LATTICE-DYNAMICS OF CR2O3

We present the results of inelastic neutron scattering experiments for Cr2O3 carried out using the single-crystal time-of-flight spectromete r PRISMA at ISIS (U.K.) as well as the three-axis spectrometer TAS-1 a t JAERI (J). The collected data are analysed on the basis of phenomeno logical shell models showing convincing agreement between calculation and experiment both for the frequencies and intensities. All together the dispersion relations of 12 out of 20 phonon branches along the thr ee-fold axis are determined. By a comparison with the Cr2O3 iso-type s apphire (A1(2)O(3)) it is found that the dynamical response of the oxy gen ion is only little affected by the ionic substitution. The chromiu m d electrons find their expression mainly in a strengthening of the m etal-oxygen bonding. The problem of ionic polarizabilities is addresse d in detail both for the oxygen and chromium ions.