The Equilibrium Partial Pressure of HgI 2 over and Thermodynamic Properties of Hg 3 Te 2 I 2 1)

The high temperature vaporization pattern of Hg 3 Te 2 I 2 (s,l) shows four distinctly different regimes, similar to those of the HgTe vaporization. The most predominant species in the vapor phase in all four regimes is HgI 2 (g), followed by Hg(g) and, possibly, Te 2 I 2 (g). The width of the “homogeneity range” of Hg 3 Te 2 I 2 (s) was determined to be less than about 0.17 mole‐% HgI 2 . Applying the second‐law method to the vaporization of HgTe‐saturated Hg 3 Te 2 I 2 (s) at higher temperatures yields the heat and entropy of vaporization of 20.9 ± 2.3 (kcal/mole) and of 27.5 ± 2.8 (cal/mole K), respectively, with estimated total uncertainties of less than ± 5.8 (kcal/mole) and ± 7.6 (cal/mole K), at an average temperature of 722 K. With an estimated heat capacity function of Hg 3 Te 2 I 2 (s) and estimated thermodynamic values for HgI 2 ‐saturated HgTe(s), the heat of formation and absolute entropy of Hg 3 Te 2 I 2 (s) are computed to be ${\rm \Delta}{\rm H}{\rm ^{o}_{298}}_{f}$ = −49.7 ± 1.1 (kcal/mole) and ${\rm \Delta}{\rm H}{\rm ^{o}_{298}}$ = 97.3 ± 1.4 (cal/mole K), with estimated total uncertainties of ± 8.3 (kcal/mole) and ± 14.0 (cal/mole K). The combined results of this investigation provide valuable information for the crystal growth of this material from the vapor and molten phase.