Measurement and comparative analysis of the second-order raman spectra of the alkaline-earth oxides with a nacl structure

Measurements of the three independent components of the second-order Raman tensors of CaO, SrO, and BaO have been performed. A critical-point analysis based on the existing neutron data explains the CaO Raman spectra in detail. The similarities between the spectra of CaO and MgO are discussed. The striking resemblance of the SrO spectra to those of CaO enables us to explain the major features in the SrO spectra. Owing to systematic trends in the features of the Raman spectra of the whole family of the alkaline-earth oxides, some information about the phonon dispersion in BaO is also obtained. Qualitative aspects of the Raman spectra of the oxides as compared to those of alkali halides are discussed on the basis of a shell-model theory, including intraionic anharmonicity.