Ionic conductivity and solid-phase transitions in Li2SO4Li2WO4 system relating to ion transport mechanism

New insights into the mechanism of cation migration induced by cation–anion dynamic coupling in superionic conductors

“…To get prima facie common features of the systems evolved in the anion-assisted cation migration, we sort out the motion ability of anion groups which show positive effects on the diffusion of cations. 18–39 All the ions contained in these compounds can be classified into three types according to their functions in the ion transport process. The immobile cations act as the framework to stabilize the structure.…”

“…The already confirmed factors that are closely related to cation migration in solids include atomic configurations, 7–10 free volume, 11,12 and the concerted migration mechanism, 13–17 which focus on the potential energy surface (PES) around the migrating ions geometrically or the internal interactions among a series of cations. Similarly, the dynamic coupling between anion and cation motions 18–39 has been observed by quasi-elastic neutron scattering (QENS), 23,24,28–30,34 nuclear magnetic resonance (NMR) techniques 21,22,29,31,34 or simulated by molecular dynamics 24–27,33,35–38 in some lithium or sodium superionic conductors containing anion groups such as SO 4 2− , 18–20 PO 4 3− , 21–23 PS 4 3− , 24–27 B x H y z − , 28–35 XCl 6 2/3− , 36 OH − 37,38 and NO 2 − . 39 From previous experimental observations, mainly two phenomenological explanations, “paddle wheel mechanism” and “percolation mechanism”, are extracted to describe how the cation migration is assisted by the motion of anion groups.…”