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Mn- and Co-BiFeO3 polycrystalline films were prepared by a chemical solution deposition (CSD) method and their structures were investigated by grazing incidence X-ray diffraction (GIXRD) and θ–2θ XRD in conjunction with transmission electron microscopy (TEM). GIXRD measurement revealed that the Mn-BiFeO3 film contains the Bi2Fe4O9 pyrochlore phase, which might be attributed to the low magnetization of the Mn-BiFeO3 film. For the Co-BiFeO3 film, secondary phases were not observed by structural analyses and the composition was almost homogeneous. From the analytic aspect of the structure, the magnetization enhancement in the Co-BiFeO3 films is considered to be associated with Co substitution for Fe in BiFeO3.

BiFeO3 (BFO) films were formed on (001), (110), and (111) La-doped SrTiO3 single-crystal substrates. All the films were epitaxially grown and had mainly rhombohedral structure. The BFO film formed on the (001) substrate had only a (001) component whereas the BFO films on (110) and (111) substrates had (110) and (111) components, respectively. The (001), (110), and (111) epitaxial BFO films showed the remanent polarizations of 63, 84, and 106 µC/cm2, respectively. It seems that the (110) and (111) components were changed to (110) and (111) ones, respectively, by applying an external voltage. The (001) epitaxial BFO film showed marked asymmetry in its electrical properties. It was found that the (001) epitaxial BFO film had a thin tetragonal layer with spontaneous polarization fixed in the downward direction near the substrate. Finally, we concluded that this tetragonal layer caused the accumulation of space charges at the interface, causing a downward built-in field to be generated. The downward build-in field facilitated the switching of upward polarization and caused asymmetric relaxation.