We report measurements of x-ray-absorption near-edge structures (XANES) 20–100 eV above the ${\mathit{L}}_{\mathrm{III}}$ edge of Sm in mixed-valence SmS- and ${\mathrm{SmB}}_6$-based systems. We show that the XANES measurements are strongly dependent on temperature, hydrostatic pressure, and sample composition. A phenomenological model is developed to interpret the data, indicating the sensitivity of the spectra to any modification of the Sm valence, interatomic distances, or atomic relaxation. Atomic relaxation effects could be determined for a large number of compounds. We discuss the static or dynamic nature of the valence mixing from the importance of atomic relaxation effects deduced from our data. Possible complications arising from final-state effects and their influence on our interpretations are addressed.

• Received 14 September 1989

DOI:https://doi.org/10.1103/PhysRevB.41.6768