Phase change materials: The importance of resonance bonding

Phase change materials possess a property portfolio which is attractive for storage applications. At the same time the unique material properties provide interesting challenges for our understanding of solids. In this paper it will be demonstrated that many of the unique features of this material class are attributed to the bonding in the crystalline state. Resonance bonding is shown to be responsible for the high electronic polarizabilities in the crystalline state which enable a pronounced change of optical properties upon crystallization. Since resonance bonding can only develop in a very small number of solids under well‐defined conditions a map can be constructed which helps in locating phase change materials.