Crystal Structure of the Solid Electrolyte(C 5 H 5 NH) Ag 5 I 6 at -30°C

Abstract

The crystal structure of pyridinium hexaiodopentaargentate, (C₅H₅NH) Ag₅l₆, is unique among those of the halide and chalcogenide solid electrolytes in that face-sharing iodide octahedra as well as face-sharing tetrahedra and face-sharing between octahedra and tetrahedra provide the paths for silver ion transport. There are two formula units in a hexagonal cell, space group P6/mcc (D_6h²). At -30°C, the lattice constants are a = 11.97 ± 0.02, c = 7.41 ± 0.01 Å. The structure has three sets of sites for the silver ions. At -30°C two of these sets are apparently filled with the ten silver ions per unit cell, while the third set of tetrahedrally coordinated general positions is empty. Therefore, the conductivity at this temperature is limited by the thermal excitation of the silver ions into the empty tetrahedra.