Anomalous vibrational dynamics in the Mg2Zn11 phase

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

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21 Citations (Scopus)

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.

Original languageEnglish
Article number144202
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume83
Issue number14
DOIs
Publication statusPublished - 2011 Apr 7

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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