Phase transitions in germanium antimony tellurides and related compounds

Germanium antimony tellurides play an important role both as phase-change materials for data storage and as thermoelectric materials for the interconversion of heat and electrical energy. They are characterized by disordered cubic high-temperature phases. Upon cooling, they become rhombohedral. This can be a simple lattice distortion or a diffusion-controlled process that is associated with vacancy ordering. This leads to nanostructures with twin domains that significantly influence physical properties. These nanostructures can be influences by different cooling rates or annealing processes as wenn as by the introduction of additional chemical elements. Oriented (endotaxial) intergrowth of different crystal structure types occurs if indium is added. This adds additional possibilities for phase transitions. Synchrotron raditiation enables the in situ observation of phase transitions in a space- and time resolved manner. However, transport properties depend on a complex interplay of electronic and phononic effects.