SOLID ELECTROLYTES

The application of solid electrolytes in electrochemical cells is used as a basis for establishing quality criteria for these materials. Emphasis is given to the electrolyte window and the bulk ionic conductivity in the design of a solid electrolyte. Fast ionic conduction in stoichiometric compounds is characterized by a transition from long-range to short-range ordering that may be smooth or first-order. Smooth transitions involving cluster excitations are contrasted with first-order transitions involving ionic ordering within an array of otherwise equivalent lattice sites or a displacive transition of the fixed-ion array. Ionic conduction in doped compounds is hindered by trapping at the dopants as well as by interactions between the mobile species that introduce short-range ordering. Water absorption may plague oxide-ion electrolytes. Illustrative examples are cited.