Structural aspects of fast copper mobility in CU6PS5Cl -: The best solid electrolyte from CU6PS5X series

The structural origin of fast copper conduction in Cu6PS5Cl single crystals is discussed. Cu6PS5Cl crystallises in the same cubic F (4) over bar 3m symmetry as the other Cu6PS5X's, X = Cl, I, Br. However, this phase is stabilised at much lower temperatures (down to 160 K) and is characterised by higher level of disorder in copper substructure. Complex domain structure developing at low temperatures proves that Cu6PS5Cl undergoes ferroelastic phase transition (PT) associated with cubic F (4) over bar 3m to monoclinic Cc symmetry change. The structural distortion connected with this transformation is very subtle. X-ray diffraction measurements show strong precursor phenomena below 205 K which correspond to the low temperature phase and point out to copper ordering in nano- or microscopic scale above the temperature of ferroelastic phase transition (PT). The pseudopotential based on copper joint probability density function is calculated along diffusion paths at 175 and 435 K. (C) 2008 Elsevier Inc. All rights reserved.