Suppressed phase transition and enhanced thermoelectric performance in iodine-doped AgCuTe

AgCuTe has been recognized as a promising thermoelectric material due to its reported ultralow lattice thermal conductivity, but its phase transition and unsatisfactory thermoelectric performance at close to room temperature restrict its application for the harvesting of low-grade heat. In this work, the near-room-temperature phase transition is successfully avoided by iodine doping at the Te site. In addition, iodine doping effectively reduces the hole concentration, thus greatly increasing the Seebeck coefficient and improving the average power factor, as well as reducing the electronic thermal conductivity. Consequently, a room-temperature ZT of ~0.35 and a maximum ZT of ~0.9 at 463 K were obtained in AgCuTe_0.9I_0.1, leading to a high average ZT of ~0.6 between 303 and 463 K. Our work paves a new way for realizing stable high performance in AgCuTe-based materials for thermoelectric applications.