Resolving the atomic structure of a new variant of bilayer nickelates with electron ptychography
ORAL
Abstract
The structure and superconducting properties of bilayer nickelates La3Ni2O7 (327) are highly sensitive to the growth and annealing conditions. Recently, the oxygen stoichiometry and atomic position in the 327 phase has been actively studied at atomic scale by transmission electron microscopy [1–3].
Here, we report the formation of La3Ni2(O, F)9 (329), a new variant of the 327 phase, and its structure determination by real-space imaging. Leveraging the depth resolution of multislice electron ptychography (MEP), we probe the intrinsic structure by differentiating the surface from bulk structure variations. Imaging the atomic structure in three dimensions using MEP reveals fully occupied interstitial sites at the rock salt layers within the 327 unit cell. Fluorine incorporation in the 329 phase leads to a substantially different nickel-anion bond lengths and angles compared to the 327 phase. Using both F- and O2- as dopants in La3Ni2(O, F)9 allows tuning of both charge and structure, providing a new platform for exploring superconductivity in nickelates.
Here, we report the formation of La3Ni2(O, F)9 (329), a new variant of the 327 phase, and its structure determination by real-space imaging. Leveraging the depth resolution of multislice electron ptychography (MEP), we probe the intrinsic structure by differentiating the surface from bulk structure variations. Imaging the atomic structure in three dimensions using MEP reveals fully occupied interstitial sites at the rock salt layers within the 327 unit cell. Fluorine incorporation in the 329 phase leads to a substantially different nickel-anion bond lengths and angles compared to the 327 phase. Using both F- and O2- as dopants in La3Ni2(O, F)9 allows tuning of both charge and structure, providing a new platform for exploring superconductivity in nickelates.
*This work made use of the Cornell Center for Materials Research shared instrumentation facility. H.Y. and D.A.M. acknowledge support by the NSF Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM) under cooperative agreement No. DMR-2039380.
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Publication: [1] Z. Dong et al., Visualization of oxygen vacancies and self-doped ligand holes in La3Ni2O7−δ, Nature 630, 847 (2024).
[2] Z. Dong et al., Interstitial oxygen order and its competition with superconductivity in La2PrNi2O7+δ, Nat. Mater. (2025).
[3] L. Bhatt et al., Resolving Structural Origins for Superconductivity in Strain-Engineered La3Ni2O7 Thin Films, arXiv:2501.08204 (2025).
Presenters
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Hongbin Yang
- Cornell University