Influence of crystal structure disordering on ionic conductivity of Ag7+x(P1-xGex)S6 single crystals

We present a detailed study of Ag 7+x (P 1-x Ge x )S 6 ( x = 0.1; 0.25; 0.33; 0.5; 0.75) single crystals of novel superionic conductors with argyrodite structure. The single crystals on superionic conductors Ag 7+x (P 1-x Ge x )S 6 were grown by directional crystallization technique. The crystal structure of Ag 7+x (P 1-x Ge x )S 6 solid solutions was studied by the Rietveld refinement method. It was found that solid solutions crystallize in three SGs: P2 1 3 ( x = 0.1), F-43m ( x = 0.25; 0.33) and Pna2 1 ( x = 0.5; 0.75). Ag 7+x (P 1-x Ge x )S 6 solid solutions are characterized by the presence of Ag positions with partial occupancy, which is different from the initial ternary compounds. The frequency and temperature dependences of electrical conductivity were studied by electrochemical impedance spectroscopy method. The structural disordering caused by P +5 ↔Ge +4 heterovalent cationic substitution induces increasing ionic conductivity of the solid solutions by 5 orders of magnitude. The occurrence of favorable conditions for ion transport is explained using simple structural descriptors. • A new system of solid electrolytes based on argyrodites Ag 7+x (P 1-x Ge x )S 6 was studied • The homogeneity ranges and structure of three types solid solutions were determined • Applying the P 5+ ↔Ge 4+ substitution the ionic conductivity is increased by 10 4 -10 5 times • Impact of P 5+ ↔Ge 4+ substitution on crystal structure and conductivity is discussed