Dynamics of boron nanoclusters in RB12 ( R = Yb, Lu) systems.

The phonon dispersion in RB₁₂ ( R = Yb, Lu) systems is studied in detail using inelastic neutron scattering over a wide range of energies (up to 55 meV). It is demonstrated that the main features of the lattice dynamics in the RB₁₂ crystals can be described in terms of a simple model of force constants with a strong hierarchy of interatomic interactions in the systems: B-B ≫ B- R ≫ R- R. An interesting feature of the low-energy portion of the phonon spectrum is the weakly dispersive optical mode. According to the model calculations, this mode is associated with the relative displacements and “breathing” vibrations of the boron nanoclusters B₁₂. [ABSTRACT FROM AUTHOR]