Anomalous vibrational dynamics in the Mg2Zn11 phase

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Abstract

We present a combined experimental and theoretical study of the structure and the lattice dynamics in the complex metallic alloy Mg2Zn 11, by means of neutron and x-ray scattering, as well as ab initio and empirical potential calculations. Mg2Zn11 can be seen as an intermediate step in structural complexity between the simple Laves-phase MgZn2 on one side, and the complex 1/1 approximants and quasicrystals ZnMgAl and Zn(Mg)Sc on the other. The structure can be described as a cubic packing of a triacontahedron whose center is partially occupied by a Zn atom. This partially occupied site turned out to play a major role in understanding the lattice dynamics. Data from inelastic neutron scattering evidence a Van Hove singularity in the vibrational spectrum of Mg2Zn11 for an energy as low as 4.5 meV, which is a unique feature for a nearly-close-packed metallic alloy. This corresponds to a gap opening at the Brillouin zone boundary and an interaction between a low-lying optical branch and an acoustic one, as could be deduced from the dispersion relation measured by inelastic x-ray scattering. Second, the measured phonon density of states exhibits many maxima, indicating strong mode interactions across the whole energy range. The origin of the low-energy modes in Mg2Zn11 and other features of the vibrational spectra are studied, using both ab initio and empirical potential calculations. A detailed analysis of vibrational eigenmodes is presented, linking features in the vibrational spectrum to atomic motions within structural building blocks.

Details

Authors
  • H. Euchner
  • M. Mihalkovič
  • F. Gähler
  • M. R. Johnson
  • H. Schober
  • S. Rols
  • E. Suard
  • A. Bosak
  • S. Ohhashi
  • A. P. Tsai
  • S. Lidin
  • C. Pay Gomez
  • J. Custers
  • S. Paschen
  • M. De Boissieu
External organisations
  • University of Stuttgart
  • Grenoble Institute of Technology
  • Institute of Physics, Slovak Academy of Sciences
  • Bielefeld University
  • Institut Laue Langevin
  • European Synchrotron Radiation Facility
  • Tohoku University
  • Stockholm University
  • Uppsala University
  • Vienna University of Technology
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Materials Chemistry
Original languageEnglish
Article number144202
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume83
Issue number14
Publication statusPublished - 2011 Apr 7
Publication categoryResearch
Peer-reviewedYes