Sodium (translational) and thiophosphate (rotational) dynamics in the plastic crystalline electrolyte Na3PS4

We have recently discovered a high-temperature polymorph of the promising Na-ion conductor, Na3PS4. The new polymorph exhibits plastic crystallinity, with very high sodium (translational) diffusivity and thiophosphate (rotational) diffusivity. These dynamics are expected to be observable by QENS, incoherent for the Na (expected in the 100s of μeV) and coherent for S (expected in the 10s of μeV). Investigating the interplay between anion and cation dynamics, and understanding the how to stabilize such plastic-crystalline ion conductors at lower temperatures would be most impactful in the context of their application as electrolytes for advanced electrochemical devices, in particular batteries.