Structural, Raman, and Dielectric Studies on Multiferroic Mn‐doped Bi 1− x L a x FeO 3 Ceramics

Multiferroic Bi 1− x L a x FeO 3 [ BLFO ( x )] ceramics with x = 0.10–0.50 and Mn‐doped BLFO ( x = 0.30) ceramics with different doping contents (0.1–1.0 mol%) were prepared by solid‐state reaction method. They were crystallized in a perovskite phase with rhombohedral symmetry. In the BLFO ( x ) system, a composition ( x )‐driven structural transformation ( R 3 c → C 222) was observed at x = 0.30. The formation of Bi 2 Fe 4 O 9 impure phase was effectively suppressed with increasing the x value, and the rhombohedral distortion in the BLFO ceramics was decreased, leading to some Raman active modes disappeared. A significant red frequency shift (~13 cm −1 ) of the Raman mode of 232 cm −1 in the BLFO ceramics was observed, which strongly perceived a significant destabilization in the octahedral oxygen chains, and in turn affected the local FeO 6 octahedral environment. In the Mn‐doped BLFO ( x = 0.30) ceramics, the intensity of the Raman mode near 628 cm −1 was increased with increasing the Mn‐doping content, which was resulted from an enhanced local Jahn–Teller distortions of the ( Mn,Fe ) O 6 octahedra. Electron microscopy images revealed some changes in the ceramic grain sizes and their morphologies in the Mn‐doped samples at different contents. Wedge‐shaped 71° ferroelectric domains with domain walls lying on the {110} planes were observed in the BLFO ( x = 0.30) ceramics, whereas in the 1.0 mol% Mn‐doped BLFO ( x = 0.30) samples, 71° ferroelectric domains exhibited a parallel band‐shaped morphology with average domain width of 95 nm. Dielectric studies revealed that high dielectric loss of the BLFO ( x = 0.30) ceramics was drastically reduced from 0.8 to 0.01 (measured @ 10 4 Hz) via 1.0 mol% Mn‐doping. The underlying mechanisms can be understood by a charge disproportion between the Mn 4+ and Fe 2+ in the Mn‐doped samples, where a reaction of Mn 4+ + Fe 2+ →Mn 3+ + Fe 3+ is taken place, resulting in the reduction in the oxygen vacancies and a suppression of the electron hopping from Fe 3+ to Fe 2+ ions effectively.