Insights into the Structure of the Stable and Metastable (GeTe)m(Sb2Te3)n Compounds
Using first-principles calculations, we identify the mechanisms that lead to the lowest energy structures for the stable and metastable (GeTe){sub m}(Sb{sub 2}Te{sub 3}){sub n} (GST) compounds, namely, strain energy release by the formation of superlattice structures along of the hexagonal [0001] direction and by maximizing the number of Te atoms surrounded by three Ge and three Sb atoms (3Ge-Te-3Sb rule) and Peierls-type bond dimerization. The intrinsic vacancies form ordered planes perpendicular to the stacking direction in both phases, which separate the GST building blocks. The 3Ge-Te-3Sb rule leads to the intermixing of Ge and Sb atoms in the (0001) planes for Ge{sub 3}Sb{sub 2}Te{sub 6} and Ge{sub 2}Sb{sub 2}Te{sub 5}, while only single atomic species in the (0001) planes satisfy this rule for the GeSb{sub 2}Te{sub 4} and GeSb{sub 4}Te{sub 7} compositions. Furthermore, we explain the volume expansion of the metastable phase with respect to the stable phase as a consequence of the different stacking sequence of the Te atoms in the stable and metastable phases, which leads to a smaller Coulomb repulsion in the stable phase. The calculated equilibrium lattice parameters are in excellent agreement with experimental results and differ by less than 1% from the lattice parameters derived from a combination of the GeTe and Sb{sub 2}Te{sub 3} parent compounds.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1023071
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 78, Issue 22, 2008; Related Information: Article No. 224111
- Country of Publication:
- United States
- Language:
- English
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