Dramatically enhanced polarization in (001), (101), and (111) BiFeO 3 thin films due to epitiaxial-induced transitions

The changes induced by epitaxial constraint in ferroelectric polarization and in crystal lattice parameters of (001), (101), and (111) films, relative to that of BiFeO 3 crystals were investigated. An enhanced polarization for these films was observed. The phase-pure BiFeO 3 (BFO) thin films were grown using pulsed laser deposition technique on these single crystals. The easy axis of spontaneous polarization was found to lie close to (111), for the various oriented films. The results show that BiFeO 3 films grown on (111) have a rhombohedral structure, and films grown on (101) or (001) are monoclinically distorted from the rhombohedral structure, due to the epitaxial constraint.