Quasi-elastic Study of Na Diffusion in Superionic Conductors Na3Sb(S,Se)4

Searching a design criteria for superionic conductors (SICs) is critical for development of next-generation all-solid-state batteries. However, a single unified theory for the origin of superionicity is still missing. Here, we propose to investigate a systematic study based on Na3PnCh4 (Pn=P, Sb; Ch=S, Se), aiming to establish useful descriptors enabling the design of future SIC materials.

Na3PnCh4 (Pn=P, Sb; Ch=S, Se) family shows potential for applications and also enables a fundamental study of ionic conduction mechanisms by varying both Pn and Ch sites. Recently, we have revealed the important interplay between mobile ion diffusion and the dynamic host lattice in Na3PS4. By combining the inelastic neutron scattering (INS), quasi-elastic neutron scattering (QENS) and first-principles simulations, we showed a link between the behavior of specific low-energy phonons of the parent phase (framework lattice dynamics) with the Na diffusion process. We would like to extend our study to other compositions to refine the ionic hopping mechanisms and clarify chemical trends in Na3PnCh4 series.

We have collected the INS data on all of four compositions but we are missing the QENS data on Na3SbS4 and Na3SbSe4. We request further beamtimes for QENS to complete our systematic study to thoroughly understand the interaction between phonon dynamics and ion diffusion.