Order-Disorder Transition driven Superionic Conduction in the New Plastic Polymorph of Na4P2S6

21 December 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Sodium thiophophates are promising materials for large-scale energy storage applications benefiting from high ionic conductivities and the-political abundance of the elements. A representative of this class is Na4P2S6, which currently shows two known polymorphs–α and β. This work describes a third polymorph of Na4P2S6, γ, that forms above 580◦C, exhibits fast ion conduction with low activation energy, and is mechanically soft. Based on high-temperature diffraction, pair distribution function analysis, thermal analysis, impedance spectroscopy, and ab initio molecular dynamic calculations, γ-Na4P2S6 is identified to be a plastic crystal, characterized by dynamic orientational disorder of the P2S64– anions on a translationally fixed body centered cubic lattice. The prospect of stabilizing plastic crystals at operating temperatures of solid-state batteries and benefiting from their high ionic conductivities as well as mechanical properties could have a strong impact in the field of solid-state battery chemistry.


plastic crystals
phase tranistion
ionic conductivity
real-space structure

Supplementary materials

Supporting Information
Additional details on diffraction experiments, Raman spectroscopy, pair distribution function analysis, impedance spectroscopy, photographs of impedance samples, and AIMD simulation results.


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