Tl–Bi–Er–Te System in the Composition Region Tl2Te–Tl9BiTe6–Tl9ErTe6

Abstract

Phase equilibria in the quaternary system Tl–Bi–Er–Te in the composition region Tl₂Te–Tl₉BiTe₆–Tl₉ErTe₆ were studied by physicochemical analysis methods. The phase diagram of the boundary system Tl₂Te–Tl₉BiTe₆ was refined. It was shown that this system is a quasi-binary system of the peritectic type and is characterized by the formation of limited solid solutions based on the initial compounds. A number of diagrams were constructed for the first time, namely, some polythermal sections; the isothermal sections of the phase diagram at 300, 760, and 780 K; and the projections of the liquidus and solidus surfaces of the system Tl₂Te–Tl₉BiTe₆–Tl₉ErTe₆. It was demonstrated that, in this system, there is a wide region of solid solutions with the Tl₅Te₃ structure (δ-phase), which occupies more than 90% of the area of the concentration triangle. The homogeneity range of Tl₂Te is 5–7 mol %. The obtained results can be used for choosing the compositions of solution melts and the temperature conditions for growing crystals of the δ-phase of a given composition, which are of practical interest as promising thermoelectric and magnetic materials.