X‐Ray Absorption Sensitivity at 5d Edges of High‐Valent Light Actinides to Crystal‐Field Strength and Covalency Effects

ABSTRACT The states were probed in and U(VI) and U(V) oxides using x‐ray absorption spectroscopy at the actinide edges. Measured data were analyzed by several approaches, including atomic, crystal‐field theory and the Anderson impurity model, to take into account the hybridization of actinide valence states with oxygen states. For Th(IV), the states are mainly affected by the crystal‐field interaction with the closest neighbors, as can be seen from the corresponding spectrum of . In turn, for U(VI) and U(V) oxides, the U –O charge transfer and high degree of covalency in the chemical bonding play a decisive role increasing the occupancy and consequently governing the ground and excited state properties. That is additionally illustrated by results from the calculations of the U x‐ray photoemission spectra for U(V) in the lattice of La‐doped .