Lattice mismatch effect on biaxial strain exerted on epitaxially-grown BiFeO_3

摘要

Lattice mismatch-induced biaxial strain effect on the crystal structure and growth mechanism have been investigated. [Fig. 1] for the BiFeO_3 thin films grown on La_(0.6)Sr_(0.4)MnO_3/SrTiO_3 and YAlO_3 substrates. Nano-beam electron diffraction (NBED), structure factor calculation and X-ray reciprocal space mapping (XRSM) 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 turns out to be relaxed at the interface by introducing dislocations. The present result demonstrates the importance of: (1) identifying the epitaxial relationship between BFO and its substrate material to quantitatively evaluate the amount of the lattice strain within BFO and (2) the atomistically coherent BFO/substrate interface for the lattice mismatch to exert the lattice strain.