[10a-PA3-1~10] 6.1 強誘電体薄膜

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

〇永沼 博⁵、In-Tae Bae^1,2、安井 伸太郎³、伊藤 満³、白石 貴久⁴、木口 賢紀⁴、一ノ瀬 智浩⁵ (1.ニューヨーク州立大学S3IP、2.ニューヨーク州立大学、3.東工大フロンティア、4.東北大金研、5.東北大工)

キーワード：マルチフェロイックス、構造解析、透過型電子顕微鏡

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.