Topochemical Oxidation of Ruddlesden-Popper Nickelates Reveals Distinct Structural Family: Oxygen-Intercalated...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Condensed Matter Physics

Background:

• Layered perovskites, including Dion-Jacobson, Ruddlesden-Popper, and Aurivillius families, are known for diverse correlated electron phenomena like superconductivity and multiferroicity.
• Ruddlesden-Popper nickelates (La_n+1Ni_nO_3n+1+δ) are a key class of layered oxides with tunable electronic properties.
• Controlling oxygen stoichiometry and intercalation is crucial for modifying the properties of layered oxides.

Purpose of the Study:

• To synthesize and characterize a new family of layered perovskites via topochemical oxidation.
• To investigate the structural and electronic consequences of oxygen intercalation in Ruddlesden-Popper nickelates.
• To establish topochemical oxidation as a viable method for creating novel oxide phases.

Main Methods:

• Synthesis of La_n+1Ni_nO_3n+1+δ (n=1-4) Ruddlesden-Popper nickelate thin films.
• Post-growth topochemical oxidation using ozone annealing.
• Structural characterization using surface synchrotron X-ray diffraction and coherent Bragg rod analysis (COBRA).

Main Results:

• Successful intercalation of a significant amount of oxygen (δ ≈ 0.7-1.0) into the rock salt spacer layers, leading to a new class of layered perovskites.
• Observed substantial c-axis expansion (up to 17.8% for n=1) that decreases with increasing n.
• Demonstrated that oxygen intercalation induces metallicity, enhances Ni-O hybridization, and suppresses octahedral rotations.

Conclusions:

• Topochemical oxidation is a powerful strategy for accessing highly oxidized, metastable layered perovskite phases.
• The newly discovered oxygen-intercalated phases exhibit unique structural and electronic properties distinct from parent Ruddlesden-Popper and Aurivillius phases.
• This work opens new avenues for engineering electronic properties in layered oxides through intercalation chemistry, potentially leading to novel functional materials.