Structure, electronic, and vibrational properties of glassy Ga11Ge11Te78: Experimentally constrained density functional study

Voleská, I.; Jovari, P.; Vasileiadis, Th.; Wágner, T.; Akola, J.; Yannopoulos, S. N.; Jones, R. O.; Gutwirth, J.

doi:10.1103/PhysRevB.86.094108

Journal Article

Structure, electronic, and vibrational properties of glassy Ga11Ge11Te78: Experimentally constrained density functional study

Voleská, I. ; Akola, J. ; Jovari, P. ; Gutwirth, J. ; Wágner, T. ; Vasileiadis, T. ; Yannopoulos, S. N. ; Jones, R. O.FZJ*

2012
APS College Park, Md.

Physical review / B 86(9), 094108 (2012) [10.1103/PhysRevB.86.094108]

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Please use a persistent id in citations: http://hdl.handle.net/2128/10843 doi:10.1103/PhysRevB.86.094108

Abstract: The atomic structure and electronic and vibrational properties of glassy Ga11Ge11Te78 have been studied by combining density functional (DF) simulations with x-ray (XRD) and neutron diffraction (ND), extended x-ray absorption fine structure (EXAFS), and Raman spectroscopies. The final DF structure (540 atoms) was refined using reverse Monte Carlo methods to reproduce the XRD and ND data as well as Ge and Ga K-edge EXAFS spectra, while maintaining a semiconducting band gap and a total energy close to the DF minimum. The local coordination of Ga is tetrahedral, while Ge has twice as many tetrahedral as defective octahedral configurations. The average coordination numbers are Ga, 4.1, Ge, 3.8, and Te, 2.6. The chemical bonding around Ga involves Ga 4s, Ga 4p, Te 5s, and Te 5p orbitals, and the bond strengths show bonding close to covalent, as in Ge. There are fewer Te chains and cavities than in amorphous Te, and a prepeak in the structure factor at 1.0 angstrom(-1) indicates medium-range order of the Ga/Ge network. Density functional calculations show that contributions of Te-Te, Ga-Te, and Ge-Te bonds dominate the experimental Raman spectra in the 110-150 cm(-1) range.

Keyword(s): J

Classification:

Physics, Condensed Matter

Note: The calculations were performed on IBM Blue Gene/P and Intel Xeon computers in the Forschungszentrum (FZ) Julich with grants from the FZ Julich and the John von Neumann Institute for Computing (NIC). J.A. acknowledges financial support from the Academy of Finland through its Centres of Excellence Program (Project No. 251748). S.N.Y. thanks G. Voyiatzis for providing the Raman facility at FORTH/ICE-HT. We are grateful for financial support from the Grants No. CZ.1.07/2.3.00/20.00254 "Research Team for Advanced Non-crystalline Materials" and No. CZ.1.07/2.3.00/30.0021 "Strengthening of Research and Development Teams at the University of Pardubice," realized by the European Social Fund and Ministry of Education, Youth and Sports of the Czech Republic within the Education for Competitiveness Operational Program. The German Research School for Simulation Sciences is a joint venture of the FZ Julich and RWTH Aachen University.

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