Crystal Structures and Electrical Properties of Epitaxial BiFeO_3 Thin Films with (001), (110), and (111) Orientations

摘要

BiFeO_3 (BFO) films were formed on (001), (110), and (111) La-doped SrTiO_3 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 106μC/cm~2, 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.