Structural origins of the unusual thermal stability of amorphous Cu x Ge50−x Te50 (0 ⩽ x ⩽ 33.3)

Abstract

Abstract We have investigated the local atomic structures of several compositions of the amorphous phase of the system Cu x Ge 50 − x Te50 ( 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.