Large bi-axial tensile strain effect in epitaxial BiFeO film grown on single crystal PrScO.

A BiFeO film is grown epitaxially on a PrScO single crystal substrate which imparts ~ 1.45% of biaxial tensile strain to BiFeO resulting from lattice misfit. The biaxial tensile strain effect on BiFeO is investigated in terms of crystal structure, Poisson ratio, and ferroelectric domain structure. Lattice resolution scanning transmission electron microscopy, precession electron diffraction, and X-ray diffraction results clearly show that in-plane interplanar distance of BiFeO is the same as that of PrScO with no sign of misfit dislocations, indicating that the biaxial tensile strain caused by lattice mismatch between BiFeO and PrScO are stored as elastic energy within BiFeO film. Nano-beam electron diffraction patterns compared with structure factor calculation found that the BiFeO maintains rhombohedral symmetry, i.e., space group of R3c. The pattern analysis also revealed two crystallographically distinguishable domains. Their relations with ferroelectric domain structures in terms of size and spontaneous polarization orientations within the domains are further understood using four-dimensional scanning transmission electron microscopy technique.