SEARCH

SEARCH BY CITATION

Keywords:

  • 02.20.−a;
  • 61.50.Ah;
  • 63.20.−e;
  • 78.30.−j

Abstract

Raman selection rules were theoretically put forward and, according to the obtained relationships, the full set of Raman tensor elements was experimentally determined for the corundum structure of a sapphire single-crystal. The knowledge of the Raman selection rules allowed us to represent the change in polarizability of the aluminium oxide molecule with respect to each of the available vibrational modes. Restrictions related to the symmetry of the scattering system are also discussed together with directional properties, thus leading to unambiguous assignment of the fundamental modes available in sapphire single-crystal. From the experimental side, scattering intensities of Raman bands located at 378 cm–1 and 417 cm–1, which correspond to the Eg and the A1g phonon modes of the corundum structure, respectively, were collected in selected polarization configurations as a function of in-plane rotation angle on different crystallographic planes. Fitting to theoretical equations (i.e., worked out for different crystallographic orientations) enabled us to unequivocally define the elements of the Raman tensor. Finally, a tensorial algorithm was proposed for the practical determination of unknown crystallographic textures in polycrystalline alumina materials, an issue of significant importance in materials science. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)