Valence-Ordered Thin-Film Nickelate with Tri-component Nickel Coordination Prepared by Topochemical Reduction

In a groundbreaking study, researchers have synthesized Sm9Ni9O22 using the metal-hydride-based “topochemical reduction” process. This compound exhibits ordered nickel valences associated with tri-component coordination configurations, resulting in a unique crystal structure revealed through advanced microscopy techniques.

Through 4D-STEM, X-ray spectroscopy and theoretical calculations, the coexistence of square planar, pyramidal, and octahedral nickel sites with mono-, bi-, and tri-valences has been elucidated. This complex arrangement leads to intense orbital polarization and charge-ordering phenomena, with a distinct ground state marked by strong electron localization.

Sm9Ni9O22 represents an intriguing example of previously inaccessible materials enabled by topotactic transformations, offering potential applications in various technological domains and paving the way for further exploration in condensed matter physics.