Solid electrolytes—the beta aluminas

Abstract
Electrolytes conduct electricity by the movement of ions, whereas metals conduct by the flow of electrons. Until recently, almost all electrolytes known to have high conductivities were liquids, such as molten salts or aqueous solutions of salts. But research over the last twenty years has uncovered many solid electrolytes—substances that have a high ionic conductivity even though they are insulators to the flow of electrons. Physicists often call these solids “superionic conductors” because a number of the compounds have electrical conductivities comparable with those of liquid electrolytes. (But we will avoid this term to prevent a possible mistaken identification with superconductors.)