Structural properties of Bi_1-xLa_xFeO₃ studied by micro-Raman scattering

This paper reports that La-doped BiFeO₃ (Bi_1-xLa_xFeO₃, x=0, 0.1, 0.2, 0.3, 0.6, 0.8 and 1.0) were studied by using micro-Raman spectroscopy and x-ray diffraction (XRD). The XRD patterns indicate that the structure of Bi_1-xLa_xFeO₃ changes from rhombohedral BiFeO₃ to orthorhombic LaFeO₃. The results of Raman spectroscopy show good agreement with the XRD results. Strikingly, the phonon peak at around 610 cm^-1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution. The increasing intensity of the 610 cm^-1 peak is attributed to the changes in the FeO₆ octahedron during the rhombohedral--orthorhombic phase transition. The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure. These results indicate the existence of strong spin--phonon coupling in Bi_1-xLa_xFeO₃, which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi_1-xLa_xFeO₃.