Hybridization between4fand conduction electrons and saturation of mixed valence in cerium-based systems

The increase in 4f–conduction-electron hybridization, as determined from deep-core photoemission studies, is compared with the increase in the mixed valence across the archetypal, continuously valence-variable system Ce(${\mathrm{Pd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{T}}_{\mathrm{x}}$ ${)}_3$, where T=Ag or Rh. No anomaly is observed in the hybridization near $x_{\mathrm{Rh}=0.2\mathrm{}}$, where the mixed valence rather abruptly saturates. Instead, a linear relationship is found between the f-d hybridization and the volume of the unit cell. This finding is consistent with a recent model which explains the valence saturation in terms of thermodynamics.