Structural Distortion, Spin-Phonon Coupling, Interband Electronic Transition, and Enhanced Magnetization in Rare-Earth-Substituted Bismuth Ferrite

Optimizing electro-strain via manipulating the oxygen octahedral structure in BF-BT-based ceramics

Much attention has been paid to the electrical performance caused by doping, while the property regulation mechanism of intrinsic contributions such as symmetry and tilt of the oxygen octahedron is still deficiently understood in bismuth ferrite-barium titanate (BF-BT) ceramics. To establish the correlation between the evolution of the intrinsic structure and electro-strain, three doping systems of BF-BT-xLiNbO₃/xNaNbO₃/xKNbO₃ are designed, in which Li⁺, Na⁺, and K⁺ have similar chemical properties but different ionic radii. Macro-property characterization suggests that the largest electro-strain (S ∼ 0.25%) could be achieved in the BF-BT-xNaNbO₃ system when x = 0.02. Microscopic crystal structure analysis manifests that Na⁺ can enhance the symmetry of O-O and Fe-O bond lengths and maintain a certain degree of oxygen octahedron tilt, while smaller (Li⁺) and larger (K⁺) ionic radii can induce the asymmetry of O-O and/or Fe-O bond lengths. The real-space domain images indicate that the domain configuration of ceramics with improved strain exhibit similar miniaturized maze-like structures. Therefore, the synergic contributions, including symmetry of the bond length and appropriate oxygen octahedron tilt as well as miniaturized maze-like domain structure, were the origin of the improved electro-strain in BF-BT-0.02NaNbO₃. We believe that understanding the effect of the intrinsic crystal structure on the electro-strain is meaningful for tailoring BF-BT electrical properties.

Role of cooperative factors in the photocatalytic activity of Ba and Mn doped BiFeO3 nanoparticles

The escalated photocatalytic (PC) efficiency of the visible light absorber Ba-doped BiFe0.95Mn0.05O3 (BFM) nanoparticles (NPs) as compared to BiFeO3 (BFO) NPs is reported for the degradation of the organic pollutants rhodamine B and methyl orange. 1 mol% Ba-doped-BFM NPs degrade both dyes within 60 and 25 minutes under UV + visible illumination, respectively. The Ba and Mn co-doping up to 5 mol% in BFO NPs increases the specific surface area, energy of d-d transitions, and PC efficiency of the BFO NPs. The maximum PC efficiency found in 1 mol% Ba doped BFM NPs is attributed to a cooperative effect of factors like its increased light absorption ability, large surface area, active surface, reduced recombination of charge carriers, and spontaneous polarization to induce charge carrier separation. The 1 mol% Ba and 5 mol% Mn co-incorporation is found to be the optimum dopant concentration for photocatalytic applications. These properties of co-doped BFO NPs can, e.g., be exploited in the field of water splitting.