Controlling thermal transport in solids is of paramount importance for many applications. Often thermal management is crucial for a device's performance, as it affects both reliability and power consumption. A number of intricate concepts have been developed to address this challenge, such as diamond-like coatings to enhance the thermal conductivity or low symmetry complex super-structures to reduce it. Here, a different approach is pursued, where we explore the potential of solids with a high yet controllable degree of disorder. Recently, it has been demonstrated that an unconventionally high degree of structural disorder characterizes a number of crystalline phase-change materials (PCMs). This disorder strongly impacts electronic transport and even leads to disorder induced localization (Anderson localization). This raises the question how thermal transport is affected by such conditions. Here thermal transport in highly disordered crystalline Ge-Sb-Te (GST) based PCMs is investigated. Glass-like thermal properties are observed for several crystalline PCMs, which are attributed to strong scattering by disordered point defects. A systematic study of different compounds along the pseudo-binary line between GeTe and Sb2Te3 reveals that disordered vacancies act as point defects responsible for pronounced phonon scattering. Annealing causes a gradual ordering of the vacancies and leads to a more 'crystal-like' thermal conductivity. While both vibrational and electronic degrees of freedom are affected by disorder, the consequences differ for different stoichiometries. This opens up a pathway to tune electrical and thermal transport by controlling the degree of disorder. Materials with tailored transport properties may not only help to improve power efficiency and scaling in upcoming phase-change memories but are also of fundamental interest in the field of thermoelectric materials.

Phase‐change materials form a unique material class, characterized by a rather unusual combination of physical properties. Exhibiting fast crystallization and a large contrast in optical reflectivity and electrical conductivity between the amorphous and the crystalline state, they are ideally suited for non‐volatile data storage. Here, we present the thermoelectric properties of Ge3Sb2Te6 and Ge8Sb2Te11 phase‐change alloys measured between room temperature and 120 °C. Both systems display intrinsically high Seebeck coefficients and low thermal conductivities. While low electrical conductivities preclude the employment of Ge3Sb2Te6 in thermoelectric applications, the GeTe rich Ge8Sb2Te11 exhibits high ZTs of up to 0.7 in the temperature range investigated, which renders this alloy a potential p‐type thermoelectric material.