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Raman spectroscopy study of sillenites. I. Comparison between Bi12(Si,Mn)O20 single crystals

1999; Elsevier BV; Volume: 60; Issue: 11 Linguagem: Inglês

10.1016/s0022-3697(99)00194-8

1879-2553

Boriana Mihailova, M. Gospodinov, L. Konstantinov,

Zeolite Catalysis and Synthesis

The Raman spectrum of Bi12(Bi0.53Mn0.47)O20 single crystal with sillenite structure was measured and compared with Raman spectra of two other sillenites, Bi12SiO20 and Bi12(Si0.98Mn0.02)O20. The peaks observed in the spectra of these sillenites are identified on the basis of calculated vibrational modes of a cluster of 33 atoms forming the set necessary to generate the crystal structure by translation symmetry operators. The results show that the peaks in the spectral range 250–350 cm−1, which result from the modes of symmetry A and are dominated by vibrations of O1 and O2 atoms, are very sensitive to the geometry of the BiOn polyhedra. The vibrational modes of the tetrahedral units are strongly influenced by the Bi–O framework. The observed splitting of the anti-symmetric tetrahedral mode in sillenites can be provoked by imperfections in Bi-occupied positions.