Orientation and temperature dependence of the Cd K-shell EXAFS of polycrystalline and single-crystal Cd metal

The Cd K-shell X-ray absorption spectrum (26.6 to 27.6 keV) of polycrystalline Cd metal has been recorded at temperatures from 20 to 300 K. The spectrum of a Cd single crystal was also measured at temperatures from 4 to 300 K with the crystal in two orientations-one optimising the EXAFS from the first Cd distance (2.97 AA), the other optimising the EXAFS from the second Cd distance (3.29 AA). The visibility of the second Cd-Cd distance varies greatly in the spectra on account of the large anisotropy in the thermal motion. The approximate Debye-Waller factors for the thermal motion along the two near-neighbour directions are derived in a harmonic approximation and compared to other measures of the relative thermal motion.