ABSTRACT
This chapter deals with the structural diversity of solid state ionic materials (SSIMs) vis-a-vis their phase stability, often against phase transitions. Phase equilibria naturally involve thermodynamics. Among the numerous phases involving Li+, Na+, Ag+, Cu+, F−, and O= with structures from triclinic to cubic, two parameters break symmetry: cooling from a high temperature and cation substitution especially in cubic structures such as perovskites. A thorough discussion of these aspects offers a bottom line: A thermodynamically stable defect-ridden, mobile ion path-optimized superionic conductor ready for application.
