Empty and filled valence-electron states of Lu–transition-metal compounds: An uv spectroscopy study

A joint uv-photoemission (hν=21.2 and 40.8 eV) and inverse-photoemission (hν=11–17 eV) spectroscopy investigation is reported on Lu and some Lu–transition-metal (M) compounds, namely ${\mathrm{LuCo}}_2$, ${\mathrm{LuRh}}_2$, and ${\mathrm{Lu}}_7$ ${\mathrm{Rh}}_3$ focused on the Lu and the M d-derived filled and empty electron states. The analysis is performed by considering the substitution effects of a 3d with a 4d M partner (${\mathrm{LuCo}}_2$ vs ${\mathrm{LuRh}}_2$) and by changing the stoichiometry and structure within the Lu-Rh phase diagram (${\mathrm{LuRh}}_2$ vs ${\mathrm{Lu}}_7$ ${\mathrm{Rh}}_3$ vs pure Lu). In ${\mathrm{LuRh}}_2$ the electron states, both below and above the Fermi level (${\mathit{E}}_{\mathit{F}}$), appear at lower energy (i.e., more bounded) as compared to ${\mathrm{LuCo}}_2$. ${\mathrm{Lu}}_7$ ${\mathrm{Rh}}_3$ shows a strong narrowing of the Rh d band below ${\mathit{E}}_{\mathit{F}}$, due to a strongly decreased Rh-Rh interaction whereas above ${\mathit{E}}_{\mathit{F}}$ a similarity with pure Lu at high-electron energies and a significant redistribution of the Rh 4d states are observed. A critical discussion of the results considering (i) the crystal structures and the atomic coordinations, and (ii) thermochemical estimations is performed. A comparison of the ${\mathrm{LuCo}}_2$ data with published theoretical results indicates that the d-derived empty electron states are appropriately described within a single-particle picture at variance with the d occupied states for which remarkable discrepancies between theory and experiment are found probably due to the larger radial extent and more pronounced delocalization of the antibonding empty states with respect to the filled states. Some general consequences of these effects will be discussed.