Anharmonic host-lattice dynamics enable fast ion conduction in superionic AgI
Thomas M. Brenner, Christian Gehrmann, Roman Korobko, Tsachi Livneh, David A. Egger, Omer Yaffe
Abstract
Solid-state ion conductors simultaneously display crystalline and fluidlike properties. This limits physical understanding of the fundamental mechanism of ion conduction. By analyzing THz-frequency Raman polarization-orientation measurements and \textit{ab initio} molecular dynamics computations, the authors devise a dynamic structural model that captures the simultaneous crystalline and fluid-like properties of the archetypal ion conductor $\ensuremath{\alpha}$-AgI. The analysis demonstrates clear signatures of strongly anharmonic, relaxational motions in the I${}^{\ensuremath{-}}$ host lattice, and that these motions are coupled to mobile ion (Ag${}^{+}$) motion and diffusion.