Structural and vibrational properties of (Bi1−xLax)FeO3 and (Bi1−yBay)(Fe1−yTiy)O3 multiferroic ceramics investigated by Raman scattering

Abstract

Abstract La-modified Bi 1−x La x FeO 3 (x = 0.15–0.40) and BaTiO 3 -modified (Bi 1−y Ba y )(Fe 1−y Ti y )O 3 (y = 0.10−0.33) multiferroic ceramics were synthesized via solid-state reactions, and their structural and vibrational properties were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The XRD patterns reveal that the La-modified Bi 1−x La x FeO 3 system exhibits an rhombohedral – orthorhombic structural transition at x = 0.40. The degree of rhombohedral distortion in the Bi 1−x La x FeO 3 ceramics was decreased with increasing the La content, resulting in the disappearance of some Raman active modes (e.g. A 1 -4, E (TO1), E (TO2), E (TO6)). Similarly, in the BaTiO 3 -modified (Bi 1−y Ba y )(Fe 1−y Ti y )O 3 system, a composition-driven structural transition from rhombohedral ( R 3c) phase to cubic phase appeared at y = 0.30, indicating a morphotropic phase boundary between the rhombohedral and cubic phases. It is found that the Raman mode frequencies of the A 1 -1, A 1 -2, A 1 -3 and E (TO3) modes are slightly dependence of either the La content in Bi 1−x La x FeO 3 system or the BaTiO 3 content in (Bi 1−y Ba y )(Fe 1−y Ti y )O 3 system, whereas the frequencies of the E (TO8) and E (TO9) Raman active modes are significantly dependent upon the modified compositions. Such compositional dependence of the Raman active mode frequencies are discussed and interpreted based on a spring oscillator model in combination with the structural phase transition, the degree of rhombohedral distortion, and the B–O bond length in the BO 6 octahedron. The present results are useful for understanding the correlation between the structural and physical properties of the La-modified Bi 1−x La x FeO 3 and the BaTiO 3 -modified (Bi 1−y Ba y )(Fe 1−y Ti y )O 3 ceramics.