Short range biaxial strain relief mechanism within epitaxially grown BiFeO ₃

Lattice mismatch-induced biaxial strain effect on the crystal structure and growth mechanism is investigated for the BiFeO ₃ films grown on La _0.6 Sr _0.4 MnO ₃ /SrTiO ₃ and YAlO ₃ substrates. Nano-beam electron diffraction, structure factor calculation and x-ray reciprocal space mapping unambiguously confirm that the crystal structure within both of the BiFeO ₃ thin films is rhombohedral by showing the rhombohedral signature Bragg’s reflections. Further investigation with atomic resolution scanning transmission electron microscopy reveals that while the ~1.0% of the lattice mismatch found in the BiFeO ₃ grown on La _0.6 Sr _0.4 MnO ₃ /SrTiO ₃ is exerted as biaxial in-plane compressive strain with atomistically coherent interface, the ~6.8% of the lattice mismatch found in the BiFeO ₃ grown on YAlO ₃ is relaxed at the interface by introducing dislocations. The present result demonstrates the importance of: (1) identification of the epitaxial relationship between BFO and its substrate material to quantitatively evaluate the amount of the lattice strain within BFO film and (2) the atomistically coherent BFO/substrate interface for the lattice mismatch to exert the lattice strain.