Emergent electronic landscapes in a novel valence-ordered nickelate with tri-component nickel coordination

TL;DR

This paper reports the synthesis of a novel samarium nickelate with complex valence states and unique electronic landscapes, achieved through topochemical reduction, revealing new phases with exotic properties.

Contribution

It introduces a new valence-ordered nickelate with tri-component coordination, demonstrating the power of topochemical methods to create previously inaccessible materials.

Findings

Coexistence of multiple Ni valences and coordination geometries.

Emergence of intense orbital polarization and charge ordering.

Ground state characterized by strong electron localization.

Abstract

The metal-hydride-based topochemical reduction process has produced novel thermodynamically unstable phases across various transition metal oxide series with unusual crystal structures and non-trivial ground states. Here, by such an oxygen (de-) intercalation method we synthesis a novel samarium nickelate with ordered nickel valences associated with tri-component coordination configurations. This structure, with a formula of Sm$_{9}$Ni$_{9}$O$_{22}$ as revealed by four-dimensional scanning transmission electron microscopy, emerges from the intricate planes of {303}$_{\text{pc}}$ ordered apical oxygen vacancies. X-ray spectroscopy measurements and ab-initio calculations show the coexistence of square-planar, pyramidal and octahedral Ni sites with mono-, bi- and tri-valences. It leads to an intense orbital polarization, charge-ordering, and a ground state with a strong electron localization marked by the disappearance of ligand-hole configuration at low-temperature. This new nickelate compound provides another example of previously inaccessible materials enabled by topotactic transformations and presents a unique platform where mixed Ni valence can give rise to exotic phenomena.