Low-thermal-conductivity group 13 chalcogenides as high-efficiency thermoelectric materials

Thermoelectric (TE) generators can directly generate electrical power from waste heat and are promising for use in power supplies and for realizing sustainable energy management. However, the low efficiencies of TE materials in converting heat to electricity is the main impediment to applying TE generators in many industries including exhaust heat recovery in automobiles. The efficiency of TE materials is quantified by a dimensionless figure of merit ZT. To enhance ZT, it is important to reduce the lattice thermal conductivity (?lat) of a material while maintaining a high electrical conductivity. Here, we review the TE properties of thallium-based compounds, mainly tellurides. Many thallium tellurides exhibit extremely low ?lat below 0.5?W?m-1?K-1, which is almost one third that of Bi2Te3 used in current TE devices. Of the thallium tellurides, Ag9TlTe5 has the highest ZT value of 1.2, which is higher than typical ZT values 0.8 of Bi2Te3; this is primarily due to the extremely low ?lat of Ag9TlTe5. In addition, we briefly review the TE properties of tellurides of other group 13 elements that contain structural vacancies such as Ga2Te3. Tellurides exhibit various vacancy distributions and hence have interesting TE properties. Based on the results of the TE properties of these tellurides, we propose a strategy for improving TE materials.