THERMODYNAMIC PROPERTIES OF HGTE-CDTE SOLID-SOLUTIONS

Partial pressures of Hg between about 10(-8) and 10(-5) atm over Te-saturated solid solutions of HgTe and CdTe have been determined between 400-500 K for 0, 9.4, 19.6, 39.0, and 54.0 mole% CdTe by measuring the optical density of the coexisting vapor at 253.7 nm. A third law analysis of the Gibbs energy of formation obtained for HgTe(c), which includes published high temperature data, gives DELTAH(f,298)0 = - 43.69 +/- 0.28 kJ/mole and DELTAS(f,298)0 = - 20.51 +/- 0.49 J/mole-K. In agreement with published emf measurements a miscibility gap occurs. The 9.4 and 19.6 mole% CdTe solid solutions are outside the gap above about 406 K; the 39% solid solution leaves the gap at about 427 K. X-ray diffraction lines show increasing broadening with time, consistent with the formation of a gap. The present data and that from the low temperature emf measurements are combined with published high temperature partial pressure measurements to construct an equation for the thermodynamics of mixing of the solid solutions.