Superionic Conduction in the Plastic Crystal Polymorph of Na4P2S6

Scholz, T.; Schneider, C.; Terban, M.; Deng, Z.; Eger, R.; Etter, M.; Dinnebier, R.; Canepa, P.; Lotsch, B.

doi:10.1021/acsenergylett.1c02815

Superionic Conduction in the Plastic Crystal Polymorph of Na₄P₂S₆

T. Scholz, C. Schneider, M. Terban, Z. Deng, R. Eger, M. Etter, R. Dinnebier, P. Canepa, and B. Lotsch; ACS Energy Lett. 7, 1403 (2022).

BibTeX

@article{Scholz2022superionic,
  author  = {Scholz, T. and Schneider, C. and Terban, M. and Deng, Z. and Eger, R. and Etter, M. and Dinnebier, R. and Canepa, P. and Lotsch, B.},
  title   = {{Superionic Conduction in the Plastic Crystal Polymorph of Na$_{4}$P$_{2}$S$_{6}$}},
  journal = {ACS Energy Letters},
  volume  = {7},
  pages   = {1403},
  year    = {2022},
  doi     = {10.1021/acsenergylett.1c02815}
}

Abstract

Sodium thiophophates are promising materials for large-scale energy storage applications benefiting from high ionic conductivities and the geopolitical 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 ℃, 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, the γ-Na₄P₂S₆ phase is identified to be a plastic crystal characterized by dynamic orientational disorder of the P₂S₆⁴⁻ anions translationally fixed on a body-centered cubic lattice. The prospect of stabilizing plastic crystals at operating temperatures of solid-state batteries, with benefits from their high ionic conductivities and mechanical properties, could have a strong impact in the field of solid-state battery research.