Phase range and physical properties of the thallium tin tellurides Tl10−xSnxTe6 (x ≤ 2.2)

Crystal structures and physical property measurements were determined for Tl10−xSnxTe6 with a phase range of 0 ≤ x ≤ 2.2. These tellurides are substitution variants of Tl5Te3. Electronic structure calculations indicate that Tl8Sn2Te6 should be an intrinsic semiconductor, and the Sn-poor variants, extrinsic ones with p-type conduction. The positive Seebeck values increase with increasing Sn content, while the electrical and thermal conductivity values decrease. Low thermal conductivity values, well below 1 W m−1 K−1, are the best asset of these materials with respect to thermoelectric performance. At x = 2.2, the best thermoelectric properties were obtained, with a figure-of-merit ZT = 0.60 at 617 K as determined on sintered cold-pressed pellets.

► Sn may replace up to 22% of Tl in Tl10Te6.
► The higher the Sn content, the better is the thermoelectric performance of Tl10−xSnxTe6.
► The highest figure-of-merit of the sintered cold-pressed pellets is ZT = 0.6 at 617 K
► Further enhancements are expected upon hot-pressing.