Near-edge and EXAFS studies of amorphous palladium-germanium

Abstract

High-resolution gamma -ray absorption spectra measured on the germanium K edge in amorphous and crystalline Pd-Ge alloys of composition Pd80Ge20 are reported. The spectra exhibit well resolved near-edge structures (XANES) with significant differences between the amorphous and crystalline samples. At energies >40 eV above the edge, EXAFS data from the two specimens are almost identical, indicating a similar nearest-neighbour environment for the Ge atoms in the two materials. Calculations of the near-edge structure, made using a full multiple scattering theory for clusters of atoms which model possible local structures about the Ge in the amorphous system, reproduce all the major features in the experimental spectrum. These calculations demonstrate that XANES is sensitive to the local symmetry at the absorbing site and to second- and higher-order coordination shells. XANES thus provides structural information additional to that available from EXAFS, which is normally found to be sensitive only to nearest-neighbour distances and coordination numbers in amorphous materials.