Structural, Thermal, and Physical Properties of the Thallium Zirconium Telluride Tl2ZrTe3

We have synthesized Tl2ZrTe3 at elevated temperatures starting from the elements. Tl2ZrTe3 adopts a cubic structure, space group P213 with a unit cell parameter of a = 19.118(1) Å (Z = 36). All Tl and Zr atoms are octahedrally (distorted) coordinated by Te atoms. One out of 11 crystallographically distinct Te atoms in the structure is not connected to any Zr atoms, but is surrounded by six Tl atoms in the form of a severely distorted octahedron. Because of the absence of any significant homonuclear interactions, all atoms are in their most common oxidation states, namely, Tl+, Zr4+, and Te2–. Electronic structure calculations and physical property measurements reveal the semiconducting characteristics of the compound. The structure and thermoelectric properties of Tl2ZrTe3 and Tl2SnTe3 are compared in the present work. The dimensionless figure of merit, ZT, was found to be 0.18 for Tl2ZrTe3 at 420 K and 0.31 for Tl2SnTe3 at 500 K, with both materials exhibiting very low thermal conductivity. Tl2ZrTe3 decomposes irreversibly around 450 K in open systems under inert gas atmosphere, while it remains stable up to its incongruent melting point at 835 K in closed silica tubes.