Electron-energy-loss spectroscopy and X-ray absorption spectroscopy as complementary probes for complex f-electron metals: cerium and plutonium

Abstract

In this paper, we demonstrate the power of electron-energy-loss spectroscopy (EELS) in a transmission electron microscope by investigating the electron structure of two f-electron metals: Ce and Pu. It is shown that EELS in a transmission electron microscope may be used to circumvent the difficulty of producing single-phase or single-crystal samples owing to its high spatial resolution, and that diffraction patterns and images can be acquired, providing unambiguous phase determination when acquiring spectra. EELS results are supported by synchrotron-radiation-based X-ray absorption, multielectron atomic spectral simulations, and local density approximation calculations based on density-functional theory with the generalized gradient approximation. For Ce, it is shown that changes in {111} stacking sequences can drive substantial modifications in the electronic structure of close-packed phases of Ce that have similar atomic volumes, contrary to previous assumptions in literature. For Pu, it is shown that Russell–Saunders (L–S) coupling fails for the 5f states and that either a j–j or an intermediate scheme must be used for the actinides because of the considerable spin–orbit interaction in the 5f states. We present a model showing how the 5f states behave along the light actinide series.

Acknowledgements

This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-Eng-48, with support from Lawrence Berkeley National Laboratory (contract DE-AC03-76SF00098). The Advanced Light Source and the Spectromicroscopy Facility (beam line 7.0) have been built and operated under funding from the Office of Basic Energy Science at the US Department of Energy. The authors wish to thank Gil Gallegos for the Ce samples, Jason Lashley and Michael Blau for the Pu samples, and R. Schultz, D. Shuh, J. Terry, J.D. Farr, T. Zocco, K. Heinzelman and E. Rotenberg for help with the Pu data collection at the Advanced Light Source.