K. Kunc

Normal modes of vibrations in ZnSe

Abstract Phonon dispersion curves of ZnSe have been measured at room temperature in the [001], [110] and [111] directions using the inelastic neutron scattering. The results are interpreted in terms of rigid ion model.

MgB2 under pressure : phonon calculations, Raman spectroscopy, and optical reflectance

The effect of pressure on optical phonon frequencies of MgB2 has been calculated using the frozen-phonon approach based on a pseudopotential method. Gruneisen parameters of the harmonic mode frequencies are reported for the high-frequency zone-centre E2g and B1g and the zone-boundary E2u and B2u modes at A. Anharmonic effects of phonon frequencies and the implications of the calculated phonon frequency shifts for the pressure dependence of the superconducting transition temperature of MgB2 are discussed. Also reported are Raman and optical reflectance spectra of MgB2 measured at high pressures. The experimental observations in combination with calculated results indicate that the broad spectral features that we observed in the Raman spectra at frequencies between 500 and 900 cm-1 cannot be attributed to first-order scattering by zone-centre modes, but originate in part from a chemical species other than MgB2 at the sample surface and in part from a maximum in the MgB2 phonon density of states. Low-temperature Raman spectra taken at ambient pressure showed increased scattering intensity in the region below 300 cm-1.

Effect of pressure on the Raman modes of antimony

The effect of pressure on the zone-center optical phonon modes of antimony in the A7 structure has been investigated by Raman spectroscopy. The A(g) and E-g frequencies exhibit a pronounced softening with increasing pressure, the effect being related to a gradual suppression of the Peierls-like distortion of the A7 phase relative to a cubic primitive lattice. Also, both Raman modes broaden significantly under pressure. Spectra taken at low temperature indicate that the broadening is at least partly caused by phonon-phonon interactions. We also report results of ab initio frozen-phonon calculations of the A(g) and E-g mode frequencies. The presence of strong anharmonicity is clearly apparent in calculated total energy versus atom displacement relations. Pronounced nonlinearities in the force versus displacement relations are observed. Structural instabilities of the Sb A7 phase are briefly addressed in the Appendix.

Crystal structure and lattice dynamics of AlB2 under pressure and implications for MgB2

The effect of high pressures, up to 40 GPa, on the crystal structure and lattice dynamics of

Stress theorem in the determination of static equilibrium by the density functional method

{\mathrm{AlB}}_{2}

Local approach to polarizabilities and trends in the Raman spectra of semiconductors

was studied by synchrotron x-ray powder diffraction, Raman spectroscopy, and first-principles calculations. There are no indications for a pressure-induced structural phase transition. The Raman spectra of the metallic sample exhibit a well-defined peak near

Structure and static properties of indium nitride at low and moderate pressures

980{\mathrm{cm}}^{\ensuremath{-}1}

The lattice dynamics of gallium phosphide

at 0 GPa, which can be attributed to the Raman-active

The lattice dynamics of indium pnictides

{E}_{2g}

Ground state properties of the group IV ionic compound silicon carbide

zone-center phonon. Al deficiency of