Revealing a high-density three-dimensional Ruddlesden–Popper-type fault network in an SmNiO₃ thin film

An epitaxial SmNiO₃ thin-film grown on an LaAlO₃ (001) substrate using pulsed laser deposition is investigated with spherical-aberration corrected scanning transmission electron microscopy techniques, including high-angle annular dark field, X-ray energy dispersive, and electron energy-loss spectroscopy. High-density Ruddlesden–Popper (RP)-type faults, which generate two types of image contrast due to overlaps along the electron beam direction, are identified with the translational vector of 1/2a⟨111⟩_c, corresponding to 1/2a⟨101⟩_c displacement of Sm atoms when observed along the [010]_c zone axis. These defects originate from Sm-rich non-stoichiometry within the SmNiO₃, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. The effects of high-density RP faults on the lattice strain, domain size, and strong electronic-lattice correlations indicate that RP faults can provide extra freedom to tailor the physical properties of SmNiO₃ thin films for potential electronic device applications. Graphic abstract: High-density Ruddlesden–Popper-type faults are revealed in an epitaxial SmNiO₃ thin film grown on LaAlO₃ (001) by pulsed laser deposition, originating from Sm-rich non-stoichiometry, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. RP faults provide extra freedom to tailor intriguing properties of SmNiO₃ for potential electronic device applications. [Figure not available: see fulltext.]