[19p-PA3-1~9] 6.1 Ferroelectric thin films

[19p-PA3-4] Short range biaxial strain relief mechanism within epitaxially grown BiFeO₃

In-Tae Bae¹, Shintaro Yasui², Tomohiro Ichinose³, Mitsuru Ito², Takahisa Shiraishi⁴, Takanori Kiguchi⁴, 〇Hiroshi Naganuma^3,5,7,6 (1.State Univ. NY at Binghamton, 2.LMS TIT, 3.Tohoku Univ., 4.IMR Tohoku Univ., 5.CIES Tohoku Univ, 6.CSIS Tohoku Univ., 7.CSRN Tohoku Univ.)

Keywords:Multiferroics, BiFeO3, Structural analyses

BiFeO₃ (BFO) epitaxial films change crystal symmetry on the various single crystal substrates. Although the growth mechanism depends on each substrate, there is not so many detail and systematic structural analysis using various angle of electron diffraction combined with X-ray diffraction. In this study, lattice mismatch-induced biaxial strain effect on the crystal structure and growth mechanism is investigated for the BFO films grown on La_0.6Sr_0.4MnO₃/SrTiO₃ and YAlO₃ substrates. Nano-beam electron diffraction (NBED), structure factor calculation confirms that the crystal structure within both of the BFO thin films is rhombohedral by showing the rhombohedral signature Bragg’s reflections. X-ray reciprocal space mapping (XRSM) unambiguously consistent with NBED. Further investigation with atomic resolution scanning transmission electron microscopy (STEM) reveals that while the ~1.0% of the lattice mismatch found in the BFO 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 BFO grown on YAlO₃ 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.