions are derived from these pressures. These chemical potentials, (mu)(,HgTe) and (mu)(,CdTe), are found to be independent of y and a function of temperature T, and x as expected theoretically. The experimental data obey the Gibbs-Duhem relation at least qualitatively in that (mu)(,HgTe) increases at a given T with decreasing x while (mu)(,CdTe) increases with increasing x. The solid solution, within the uncertainty limits, is close to ideal with an entropy of mixing corresponding to the random mixing of Hg and Cd. The extensive phase diagram and thermodynamic data for the Hg-Cd-Te system are critically reviewed and simultaneously and quantitatively fit within a thermodynamically self-consistent framework. The liquid phase is modeled as an associated solution in which the interactions of the species are given by quadratic and cubic terms in the species mole fractions with linearly temperature dependent coefficients. The associated species are taken as CdTe and HgTe. The solid solution phase is characterized by assuming that its thermodynamic components, HgTe and CdTe, mix like a quasiregular solution. The simultaneous fit to the diverse data is generally within plausible estimates of the uncertainties in the experimental data. A reliable means of smoothing and evaluating the experimental data and of guiding further experiments is thus obtained.

#### Recommended Citation

TUNG, TSE, "THERMODYNAMIC PROPERTIES AND PHASE DIAGRAM CALCULATION OF THE MERCURY-CADMIUM - TELLURIUM SYSTEM" (1983). *Dissertations (1962 - 2010) Access via Proquest Digital Dissertations*. AAI8409287.

https://epublications.marquette.edu/dissertations/AAI8409287