Probing Ionic Diffusion in Superionic Compounds Using Four-Dimensional Quasielastic Neutron Scattering

Ionic mobility plays a central role in a wide range of energy-related technologies, whether in solid-state battery electrodes and electrolytes or as a mechanism for reducing thermal conductivity in thermoelectric compounds. The goal of optimizing the ionic conductivity for such applications requires an understanding of the microscopic diffusion pathways, residence times, activation energies, and the interplay between the mobile ion and the local relaxations of the surrounding lattice. Quasi-elastic neutron scattering (QENS) offers a direct method of probing ionic diffusion, providing diffusion coefficients, average residence times, and hopping lengths using jump diffusion models. Recent advances in single crystal inelastic neutron scattering now allow QENS to be measured in four-dimensional (Q,ω)-space. We will discuss measurements using CNCS at the Spallation Neutron Source of the fluorite compounds, SrCl₂, within the superionic phase at 1050K, in which the Q-dependence of the linewidths of both incoherent and coherent scattering are sensitive to the self-correlation function and local relaxations around the hopping vacancies, respectively.