FURTHER THERMODYNAMIC CHARACTERIZATION OF THE MERCURY-CADMIUM - TELLURIUM SYSTEM BY OPTICAL ABSORBANCE OF THE VAPOR PHASE (LIQUIDUS TEMPERATURE, TIE-LINE DATA, GIBBS FREE ENERGIES OF FORMATION)
The previously developed optical absorbance technique was utilized to extend the study of the thermodynamic properties and the phase equilibria in the mercury-cadmium-tellurium system. The equilibrium partial pressures of mercury, cadmium, and tellurium over (Hg(,1-x)Cd(,x))(,y)Te(,1-y) in the temperature range 300-860(DEGREES)C were determined by measuring the optical absorbance of the coexisting vapor between 200 and 850 nm. The quantitative correlations between the characteristic absorption of Hg(g), Cd(g), and Te(,2)(g) and their vapor pressures were repeated and extended to higher optical cell temperatures. These calibration results enable the extension of the partial pressure measurements over a wider temperature range than before. The Hg-Cd amalgams were studied more closely and the foreign gas broadening parameters for both 228.7 and 325.7 nm Cd lines under the influence of relatively high Hg pressures were redetermined. The partial pressures of Hg, Cd, and Te(,2) for Te-saturated, x = 0.196 and 0.39 in the formula Hg(,1-x)Cd(,x)Te(s) were repeated and extended over a wider temperature range. Those for x = 0.70 and 0.95 were also determined. The pressure ranges covered are 10('-2)-15 atm for Hg, 10('-8)-10('-4) atm for Cd, and 10('-5)-10('-2) atm for Te(,2), and Hg is always the predominant vapor species. The chemical potentials of HgTe and CdTe as well as the Gibbs free energies of formation of the solid solution for these compositions were calculated from the partial pressure data. Consistent with the statistical thermodynamic arguements, these free energies are independent of the Te-to-metal ratio within the experimental error and the solid solution can be described as effectively being a binary solution containing two thermodynamic components, HgTe and CdTe. In particular, the Gibbs-Duhem relation holds between (mu)(,HgTe) and (mu)(,CdTe) at least qualitatively and the solid solution is nearly an ideal solution of the binary alloy. The equilibrium liquidus temperatures of four Te-rich ternary liquid composition were obtained directly from the optical absorbance measurements and the tie-lines were established by comparing the partial pressures of Hg measured for the liquid at their liquidus temperatures with those of the pseudobinary solid solutions at the same temperature. The results agree fairly well with those obtained by the modified direct observation technique.
"FURTHER THERMODYNAMIC CHARACTERIZATION OF THE MERCURY-CADMIUM - TELLURIUM SYSTEM BY OPTICAL ABSORBANCE OF THE VAPOR PHASE (LIQUIDUS TEMPERATURE, TIE-LINE DATA, GIBBS FREE ENERGIES OF FORMATION)"
(January 1, 1983).
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