Intermediate range structure of amorphous Cu₂GeTe₃: ab initio molecular dynamics study

We have investigated the intermediate range structure of amorphous Cu₂GeTe₃ based on ab initio molecular dynamics simulations. The highest population of ring size is three, which makes the triangle structure. This ring consists of mainly Cu₂Te. Rings may also consist of CuCuCu, Cu₂Ge, and CuGeTe, where approximately 88% of Cu atoms in the system are related with the three-membered ring. The second highest population of ring size is five. Three- and five-membered rings in the amorphous phase originate from six-membered ring in the crystalline phase. This situation can enhance the phase transition between crystalline and amorphous phases. In the phase change process, Cu atoms may diffuse in the amorphous state with changing bonds. The diffusion coefficient of Cu D _Cu is estimated to be approximately 0.12 × 10^-9 m² s^-1. Such high diffusion coefficient of Cu atoms is contributed from only 10% of Cu atoms in the amorphous phase.