High‐Performance Thermoelectric α‐Ag9Ga1−xTe6 Compounds with Ultralow Lattice Thermal Conductivity Originating from Ag9Te2 Motifs

摘要

Abstract We have determined the complex atomic structure of high‐temperature α‐Ag9GaTe6 phase with a hexagonal lattice (P63mc space group, a=b=8.2766??, c=13.4349??). The structure has outer GaTe45? tetrahedrons and inner Ag9Te25+ clusters. All of the Ag ions are disorderly distributed in the lattice. Seven types of the Ag atoms constitute the cage‐like Ag9Te25+ clusters. The highly disordered Ag ions vibrate in‐harmonically, producing strong coupling between low frequency optical phonons and acoustic phonons. This in conjunction with a low sound velocity of 1354?m?s?1 leads to an ultralow thermal conductivity of 0.20?W?m?1?K?1 at 673?K. Meanwhile, the deficiency of Ga in Ag9Ga1?xTe6 compounds effectively optimizes the electronic transport properties. Ag9Ga0.91Te6 attains a highest power factor of 0.40?mW?m?1?K?2 at 673?K. All these contribute to a much‐improved ZT value of 1.13 at 623?K for Ag9Ga0.95Te6, which is 41? higher than that of the pristine Ag9GaTe6 sample.