Influence of Halide Substitution on Local and Average Structure, Lattice Dynamics, and Transport Properties in Cu6PS5X Argyrodites

Halide substitution modifies the Cu + conductivity through changes in the activation energy and the Arrhenius pre-exponential factor, following the Meyer-Neldel behavior, with additional contributions from variations in jump distances and migration pathways. Direction-projected phonon density of states analysis identifies low-frequency Cu + vibrational components along the crystallographic migration pathways. Analysis of the Meyer-Neldel slope further suggests phonon assisted ion hopping involving multi-phonon excitation of low-frequency Cu + vibrational modes.

Together, these findings offer insight into structure-property relationships in Cu 6 PS 5 X and suggest that, alongside the migration energy landscape, the vibrational energy scale, thermal population, and directionality of mobile ion modes should be considered when interpreting ion transport, thereby providing a vibrational perspective for the design of solid-state ion conductors.