Partial Pressures and High-Temperature Thermodynamic Properties for the Germanium-Tellurium System

Our earlier optical density measurements over Ge-Te compositions are reanalyzed. Spectral characteristics of the GeTe(g) spectrum are determined from measurements with a 1 at.% Te sample near 1200 K. Beers law constants for GeTe(g) are established by requiring consistency between spectroscopic results for the dissociation of GeTe(g) into Ge(g) and Te2(g) and our description in terms of the partial pressure of Te2 and the partial optical density of GeTe over Ge saturated GeTe(c). Between 870 and 997 K the partial pressures over Ge saturated GeTe(c) are ln P(Te2,atm) = − 24,800/T + 17.600 and ln P(GeTe,atm) = − 23,900/T + 19.400. The latter pressure is about 2.5 times lower than our earlier result. Between 869 and 997 K the Gibbs energy of dissociation of GeTe(g) to Ge(g) and Te2(g) is $$\Delta {\text{G}}_{\text{D}}^{\rm o} = 281{,}254 - 53.59{\text{T}}$$ J/mol while the Gibbs energy of formation of Ge saturated GeTe(c) from Ge(c) and Te(l) is $$\Delta {\text{G}}_{\rm f}^{\rm o} = - \,44{,}994 + 26.978{\text{T}}$$ J/mol. The partial pressures along and within the three phase curve of GeTe(c) and along the three phase curve for Ge(c) are determined and discussed. Comparisons with other types of data are made.