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.