Infrared and Raman spectroscopy investigations in mullite-type Bi₂(Fe_xGa_1-x)₄O₉ polycrystals

Mullite-type Bi-2(FexGa1-x)(4)O-9 (0 & LE; x & LE; 1) oxides, prepared by mecanochemical-thermal synthesis, were investigated by FTIR and Raman spectroscopies. Similarly to other mullite systems, IR (850-400 cm(-1)) and Raman bands (750-300 cm(-1)) are attributed to stretching and bending vibrations of tetrahedral and octahedral sites. A shift in the peak positions toward lower wavenumbers with the increase of iron content is observed. High-energy IR modes show only the presence of Ga-O-Ga and Ga-O-Fe/Fe-O-Ga stretching vibrations for x < 0.5. Raman bands between 500 cm(-1) and 400 cm(-1) revealed double band splitting for x < 0.5.