Crystalline GeSb 2 Te 4 (GST) is a remarkable material, as it allows to continuously tune the electrical resistance by orders of magnitude without involving a structural phase transition or stoichiometric changes. While wellordered specimen are metallic, increasing amounts of disorder eventually lead to an insulating state with vanishing conductivity in the 0 K limit, but a similar number of charge carriers. Hence, GST provides ideal grounds to explore the impact of disorder on transport properties. Here, a sputterdeposition process is employed that enables growing biaxially textured GST films with large grain sizes on mica substrates. The resulting films exhibit a systematic variation between metallic and truly insulating specimen upon varying deposition temperature. Transport measurements reveal that their electron mean free path can be altered by a factor of 20, while always remaining more than an order of magnitude smaller than the lateral grain size. This proves unequivocally that grain boundaries play a negligible role for electron scattering, while intra-grain scattering, presumably by disordered vacancies, dominates. These findings underline that the insulating state and the system's evolution toward metallic conductivity are intrinsic properties of the material.

The damaging process of GeTe up to amorphization has been studied by introducing controlled levels of disorder by irradiation with 150 keV Ar + ions. In situ reflectivity measurements and exsitu resistance and Raman spectroscopy analysis have been employed to study the impact of ion bombardment on the electrical conduction properties and on the bonding. The results obtained are indicative for three different stages of film damage. The first step appears to be dominated by point defects, affecting the temperature coefficient of resistance (TCR) and inducing a transition from positive (metallic conduction) to negative TCR values (conduction dominated by localized states), whilst the material still remains crystalline. The second step is characterized by the annealing of the defects induced, presumably, by the formation of complex defects that act as sinks for point defect recombination. This process is facilitated by the high atomic mobility. The third phase of damage starts at a fluence of 3.5 × 10 14 cm −2 and finally converts the material to the amorphous state, characterized by higher resistance and decreased optical reflectivity. The modifications observed upon ion irradiation provide important insights into the possible states that can be achieved in crystalline GeTe through different local atomic arrangements towards amorphization.