Ab initio study of the structure and chemical bonding of stable Ge(3)Sb(2)Te(6).

The atomic arrangements and chemical bonding of stable Ge(3)Sb(2)Te(6), 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. Ge(3)Sb(2)Te(6) shows the character of a p-type semiconductor as seen from the density of states. The chemical bonding of Ge(3)Sb(2)Te(6) 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 Ge(3)Sb(2)Te(6) is assumed to be applied to the other pseudobinary nGeTe.mSb(2)Te(3) phase-change materials.