Thermoelectric Properties of TlCu3Te2 and TlCu2Te2

We performed thermoelectric characterizations on TlCu3Te2: (Tl1+)(Cu1+)3 (Te2−)2 and TlCu2Te2: (Tl1+)(Tl3+)(Cu1+)4(Te2−)4, in order to understand the relationship between the thermoelectric properties (especially the lattice thermal conductivity κlat) and the valence states of Tl. The thermal conductivity of TlCu2Te2 is high (about 8 W m−1 K−1), while that of TlCu3Te2 is extremely low (around 0.5 W m−1 K−1) like other thallium tellurides. This high κ of TlCu2Te2 was caused not only by its large electronic contribution but also by its intrinsically high κlat. The present study implies that the valence states of Tl would play some important roles in determining the magnitude of κlat.