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

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 modi. cations 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.