THERMODYNAMIC CHARACTERIZATION OF THE SOLID SOLUTIONS, LEAD(1-X)TIN(X)TELLURIUM, FOR X = 0.0, 0.13, 0.20, AND 1.0
The partial pressures of Te(,2)(g), PbTe(g) and SnTe(g) over the semiconducting solid solutions (Pb(,1-x)Sn(,x))(,1-x)Te(,y)(s) for x-values of 0.0, 0.13, 0.20, and 1.0 were measured for the Te-saturated and for the Pb-Sn-saturated conditions. They were also measured for x-values of 0.13 and 0.20 for known values of y falling within the solid solution homogeneity range. The experimental technique consists of measuring the optical absorbance between 230 and 760 nm of the vapor coexisting with a sample of the solid solution in a sealed optical cell of known volume and temperature. The samples were synthesized by reaction in the sealed cell of weighed amounts of the spectroscopically pure, vacuum melted elements. The measurements on the PbTe and SnTe binary solid solutions were repeated and extended over a wider temperature range. A more complete characterization of the PbTe and SnTe absorption spectra was obtained. These allowed the values of the enthalpy of fusion as well as the Gibbs energy of dissociation for PbTe and SnTe to be redetermined. Enthalpies of fusion of PbTe(s) and SnTe(s) were found to be 11.332 and 10.921 kcal/mole, respectively. These partial pressure data allow the calculation of the partial pressures of Pb(g) and Sn(g) as well as the Gibbs energies of formation of the solid solutions. Following statistical thermodynamic arguments, these quantities are independent of 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, PbTe and SnTe, as is also true for all of the integral molar thermodynamic properties. In particular, the Gibbs-Duhem relation holds between (mu)(,PbTe) and (mu)(,SnTe) and the solid solution is nearly an ideal solution of the binary alloys. The equilibrium solidus and liquidus temperatures of five Te- rich ternary composition were obtained directly from the optical absorbance measurements. The measured values of y - 1/2 along the Te-saturated solidus line for x = 0.13 and 0.20 were compared with the measured Hall constants. Such a comparison comfirms that the vacancies in the metal-sublattice of these solid solutions are doubly-ionized; and gives values of Hall factor, r, as 0.845 for x = 0.13 and as 0.725 for x = 0.20.
"THERMODYNAMIC CHARACTERIZATION OF THE SOLID SOLUTIONS, LEAD(1-X)TIN(X)TELLURIUM, FOR X = 0.0, 0.13, 0.20, AND 1.0"
(January 1, 1986).
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