Structure of conduction channels in superionic conductors: Crystallochemical modeling

The experimental and theoretical studies of the structure of conduction cha nnels of superionic conductors are analyzed. A crystallochemical method of modeling the conduction channels is proposed in which they are treated as s ets of polyhedron Voronoi-Dirichlet sections outside of impenetrable sphere s of the rigid sublattice. The allowance for both weak flexibility of the s pheres and their mean-square displacements relative to the sublattice point s yields a channel structure that "wraps" around the Voronoi-Dirichlet poly hedron edges. Modeling the interionic potential for alpha -AgI with the hel p of equipotential surfaces suggests that the mobile-ion motion slips along the conduction channel walls. For alpha -AgI, the set of the equipotential surfaces specifies "the minimum energy trajectory" of transition into a su perionic state, while the crystallochemical "wrapping" structure correspond s to a saddle point of a multidimensional potential surface. Symmetry selec tion rules are used for predicting mechanical trajectories as allowed oscil lation modes for the tetrahedral and octahedral fragments of alpha -CuI. (C ) 2001 MAIK "Nauka/Interperiodica".