A Raman scattering study of the structural ordering in Bi1–x La x FeO3 ceramic ferroelectromagnetics

Abstract

Based on Raman spectra, we have studied structural ordering processes in ceramics of ferroelectromagnetics Bi1–xLaxFeO3 (x = 0.075–0.20). It has been found that the structure of Bi1–xLaxFeO3 is close to the structure of the crystal BiFeO3. However, lines in Raman spectra of Bi1–xLaxFeO3 are considerably broadened compared to lines in the Raman spectrum of the BiFeO3 single crystal, which indicates that the structure of solid solutions is much more disordered. In Raman spectra of Bi1–xLaxFeO3, in the range of librational vibrations of octahedra as a whole (50–90 cm–1), several groups of lines are observed in frequency ranges 59–69, 72–77, and 86–92 cm–1 (depending on the composition of solid solution). This confirms X-ray data that examined solid solutions are not single-phase. At a La content x = 0.120, Raman lines in the low-frequency spectral range narrow, which indicates that the ordering of structural units in cationic sublattices somewhat increases. Upon an increase in the content of La in the Bi1–xLaxFeO3 structure, no unambiguous dependence of parameters of spectral lines is observed. It is likely that this is explained by the fact that, as the value of x increases, the character of the incorporation of La into the structure of the solid solution changes.