Soft-Chemical Synthesis, Structure Evolution, and Insulator-to-Metal Transition in a Prototypical Metal Oxide, {\lambda}-RhO\(_2\)

• Published in: arXiv.org 2023-10
• Main Authors: Chamorro, Juan R, Zuo, Julia L, Bassey, Euan N, Watkins, Aurland K, Zhu, Guomin, Zohar, Arava, Wyckoff, Kira E, Kinnibrugh, Tiffany L, Lapidus, Saul H, Stemmer, Susanne, Clément, Raphaële J, Wilson, Stephen D, Seshadri, Ram
• Format: Article
• Language: English
• Subjects: Ammonium nitrate; Cerium ammonium nitrate; Chemical synthesis; Density functional theory; Distribution functions; Electron diffraction; Electronic structure; Function analysis; NMR; Nuclear magnetic resonance; Rhodium; Room temperature; Synchrotron radiation; Synchrotrons; Transition metal oxides; X ray powder diffraction
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2310.07053

\({\lambda}\)-RhO\(_2\), a prototype 4d transition metal oxide, has been prepared by oxidative delithiation of spinel LiRh\(_2\)O\(_4\) using ceric ammonium nitrate. Average-structure studies of this RhO\(_2\) polytype, including synchrotron powder X-ray diffraction and electron diffraction, indicate the room temperature structure to be tetragonal, in the space group I41/amd, with a first-order structural transition to cubic Fd-3m at T = 345 K on warming. Synchrotron X-ray pair distribution function analysis and \(^7\)Li solid state nuclear magnetic resonance measurements suggest that the room temperature structure displays local Rh-Rh bonding. The formation of these local dimers appears to be associated with a metal-to insulator transition with a non-magnetic ground state, as also supported by density functional theory-based electronic structure calculations. This contribution demonstrates the power of soft chemistry to kinetically stabilize a surprisingly simple binary oxide compound.