Lattice dynamics of alkaline-earth oxides

The crystal dynamics of some alkaline-earth oxides (MgO, CaO, SrO, and BaO) have been studied in the framework of a seven-parameter bond-bending force model (BBFM). The BBFM incorporates seven disposable parameters, which have been fixed by making use of the experimental data on elastic constants and neutron scattering and/or infrared (IR) measurements. The phonon dispersion relations have been computed at all the irreducible wave-vector points in the first Brillouin zone. The complete phonon spectra have been used to calculate the phonon density of states, which are further used to derive the temperature (T) dependence of the Debye-characteristic temperature (θD). Theoretical phonon dispersion curves along three symmetry directions and the θD–T curves have been compared with the available experimental data. It is observed that the model calculations are in a reasonably good agreement with the existing experiments. Few assignments have also been proposed for the SrO spectra by using the critical-point–phonon analysis for which not sufficient neutron and IR measurements exist.