Raman spectroscopic study of benitoite-type compounds

Raman scattering measurements were performed in the benitoite-type BaTiSi₃O₉, BaZrSi₃O₉, BaSnSi ₃O₉ and tetragermanate-type BaGe₄O₉ phases in order to elucidate the spectroscopic and structural features of D _2/vG(T₃O₉)-type compounds (expressed by Smith's notation) with the GO₆ octahedral unit isolated by the T ₃O₉ ring. The Raman band assignments in middle and high wavenumber region wes also carried out. In addition, the wavenumber of antisymmetric stretching vibration mode, v_as, for Si-O-G bond was calculated by means of combination of the simple molecular model and Badger's rule, and compared with the experimental results. It was suggested that the v_as was governed by the force constant of T-O_ax bond, which was connected with the G⁴⁺.