Interplay of cation order in the superionic conductor NASICON
How to improve Na-transport in a solid electrolyte
2021/03/21 by K. Albe
In this work, the influence of different cation order on the sodium diffusivity in Na3Zr2Si2PO12 was investigated.
An ideal cation order exhibiting extraordinarily high diffusivity was identified, if all phosphorus ions were arranged on diagonals equidistant to all sodium diffusion channels. Planar alignment of the P ions, resulting in pure phosphorus and pure silicon layers stacked along the z-direction, on the other hand, was demonstrated to be detrimental for the sodium diffusivity.
Contrary to many other superionic conductor systems, our molecular dynamics simulations show that cation disorder is not generally improving the ionic conductivity in case of the NASICON crystal structure. While disorder enhances the conductivity with respect to a planar arrangement of phosphorous ions, a configuration with diagonally aligned phosphorous ions will increase the conductivity even more. We expect that this result is not particular to the Na3Zr2Si2PO12 composition, but a general feature of the NASICON crystal structure.
