Ab initio study of the structure and chemical bonding of stable Ge3Sb2Te6

Abstract

The atomic arrangements and chemical bonding of stable Ge₃Sb₂Te₆, a phase-change material, have been investigated by means of ab initio total energy calculations. The results show that an ordered stacking of Ge–Te–Ge–Te–Sb–Te–Te–Sb–Te–Ge–Te– is the most stable configuration in respect that the –Sb–Te–Te–Sb– configuration enhances the structure stability as analyzed by electron localization function (ELF) and bond energies. Ge₃Sb₂Te₆ shows the character of a p-type semiconductor as seen from the density of states. The chemical bonding of Ge₃Sb₂Te₆ is rather inhomogeneous; strong and weak covalence coexist between Te and Sb atoms, while the strength of the covalent bonding between Te and Ge atoms of various Te–Ge bonds is very close, whereas the interaction between the neighboring Te layers is a van der Waals-type weak bond. The bonding character of Ge₃Sb₂Te₆ is assumed to be applied to the other pseudobinary nGeTe·mSb₂Te₃ phase-change materials.