Information storage requires that the relevant material exists in two states with a contrast in his physical properties (e. g. optical or electrical contrast).  We analyse the fundamental mechanisms that drive the structural transitions in Phase Change Materials (PCM), most of them being tellurium-based materials. We show that their special electronic properties lead to structural instabilities, called the Peierls instabilities. We analyze their relevant parameters and we establish structural maps that serve as guides for the optimization of the composition of the PCM.

Finally, we show that the understanding of covalent materials with a negative thermal expansion sheds some light on the behavior of the PCM.