Si–Te System: Partial Pressures of Te2 and SiTe and Thermodynamic Properties from Optical Density of the Vapor Phase

The optical density between 2400 and 7000 Å of the vapor in equilibrium with Si–Te samples containing between 10 and 100 at.% Te was measured for sample temperatures between 500° and 940°C. The partial pressures of Te₂(g), $p_{{\mathrm{Te}}_2}$ , were obtained from the optical densities at 4357, 5000, and/or 5500 Å, where SiTe(g) does not absorb. A plot of $p_{{\mathrm{Te}}_2}$ vs ${10}^3\mathrm{\hspace{0.17em}/\hspace{0.17em}T}$ shows the existence of a single compound, Si₂Te₃(c), whose homogeneity range falls within outer limits of 59.45 and 60.50 at.% Te and ends at a peritectic temperature of 892°C. X‐ray powder diffraction patterns indicate the Si₂Te₃(c) phase is the same as that previously identified by some authors as SiTe₂(c). The net SiTe(g) optical densities at 2708 and 2893 Å were determined and found to be in constant ratio to one another. For 0.4 Si(c) + 0.6 Te(1)→Si_0.4Te_0.6(c), the standard Gibbs free‐energy change is ${\mathrm{\Delta G}}_f{\text{°\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}5.754\hspace{0.17em}+\hspace{0.17em}3.904(10}}^{\text{−3}}\mathrm{)T}\mathrm{kcal}\mathrm{\hspace{0.17em}/\hspace{0.17em}}\mathrm{g‐atom}$ between 604° and 892°C. For the reaction $\mathrm{Si}(\mathrm{g}\mathrm{)\hspace{0.17em}+\hspace{0.17em}}\frac{1}{2}{\mathrm{Te}}_2(\mathrm{g}\mathrm{)\hspace{0.17em}\to \hspace{0.17em}}\mathrm{SiTe}(\mathrm{g})$ , it is ${\mathrm{\Delta G}}_f{\text{°\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}74.86\hspace{0.17em}+\hspace{0.17em}15.77(10}}^{\text{−3}}\mathrm{)T}\mathrm{kcal}\mathrm{\hspace{0.17em}/\hspace{0.17em}}\mathrm{mole}$ (700°–892°C).