Understanding the local structure of Li6PS5X (X = Cl, Br, I) and its impact on Li migration – a neutron PDF study

Cubic Argyrodites, Li6PS5X, are promising candidates for solid state electrolytes and much effort is put in understanding their structure property relation. NMR studies revealed, that within the anion sublattice, Cl- and Br- tend to be statistically distributed, while I- occupies a separate crystallographic position. It is of immediate need to understand the role of occupational defects and distortions in these materials in detail, since such structural peculiarities highly correlate with ion migration. A review of the effect of lattice distortions and ion migration barriers revealed a discrepancy between proposed mechanisms for Argyrodites and other solid state electrolytes, indicating that the defect structure is not well understood yet. Based on our early RT XPDF results, we have strong indications to believe that the understanding of the structure so far may be too simplified.