[10a-PA3-1~10] 6.1 Ferroelectric thin films

[10a-PA3-6] Lattice mismatch effect on biaxial strain exerted on epitaxially-grown BiFeO₃

〇Hiroshi Naganuma⁵, In-Tae Bae^1,2, Sintaro Yasui³, Mitsuru Ito³, Takahisa Shiraishi⁴, Takanori Kiguchi⁴, Tomohiro Ichinose⁵ (1.S3IP, State Univ. NY, 2.Dep.Phys. State Univ. NY, 3.LMS TIT, 4.IMR Tohoku Univ, 5.Tohoku Univ)

Keywords:Multiferroics, Structural analysis, Transmission electron microscopy

Lattice mismatch-induced biaxial strain effect on the crystal structure and growth mechanism have been investigated. [Fig. 1] [1-3] for the BiFeO₃ thin films grown on La_0.6Sr_0.4MnO₃/SrTiO₃ and YAlO₃ 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 BiFeO₃ 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 BiFeO₃ grown on La_0.6Sr_0.4MnO₃/SrTiO₃ is exerted as biaxial in-plane compressive strain with atomistically coherent interface, the ~6.8% of the lattice mismatch found in the BiFeO₃ grown on YAlO₃ 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.