Understanding charge transport in phase change materials is crucial to extend the application range of these exciting materials. With this goal in mind, we have studied the resistivity and the thermal transport of crystalline phase change materials. A pronounced dependence of the room temperature resistivity upon annealing temperature is observed for crystalline phase change materials such as Ge1Sb2Te4 or Ge2Sb2Te5. This finding is corroborated by low temperature measurements as well as FTIR data, which confirm that a metal - insulator transition is observed without a change in crystallographic state. This is indicative for an electronically driven MIT. A similar transition is also observed for the thermal conductivity.
Anderson has shown that increasing disorder turns a metal with delocalized electronic states at the Fermi energy into an insulator with localized states. In this talk, arguments for a disorder induced localization of charge carriers will be presented. The observations are compared with doped semiconductors such as Si:P, where both disorder and correlations are crucial to describe the charge transport. Experimental and theoretical attempts to unravel the origin of disorder induced localization will be presented. These calculations reveal that it is the ordering of vacancies into vacancy layers which drives the transition to the metallic state . This vacancy ordering also has a pronounced impact on the thermal conductivity. The potential of this remarkable impact of disorder for applications as well as our fundamental understanding of solids is discussed.
 T. Siegrist et al., Nature Materials 10, 202, (2011)
 W. Zhang et al., Nature Materials, 11, 952 (2012).