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Journal of Experimental and Theoretical Physics

, Volume 123, Issue 3, pp 452–460 | Cite as

Analysis of the crystal lattice instability for cage–cluster systems using the superatom model

  • D. A. SerebrennikovEmail author
  • E. S. Clementyev
  • P. A. Alekseev
Solids and Liquids

Abstract

We have investigated the lattice dynamics for a number of rare-earth hexaborides based on the superatom model within which the boron octahedron is substituted by one superatom with a mass equal to the mass of six boron atoms. Phenomenological models have been constructed for the acoustic and lowenergy optical phonon modes in RB6 (R = La, Gd, Tb, Dy) compounds. Using DyB6 as an example, we have studied the anomalous softening of longitudinal acoustic phonons in several crystallographic directions, an effect that is also typical of GdB6 and TbB6. The softening of the acoustic branches is shown to be achieved through the introduction of negative interatomic force constants between rare-earth ions. We discuss the structural instability of hexaborides based on 4f elements, the role of valence instability in the lattice dynamics, and the influence of the number of f electrons on the degree of softening of phonon modes.

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Copyright information

© Pleiades Publishing, Inc. 2016

Authors and Affiliations

  • D. A. Serebrennikov
    • 1
    Email author
  • E. S. Clementyev
    • 1
    • 2
  • P. A. Alekseev
    • 3
    • 4
  1. 1.“Functional Nanomaterials” Scientific–Educational CenterI. Kant Baltic Federal UniversityKaliningradRussia
  2. 2.Institute for Nuclear ResearchRussian Academy of SciencesMoscowRussia
  3. 3.“Kurchatov Institute” National Research CenterMoscowRussia
  4. 4.“MEPhI” National Research Nuclear UniversityMoscowRussia

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