Multiple-scattering effects in x-ray-absorption fine structure: Chromium in a tetrahedral configuration

Abstract

The contributions of the multiple-scattering processes in the extended x-ray-absorption fine structure (EXAFS) of tetrahedrally coordinated Cr in ${\mathrm{CrO}}_4$ and ${\mathrm{Cr}}_2$ ${\mathrm{O}}_7$ configurations have been investigated. The EXAFS measurements were carried out on crystalline and 0.5M aqueous solutions of ${\mathrm{K}}_2$ ${\mathrm{CrO}}_4$ and ${\mathrm{K}}_2$ ${\mathrm{Cr}}_2$ ${\mathrm{O}}_7$ compounds. It is shown that the contributions of the noncollinear multiple-scattering processes occurring in the first coordination shell is significant and these contributions must be included in the EXAFS analysis of the higher shells. The intensity of these contributions strongly depend upon the symmetry of the system. For a distorted tetrahedron, the intensity of the multiple-scattering contributions is less than that found in a regular tetrahedron. The feff code was used to model the contributions of the multiple-scattering processes. The theoretical calculations and the experimental results are in good agreement.