SELECTED PROPERTIES OF LATTICE-DYNAMICS OF HGSE AND BETA-HGS

Optical phonon dispersion for beta-HgS was measured by the neutron sca ttering for the first time. The results confirmed theoretically predic ted anomalous behavior of phonon modes in this material, resulting pro bably from high ionicity of mercury sulphide and large difference of H g and S atomic mass. Influence of the isotopic effects on the TO-phono n mode for HgSe and HgS is analysed. The possible observation of such effects in IR reflectivity spectra taken for HgSe at low temperature i s discussed.