High thermoelectric properties of Cu2Te Ag2Te composite with Fe addition and non-stoichiometric Te

Cu2Te-based materials are a type of superionic conductor belonging to the class of phonon-liquid electron-crystal materials and have achieved high ZT values by doping and nanostructuring. However, it is easy to form copper vacancies in Cu2Te which leads to an excessive carrier concentration and then results in a low Seebeck coefficient. Hence, controlling copper ion migration and optimizing carrier concentration is essential to improve the thermoelectric performance of Cu2Te. This paper reports high-performance Cu2TeAg2Te composite with high application value in the low-middle temperature region, which is achieved by fine tuning the carrier concentration using Fe addition and non-stoichiometric Te, as well as controlling the thermal conductivity of composite. A high ZT of ∼1.2 is obtained in AgCu0.97Fe0.03Te0.96 at a low temperature of 573 K. Meanwhile, the phase transition mechanism of Cu2TeAg2Te and its effect on the thermoelectric transport performance are revealed that go beyond nanostructuring and single-doping, which provides a strong theoretical basis for research and performance improvement of thermoelectric materials in this system.