Raman Scattering Study of Structural Phase Transitions in the Iron-Substituted of Bismuth Pyrostannat/Mullite Composite

The relative influence of two different crystal structures of the composite compound Bi₂(Sn_0.7Fe_0.3)₂O₇/Bi₂Fe₄O₉ with a ratio of 91/9% studied using Raman scattering method. The Raman spectra were studied in the temperature range 93–520 K and the frequency range 1–2000 cm^–1. The types of lattice vibrations are determined. A decrease of the frequency of Raman spectra modes was found in the regions of phase transitions Bi₂(Sn_0.7Fe_0.3)₂O₇ and Bi₂Fe₄O₉. A new mode 406 cm^–1 has been established, which is a mixed oscillation of SnO₆ in Bi₂(Sn_0.7Fe_0.3)₂O₇ polyhedra (F_2g) at a frequency 400 cm^–1 and stretching vibrations of the FeO₆ octahedral at a frequency 426 cm^–1 Bi₂Fe₄O₉.