Anomalous saturation of mixed valence in cerium-based systems as studied by x-ray absorption

The mixed valence of cerium-based metallic systems, as determined, for example, by x-ray-absorption experiments, never rises above 3.2-3.3 The $L_{\mathrm{III}}$ absorption-edge studies we report here show that this saturation effect occurs abruptly as a function of lattice constant (or composition) in the pseudobinary system $\mathrm{Ce}{\left({\mathrm{Pd}}_{1-x}{\mathrm{Rh}}_x\right)}_3$, in which it is possible to vary both continuously and rapidly the electronic properties. The saturation anomaly (at the valence 3.21) occurs at $x\approx 0.2$, the composition where anomalous saturation effects have been previously observed in the magnetic susceptibility, electronic specific heat, and electrical resistivity. The values of the latter quantities at $x\approx 0.2$ suggest a valency of ∼4, when interpreted within the promotional model.