Effect of carbon content on electronic structure of uranium carbides

S. M. ButorinS. BautersL. AmidaniA. BeckA. RossbergS. WeissT. VitovaK. O. KvashninaO. Tougait

S. M. ButorinS. BautersL. Amidani ...+5 O. Tougait

Mar 2023

摘要

The electronic structure of UC$_x$ (x=0.9, 1.0, 1.1, 2.0) was studied bymeans of x-ray absorption spectroscopy (XAS) at the C $K$ edge and measurementsin the high energy resolution fluorescence detection (HERFD) mode at the U$M_4$ and $L_3$ edges. The full-relativistic density functional theorycalculations taking into account the $5f-5f$ Coulomb interaction $U$ andspin-orbit coupling (DFT+$U$+SOC) were also performed for UC and UC$_2$. Whilethe U $L_3$ HERFD-XAS spectra of the studied samples reveal little difference,the U $M_4$ HERFD-XAS spectra show certain sensitivity to the varying carboncontent in uranium carbides. The observed gradual changes in the U $M_4$ HERFDspectra suggest an increase in the C $2p$-U $5f$ charge transfer, which issupported by the orbital population analysis in the DFT+$U$+SOC calculations,indicating an increase in the U $5f$ occupancy in UC$_2$ as compared to that inUC. On the other hand, the density of states at the Fermi level were found tobe significantly lower in UC$_2$, thus affecting the thermodynamic properties.Both the x-ray spectroscopic data (in particular, the C $K$ XAS measurements)and results of the DFT+$U$+SOC indicate the importance of taking into account$U$ and SOC for the description of the electronic structure of actinidecarbides.

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