Visualization of oxygen vacancies and self-doped ligand holes in La3Ni2O7−δ

Zehao Dong, Mengwu Huo, Jie Li, Jingyuan Li, Pengcheng Li, Hualei Sun, Lin Gu, Yi Lu (), Meng Wang (), Yayu Wang () and Zhen Chen ()
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Zehao Dong: Tsinghua University
Mengwu Huo: Sun Yat-Sen University
Jie Li: Nanjing University
Jingyuan Li: Sun Yat-Sen University
Pengcheng Li: Tsinghua University
Hualei Sun: Sun Yat-Sen University
Lin Gu: Tsinghua University
Yi Lu: Nanjing University
Meng Wang: Sun Yat-Sen University
Yayu Wang: Tsinghua University
Zhen Chen: Chinese Academy of Sciences

Nature, 2024, vol. 630, issue 8018, 847-852

Abstract: Abstract The recent discovery of superconductivity in La3Ni2O7−δ under high pressure with a transition temperature around 80 K (ref. 1) has sparked extensive experimental2–6 and theoretical efforts7–12. Several key questions regarding the pairing mechanism remain to be answered, such as the most relevant atomic orbitals and the role of atomic deficiencies. Here we develop a new, energy-filtered, multislice electron ptychography technique, assisted by electron energy-loss spectroscopy, to address these critical issues. Oxygen vacancies are directly visualized and are found to primarily occupy the inner apical sites, which have been proposed to be crucial to superconductivity13,14. We precisely determine the nanoscale stoichiometry and its correlation to the oxygen K-edge spectra, which reveals a significant inhomogeneity in the oxygen content and electronic structure within the sample. The spectroscopic results also reveal that stoichiometric La3Ni2O7 has strong charge-transfer characteristics, with holes that are self-doped from Ni sites into O sites. The ligand holes mainly reside on the inner apical O and the planar O, whereas the density on the outer apical O is negligible. As the concentration of O vacancies increases, ligand holes on both sites are simultaneously annihilated. These observations will assist in further development and understanding of superconducting nickelate materials. Our imaging technique for quantifying atomic deficiencies can also be widely applied in materials science and condensed-matter physics.

Date: 2024
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DOI: 10.1038/s41586-024-07482-1

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