ABSTRACT
This chapter focuses on role that defects play in fast ion conductors and uses the information to explain the mechanisms by which devices which rely on the materials operate. Careful manipulation of the defect populations present in ‘normal’ crystals have led to the production of a number of materials which do have ionic conductivities in the solid state which are as large as that normally found in solutions. Such materials are sometimes called super ionic conductors, but the term fast ion conductors is preferred to avoid confusion with metallic superconductors, which transport electrons, not ions, and by a quite different mechanism. The technological importance of the materials lies in the fact that they are fast ion conductors for oxygen ions at moderate temperatures. Fast ion conductors have mainly featured as solid electrolytes. When the supply of reactants on each side of the electrolyte has been exhausted the chemical reaction stops and the battery will no longer serve a useful purpose.
