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(Sn0.7Fe0.3)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(Sn0.7Fe0.3)2O7 and Bi2Fe4O9. A new mode 406 cm–1 has been established, which is a mixed oscillation of SnO6 in Bi2(Sn0.7Fe0.3)2O7 polyhedra (F2g) at a frequency 400 cm–1 and stretching vibrations of the FeO6 octahedral at a frequency 426 cm–1 Bi2Fe4O9.