Cao, Ruyue; Yan, Lei; Yang, Kaike; Cai, Xuefen; Jia, Tiantian; Luo, Jun-Wei; Li, Shu-Shen; Wei, Su-Huai; Robertson, John; Deng, Hui-Xiong Source: Journal of Physical Chemistry Letters, p 7055-7060, 2024; E-ISSN: 19487185; DOI: 10.1021/acs.jpclett.4c00955; Publisher: American Chemical Society

Articles not published yet, but available online Article in Press

Author affiliation:

State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing; 100083, China

Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing; 100049, China

Department of Engineering, University of Cambridge, Cambridge; CB2 1PZ, United Kingdom

Science and Technology on Low-Light-Level Night Vision Laboratory, Xi’an; 710065, China

Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, Key Laboratory for Matter Microstructure and Function of Hunan Province, Synergetic Innovation Center for Quantum Effects and Applications, Department of Physics, Hunan Normal University, Changsha; 410081, China

Beijing Computational Science Research Center, Beijing; 100193, China

Abstract:

The low thermal conductivity of group IV-VI semiconductors is often attributed to the soft phonons and giant anharmonicity observed in these materials. However, there is still no broad consensus on the fundamental origin of this giant anharmonic effect. Utilizing first-principles calculations and group symmetry analysis, we find that the cation lone-pairs s electrons in IV-VI materials cause a significant coupling between occupied cation s orbitals and unoccupied cation p orbitals due to the symmetry reduction when atoms vibrate away from their equilibrium positions under heating. This leads to an electronic energy gain, consequently flattening the potential energy surface and causing soft phonons and strong anharmonic effects. Our findings provide an intrinsic understanding of the low thermal conductivity in IV-VI compounds by connecting the anharmonicity with the dynamical electronic structures, and can also be extended to a large family of hybrid systems with lone-pair electrons, for promising thermoelectric applications and predictive designs.