Electronic states of rutile dioxides: RuO2, IrO2, and RuxIr1−xO2

Abstract

We studied the metal $d$ and O $2p$-derived electronic states of Ru${\mathrm{O}}_2$, Ir${\mathrm{O}}_2$, ${\mathrm{Ru}}_{0.65}$ ${\mathrm{Ir}}_{0.35}$ ${\mathrm{O}}_2$, and ${\mathrm{Ru}}_{0.77}$ ${\mathrm{Ir}}_{0.23}$ ${\mathrm{O}}_2$ by photoemission spectroscopy with synchrotron radiation. Our data are in qualitative agreement with the Ru${\mathrm{O}}_2$ and Ir${\mathrm{O}}_2$ density-of-states curves calculated by Mattheis, which consist of one $d$-electron peak and three other major peaks with prevailing O $2p$ character. The quantitative agreement is reasonably good for Ru${\mathrm{O}}_2$, while discrepancies exist for the lower-energy states of Ir${\mathrm{O}}_2$. Revelation of these discrepancies, not evident from previous photoemission studies, was made possible by the investigation of mixed Ru${\mathrm{O}}_2$-Ir${\mathrm{O}}_2$ crystals.