Actinide—noble-metal systems: An x-ray-photoelectron-spectroscopy study of thorium-platinum, uranium-platinum, and uranium-gold intermetallics

Abstract

A systematic study of the valence bands and selected core levels of polycrystalline samples of the intermetallic compounds ThPt, Th${\mathrm{Pt}}_2$, Th${\mathrm{Pt}}_3$, UPt, U${\mathrm{Pt}}_2$, U${\mathrm{Pt}}_3$, U${\mathrm{Pt}}_5$, U${\mathrm{Au}}_3$, and ${\mathrm{U}}_2$ ${\mathrm{Au}}_3$ has been performed by x-ray-photoelectron spectroscopy using Al $K \alpha$ radiation. The $5f$-electron states are found to be pinned to the Fermi energy in all uranium compounds suggesting a band description for these states. From the measured binding energies together with experimentally determined work functions a charge transfer from Th and U to the noble metals is concluded to take place. The highly asymmetric line shape of the U $4f$ core level is discussed and is found to be due to the high density of occupied and empty states near the Fermi energy. In the uranium-gold system the presence of a Kotani-Toyozawa satellite indicates the onset of a more localized $5f$-electron behavior. Magnetization measurements give support to the itinerant nature of the $5f$ electrons in the uranium-platinum compounds.