Superionic Li diffusion and Anharmonic Phonons in Li2InxSc0.666−xCl4 (0 ≤ x ≤ 0.666)

Li2InxSc0.666−xCl4 (0 ≤ x ≤ 0.666) is a solid-electrolyte that has shown great potential. Our large-scale molecular dynamics simulations based on a machine-learned force field indicate that this compound exhibits superionic behavior, with calculated diffusion coefficients of 10-6 cm2/sec above 400 K. We plan to perform inelastic neutron scattering and quasi-elastic neutron scattering measurements on the compound, specifically Li2InxSc0.666−xCl4 (x=0.333), to study its Li-diffusion behavior and lattice dynamics. The ab initio calculated activation energy for the diffusion of Li in Li2InxSc0.666−xCl4 is about 0.33 eV, indicating that the compound is likely to have higher ionic conductivity and lower conduction temperature, resulting in significant QENS broadening (> 20 microeV). Our previous studies on Na/Li-based superionic conductors have shown that anharmonic lattice dynamics are important for the onset of diffusion in these systems. However, Li2InxSc0.666−xCl4 (x=0.333) exhibits superionic behavior at near room temperature, making it a particularly interesting material for further study. We expect that at elevated temperatures (700K and 900K), the fast-Li diffusion will lead to significant changes in the vibrational spectra, and will be strongly manifested in the QENS signal. The INS and QENS data on Li2In0.333Sc0.333Cl4 would be useful to know the role of lattice dynamics on lithium diffusion, the nature of diffusion, jump length, and the corresponding activation energy.