Moiré superlattice in relatively rotated and stacked BiMnO3 nanoflakes

Abstract

Moiré superlattices through twistronic architectures in 2D van der Waals materials are rapidly progressing. A similar architecture can be extended to ionic systems to explore their emerging functionalities. In this work, a moiré superlattice architecture is developed in BiMnO₃ nanoflakes, which are synthesised using the hydrothermal method. Their structure and morphology are confirmed through single-crystal electron diffraction (SAED) and diffraction contrast imaging (DCI). The as-synthesized sample is heat-treated to achieve a twist and stack architecture of superimposed nanoflakes. SAED, DCI, and high-resolution phase contrast imaging confirm the formation of a moiré superlattice in relatively rotated BiMnO₃ nanoflakes by a fixed angle of ∼7° around the [010] stacking axis. The moiré superlattice consists of nanodomains that share (200)_ms- and (002)_ms-type distorted interfaces. The experimentally measured lattice parameters of the moiré superlattice are a_ms ≈ 4.44 nm and c_ms ≈ 4.36 nm. This can be well correlated with the theoretically calculated lattice parameters. The strain distribution map of the moiré superlattice confirms the signature of a strain gradient. The arrangement of a locally distorted, relatively rotated group of orthorhombic and monoclinic orientational variants is shown. This study presents the first observation of the formation of a moiré superlattice in relatively rotated and superimposed BiMnO₃ nanoflakes. Such an architecture can be extended to perovskite and related oxide systems.