Structural origins of the unusual thermal stability of amorphous CuGe_50-Te₅₀(0⩽x⩽33.3)

We have investigated the local atomic structures of several compositions of the amorphous phase of the system CuGe50-xTe₅₀(0⩽x⩽33.3), based on extended x-ray absorption fine-structure as well as anomalous x-ray scattering experiments, and discuss the unusual trend regarding their thermal stability as a function of the Cu content. At low concentrations (x⩽15), Cu atoms tend to agglomerate in flat nanoclusters reminiscent of the crystalline phase of metallic Cu, leading to a more and more Ge-deficient Ge-Te host network structure with growing Cu content and an increasing thermal stability. At higher Cu concentrations (x⩾25), Cu is incorporated into the network, leading to an overall weaker bonding situation which is associated with a decreasing thermal stability.