Ferroelectric Origin and Distortion Modes in Doped BiFeO <sub>3</sub> by Crystallography Approach

Abstract

There are conflicts about ferroelectric origin and relationship of two distortion modes, namely, ferroelectric (FE) mode and antiferrodistortive (AFD) mode. Here two distortion modes and enhanced ferroelectric properties (Pr=89.5 μC cm-2) are observed in BiFeO3 thin films doped with small radius Mg2+ (A-site) deposited on (111) Pt/Ti/SiO2/Si substrates by a sol-gel method, relationship of two distortion modes turns from cooperative to competitive as FE mode strengthens. A new explanation of ferroelectric origin and distortion modes in doped BiFeO3 by Defect Dipoles Driven Distortions Theory (abbreviate DDD) from crystallography is reported. Meanwhile, crystal structure regulation mechanism of doped BiFeO3 thin films with substantially enhanced ferroelectric properties is also put forward. The distances of positive and negative charge center in [FeO6] octahedrons evidently increase by Mg2+ doping compared with that in Bi0.9Sm0.1Fe0.95Mn0.05O3 (BSFMO). The change of distances is contributed to law of atomic migration from move of oxygen vacancies and attraction of defect dipoles. A positive effect on ferroelectric properties of appropriate increase in oxygen vacancies is explored, which is explained by the probability of possible position that oxygen vacancies occurred and the relationship between leakage current and overlapping oxygen positions. The potential structure and more suitable doping ions are successfully predicted by crystal structure regulation mechanism. In addition, it brings a new direction for search of other structure regulation ions so as to realize perfect ferroelectric properties for practical application, which will become an important beginning of ferroelectric materials design.