Vibrational spectra of sodium gadolinium tungstate NaGd(WO4)2 single crystals: Observation of spatial dispersion |
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Authors: | S Perets RZ Shneck R Gajic A Golubovic Z Burshtein |
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Institution: | 1. Department of Materials Engineering, Ben Gurion University of the Negev, P.O. Box 653, Beer-Sheva, Israel;2. Institute of Physics, Pregrevica 118, 11080, Belgrade, Serbia |
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Abstract: | Room temperature polarized Raman scattering and infrared reflectance spectra of a NaGd(WO4)2 single crystal have been measured. The IR spectra interpretation was aided by a Kramers-Krönig analysis, and fitted to the independent oscillator model. All 13 theoretically expected Raman-active bands have been identified and assigned, as well as 7 out of 8 expected IR active bands. Splitting of bands in both Raman and IR clearly indicates a lowering of the crystal symmetry due to occupation disorder in the 4a site, that randomly accommodates either an Na+ or a Gd3+ ion. The reflectance IR spectra reveal a spatial dispersion, namely a dependence of the transverse optical (TO) polariton frequencies, on the propagation direction in the crystal. The crystal vibrational modes are correlated to the internal modes of the tungstate group WO42?, and to the internal modes of the molecular skeleton. A detailed correlation map of the symmetry analysis is presented. |
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