Lattice dynamics in intermetallic Mg2Ge and Mg2Si

D. Bessas, R. E. Simon, K. Friese, M. Koza, R. P. Hermann

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17 Scopus citations

Abstract

The lattice dynamics of polycrystalline Mg2Ge and Mg2Si are compared using both microscopic and macroscopic measurements as well as theoretical calculations. The volume thermal expansion coefficient between 200 and 300K was found to be 4.37(5)•10-5K-1 in Mg2Ge, compared to 3.69(5)•10-5K-1 in Mg2Si. Inelastic neutron scattering measurements yield densities of phonon states which are in line with theoretical calculations. The microscopic data were corroborated with macroscopic calorimetry measurements and provide quantified values for anharmonicity. The estimated macroscopic Grneisen parameter is, γMg2Si=1.17(5) and γMg2Ge=1.46(5) at 295K, in excellent agreement with Raman scattering data. Although the element specific mean force constants are practically the same, in Mg2Ge and Mg2Si, a mass homology relation alone cannot reproduce the difference in the partial densities of vibrational states in these compounds and differences in elemental bonding should be taken into account.

Original languageEnglish
Article number485401
JournalJournal of Physics Condensed Matter
Volume26
Issue number48
DOIs
StatePublished - Dec 3 2014
Externally publishedYes

Keywords

  • antifluorite
  • lattice dynamics
  • thermoelectrics

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