Lattice dynamics in ZrB12 and LuB12: Ab initio calculations and inelastic neutron scattering measurements

The first ab initio calculations using ultrasoft pseudopotentials within the local-density approximation in superconducting ZrB12 are reported, together with an inelastic neutron scattering study of its lattice dynamics. As in previously studied rare-earth dodecaborides, the phonon spectra are mainly determined by vibrations of the rigid boron network whereas Zr atoms vibrations have a quasilocal character and are localized in a narrow energy range around E approximate to 17 meV. The results consistently indicate that the phonon modes corresponding to Zr vibrations are responsible for a considerable electron-phonon interaction and could take part in the formation of the superconducting state below T-c approximate to 6 K as was suggested previously.