Resolving the crystal-structural enigmas in Na-Super Ionic Conductors (NaSICON) of type A3M2(PO4)3, based on the A = Na, Li and M = Cr, Sc,

High ionic mobility in promising solid-state electrolytes of the NaSICON – type family depend of the temperature dependent distribution of alkaline ions over different crystallographic positions within the 3-dimensionally connected channel structure of the material. Ordering phenomena towards low temperature stepwise reduce the symmetry from the highly conduction, rhombohedral R-3c aristo structure towards monoclinic structures (C2/c, Cc, P21/c, P21/n), yet most of the intermediate states are unsolved and transition phenomena not fully understood. Using a combination of in-situ single – crystal and powder X-ray diffraction measurements (200 K <= T <= 600 K), the structural phase transition sequences will be studied on 4 representative compositions. From the obtained data we will be able to develop a general model for structural phase traditions in the NaSICON family of compounds having high potential in modern energy related material science.