$\mathrm{Ce}4f$ electron in Ce${\mathrm{H}}_{2.1}$, Ce${\mathrm{H}}_{2.4}$, Ce${\mathrm{Al}}_2$, Ce${\mathrm{Pd}}_3$, Ce${\mathrm{Rh}}_3$, and Ce${\mathrm{Ru}}_2$: A photoemission study using synchrotron radiation

We present a photoemission study of the $\mathrm{Ce}4f$ electron in materials which range from the localized, trivalent ($4f^1$) compounds Ce${\mathrm{H}}_2$ and Ce${\mathrm{Al}}_2$ to the reportedly tetravalent ($4f^0$) compounds Ce${\mathrm{Rh}}_3$ and Ce${\mathrm{Ru}}_2$. Using synchrotron radiation in the photon energy range of $10\le h\nu \le 140$ eV, we compare the valence-band emission of the Ce compounds with that of the analogous La compounds, paying particular attention to resonant behavior near the $4d\to 4f$ transition threshold. In addition, we use the partial photoelectron yield as an indicator of the degree of $4f$ localization as well as occupation. We find no evidence of a change in $4f$ occupation across the series Ce${\mathrm{H}}_{2.1}$→Ce${\mathrm{Ru}}_{2.}$ Instead, we find an increase in the width of the $4f$ emission and an increase in the effect of the $4f$ electron on the remaining band states. We conclude that the apparent valence changes in these particular compounds are due primarily to hybridization effects, in agreement with recent band-structure calculations.