Artigo Acesso aberto

Oxidation and aging in U and Pu probed by spin-orbit sum rule analysis: Indications for covalent metal-oxide bonds

2006; American Physical Society; Volume: 73; Issue: 3 Linguagem: Inglês

10.1103/physrevb.73.033109

ISSN

1550-235X

Autores

K. T. Moore, G. van der Laan, R.G. Haire, M. A. Wall, A. J. Schwartz,

Tópico(s)

Nuclear Materials and Properties

Resumo

Transmission electron microscopy is used to acquire electron energy-loss spectra from phase-specific regions of Pu and U metal, $\mathrm{Pu}{\mathrm{O}}_{2}$ and $\mathrm{U}{\mathrm{O}}_{2}$, and aged, self-irradiated Pu metal. The ${N}_{4,5}$ $(4d\ensuremath{\rightarrow}5f)$ spectra are analyzed using the spin-orbit sum rule. Our results show that the technique is sensitive enough to detect changes in the branching ratio of the white-line peaks between the metal and dioxide of both U and Pu. There is a small change in the branching ratio between different Pu metals, and the data trends as would be expected for varying $f$ electron localization, i.e., $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$, $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$, and aged $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$. Moreover, our results suggest that the metal-oxide bonds in $\mathrm{U}{\mathrm{O}}_{2}$ and $\mathrm{Pu}{\mathrm{O}}_{2}$ are strongly covalent in nature and do not exhibit an integer valence change as would be expected from purely ionic bonding.

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