Homogeneity Ranges of Tl5Te2Cl and Tl5Te2Br

This paper systematizes phase-diagram data or the Tl-TlCl(Br)-Te systems and presents their 500-K subsolidus phase diagrams. Tl5Te2Cl and Tl5Te2Br (Tl5Te3 structure) are shown to be nonstoichiometric compounds with wide homogeneity ranges, which have been accurately determined using emf measurements, x-ray diffraction, and microhardness tests. Using emf data for reversible concentration cells with a thallium electrode, we have evaluated the partial thermodynamic functions of the thallium in the alloys studied, the standard thermodynamic functions of formation of Tl5Te2Cl and Tl5Te2Br, and their standard entropies. The crystal chemistry of these phases of variable composition is discussed in relation to the Tl5Te3 structure.