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 Sm9Ni9O22 as revealed by four-dimensional scanning transmission electron microscopy, emerges from the intricate planes of {303}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.
@article{arxiv.2308.02855,
title = {Emergent electronic landscapes in a novel valence-ordered nickelate with tri-component nickel coordination},
author = {Aravind Raji and Zhengang Dong and Victor Porée and Alaska Subedi and Xiaoyan Li and Bernat Mundet and Lucia Varbaro and Claribel Domínguez and Marios Hadjimichael and Bohan Feng and Alessandro Nicolaou and Jean-Pascal Rueff and Danfeng Li and Alexandre Gloter},
journal= {arXiv preprint arXiv:2308.02855},
year = {2024}
}