Static Displacements of Atoms in Crystalline Metallic Solid Solutions

Measurement of diffuse x-ray scattering from binary crystalline solid solutions at more than one x-ray energy is a sensitive probe of the average interatomic distance between neighboring pairs of atoms. Deviations of these bond distances by as little as 0.001Å are easily detected in the diffuse scattering from binary alloys consisting of atoms nearby in the periodic table and/or where x-ray energies chosen near their absorption edges can change the scattering contrast. Individual bond distances (AA, AB and BB) are recovered out to several near neighbor shells by combining three scattering measurements at x-ray energies chosen for maximum and minimum contrast. Average bond distances recovered from four metal alloys Fe77.5Ni22.5, Fe46.5Ni53.5Cr47Fe53and Cr20Ni80 are discussed. We find that the interatomic distances measured for these alloys give interesting insights to atomic displacements in solid solutions. Nearest neighbor bond distances are not well represented by phenomenological models based on pure element atomic size and concentration dependence of the lattice constants. Radial and nonradial displacements are recovered from these measurements of diffuse scattering.