Ab initio study of the structure and chemical bonding of stable Ge ₃Sb₂Te₆

The atomic arrangements and chemical bonding of stable Ge ₃Sb₂Te₆, 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 Ge₃Sb ₂Te₆ is assumed to be applied to the other pseudobinary nGeTe·mSb₂Te₃ phase-change materials.