4D-QENS Analysis of Correlations in Fast-Ion Conductor SrCl2

Methods of elucidating the mechanisms of fast-ion conduction in solid-state materials are pivotal for advancements in energy technologies such as batteries, fuel cells, sensors, and supercapacitors. We examine the ionic conduction pathways in single crystal SrCl₂, which is a fast-ion conductor above 900~K, using four-dimensional Quasi-Elastic Neutron Scattering (4D-QENS). We explore both coherent and incoherent neutron scattering at temperatures above the transition temperature into the superionic phase to explore the correlated motion of hopping anions. Refinements of the incoherent QENS yield residence times and jump probabilities between lattice sites in good agreement with previous studies, confirming that ionic hopping along nearest-neighbor directions is the most probable conduction pathway. However, the ability to measure the coherent QENS over a large volume in reciprocal space reveals evidence of de Gennes narrowing, indicating the importance of ionic correlations in the conduction mechanism which can be compared against molecular dynamics simulations and 3-dimensional differential pair distribution function analysis of the crystal. This highlights the evolution of neutron diffraction for probing ionic transport.