Crystal structure and Ag+ conductivity of the solid electrolyte Ag8I4V2O7

The crystalline silver ion conductor A(g8)I(4)V(2)O(7) has recently been identified as the annealing product of the ion conducting glass 4 AgI - 2 Ag2O - V2O5. Single crystals of the same compound are synthesised directly from the melt. Ag8I4V2O7 crystallises in P (6) over bar 2m (No. 189) with a = 12.595(2) Angstrom, c = 9.119(2) Angstrom and Z = 3. The crystal structure is refined to a residual R(1) = 0.040 for 498 unique reflections with F-o greater than or equal to 4 sigma(F-o) and sin theta/lambda less than or equal to 0.60 Angstrom(-1). The Ag+ ion conductivity in the crystalline phase is determined by impedance spectroscopy and compared with previous work on glassy and partially crystalline samples of the same composition. Conduction pathways for the silver ions are derived from a valence sum model. Models for Ag transport in the glassy phases are discussed in the light of our results.