ABSTRACT
This chapter is an introduction to the physics and chemistry of solid and liquid ion conductors. It mainly focuses on proton and oxygen-ion conducting materials, which are currently, in many cases, the key functional materials in the field of energy provision. Differences between liquid and solid electrolytes are analyzed from the perspective of fundamental parameters that govern the ionic conductivity and the dependencies of the ionic conductivity on temperature. Mechanisms of ionic conductivity in solids are explained. These mechanisms include the conductivity due to different types of defects, corporative movement of structural units of solids, and ionic conductivity originating from the existence of polymer superstructures. The ideas explaining heterogeneous and homogeneous doping to increase the ionic conductivity are provided, and relevant examples are given. The design principles of how to obtain ionic liquids with relatively low melting temperatures are briefly discussed.
