OSCILLATIONS OF THE PHONON-SPECTRA DUE TO ANION-LATTICE COUPLING

The interaction of a lattice with an anion gas is investigated with th e goal of finding the effect of anion-phonon coupling on the phonon sp ectra at finite wave vectors. The interaction results in oscillations on the acoustic-phonon dispersion curves. The oscillations essentially depend on the statistical parameter and vanish in the limits of boson and fermion statistics. We study also the effect of Coulomb interacti on on the oscillation. We find that Coulomb interaction suppresses the oscillation and this effect is most essential in limit of low anion d ensities.