Investigation of local distortions in the rocksalt structure of Ge2Sb2Te4

Phase change alloys are materials with a unique combination of properties. On the one hand side they possess a pronounced contrast of optical and electrical properties between the amorphous and the crystalline state implying a considerable structural difference between these two states [1]-[3]. On the other hand the phase transformation can be very rapid even though atoms have to be rearranged considerably. This makes phase change materials highly attractive for data storage applications. While these materials are already used commercially in optical storage [4], attempts to capitalize on the pronounced contrast in electrical conductivity between the amorphous and the crystalline state are currently under way in numerous industrial laboratories [5]-[7]. Until now phase change alloys have been developed with an approach based on trial-and-error, which hinders the development and optimization of truly novel alloys. In a recent publication [8] the influence on the high number of vacancies on one lattice site of the crystalline structure has been attributed to the tendency of phase change alloys to empty anti-bonding electronic states by a removal of electrons from the lattice. In the context of this investigation it was possible to design particularly stable alloys with superior properties. Although these studies already provide important insight into the behaviour of phase change alloys the role of thermal excitations is no