1. Extreme phonon anharmonicity underpins superionic diffusion and ultralow thermal conductivity in argyrodite Ag8SnSe6
- Author
-
Ren, Qingyong, Gupta, Mayanak K., Jin, Min, Ding, Jingxuan, Wu, Jiangtao, Chen, Zhiwei, Lin, Siqi, Fabelo, Oscar, Rodríguez-Velamazán, Jose Alberto, Kofu, Maiko, Nakajima, Kenji, Wolf, Marcell, Zhu, Fengfeng, Wang, Jianli, Cheng, Zhenxiang, Wang, Guohua, Tong, Xin, Pei, Yanzhong, Delaire, Olivier, and Ma, Jie
- Abstract
Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite Ag8SnSe6using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed ‘liquid-like thermal conduction’ picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity (<0.5 W m−1K−1) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.
- Published
- 2023
- Full Text
- View/download PDF