4D-QENS analysis of ionic conduction in SrCl₂

Ionic conductivity plays a role in a wide range of energy technologies such as solid-state batteries, super capacitors, and fuel cell technology. We investigated the ionic conductivity mechanisms of chlorine conduction in SrCl₂, a fast ion conductor, above its transition point at T = 1000 K, using single crystal Quasi-Elastic Neutron Scattering measurements covering volumes of reciprocal space, 4D-QENS. The Chudley-Elliott jump diffusion model uses linewidth broadening in QENS to provide insights into the mechanisms of ionic conductivity, such as average residency times and diffusion coefficients. Two different neutron beam energies, 1.55 meV and 3.6 meV, were used in our investigations; each were sensitive to incoherent and coherent scattering, respectively. The incoherent scattering showed full agreement with the model and literature measurements of SrCl₂. The linewidths of the coherent scattering showed evidence of De Gennes Narrowing, possibly due to metastable ionic correlations in the diffusion process. Additional measurements of single crystal diffuse neutron scattering analyzed using the ‘punch and fill’ method of 3D Difference Pair Distribution Functions also provide insights into possible ion conducting pathways.