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

• Published in: Angewandte Chemie International Edition 2022-09, Vol.61 (36), p.n/a
• Main Authors: Tang, Yingfei, Yu, Yimeng, Zhao, Na, Liu, Keke, Chen, Haijie, Stoumpos, Constantinos C., Shi, Yixuan, Chen, Shuo, Yu, Lingxiao, Wu, Jinsong, Zhang, Qingjie, Su, Xianli, Tang, Xinfeng
• Format: Article
• Language: English
• Subjects: Acoustic velocity; Atomic structure; Clusters; Crystal Structure; Electron transport; Ga Deficiency; Heat transfer; Hexagonal lattice; Ions; Phonons; Power factor; Tetrahedra; Thermal conductivity; Thermoelectrics; Transport properties; Ultralow Lattice Thermal Conductivity; α-Ag9GaTe6
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202208281

We have determined the complex atomic structure of high‐temperature α‐Ag9GaTe6 phase with a hexagonal lattice (P63mc space group, a=b=8.2766 Å, c=13.4349 Å). The structure has outer [GaTe4]5− tetrahedrons and inner [Ag9Te2]5+ clusters. All of the Ag ions are disorderly distributed in the lattice. Seven types of the Ag atoms constitute the cage‐like [Ag9Te2]5+ 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. The high‐temperature crystal structure of α‐Ag9GaTe6 shows a hexagonal structure. Highly disordered Ag atoms vibrate in‐harmonically leading to an intrinsically ultralow lattice thermal conductivity. Meanwhile, the deficiency of Ga in Ag9Ga1−xTe6 compounds effectively optimizes the electronic transport properties. All these factors contribute to an improved thermoelectric Figure of Merit ZT value of 1.13 at 623 K for Ag9Ga0.95Te6.