Arthur Williams

Laboratory x‐ray spectrometer for EXAFS and XANES measurements

An in‐lab x‐ray spectrometer is described which is capable of rapid acquisition of x‐ray absorption fine structure data for either extended x‐ray absorption fine structure measurements (EXAFS), or x‐ray absorption near edge structure studies (XANES). Intensities in excess of 107 photons/s in an ∼10 eV bandpass near 9 keV have been obtained using only a conventional sealed, fixed anode x‐ray tube operating at 1.5 kW. The spectrometer utilizes a focusing Johansson cut and bent single crystal as the monochromator and scans continuously from 8≲2θ≲160 degrees with only a single stepping motor driven movement. For 3d metal absorption edges, resolutions of ∼10eV are obtained in first order with a Ge(111) crystal and ∼1 eV in third order allowing in‐lab acquisition of both EXAFS and XANES data of synchrotron‐like quality.

The structure of some refractory transition metal-metalloid glasses☆

Abstract The radial distribution functions of four refractory alloys of composition (W0.5Ru0.5)0.8M0.2 where M = some metalloid from the group B, P, Al0.5B0.5, Si0.5B0.5 are presented along with densities, atomic volumes of metalloids and coordination numbers. The atomic distributions functions of these materials have been found to exhibit characteristics typical of many other amorphous metal-metalloid alloys. A comparison was made between the experimentally determined distribution functions for the WRu alloys and the Bernal Finney model calculations of dense random packings of hard spheres using the average WRu Gold-schmidt radii as the hard sphere radius. The agreement was found to be quite good in nearly all places, the most notable exception being in the vicinity of the second maxima, where the relative heights of the double peaks is found to be different from the DRPHS for the cases of M = B, P and B0.5Si0.5. In all cases for the WRu alloys the reduced radial distribution functions suggest a local short range order favoring common-base tetrahedra configurations as opposed to coplanar tetrahedra bases predominant in the DRPHS.

Partial pair correlation functions of La1−x(AlGaAu)x metallic glasses from x-ray diffraction data

Abstract X-ray diffraction studies of La1−xAlx, La1−x(Al0.5Ga0.5x, La1−xGax and La1−xAux metallic glasses have been performed for x = 0.20, 0.24 and 0.28. Similarities in the radial distribution functions for these materials as well as other data suggest that these alloys are isostructural. Experimental data from different alloys have therefore been used to separate the three different pair distribution functions, which are then compared to dense random packing models and data for other metallic glasses.

The structure and properties of some Rh0.92-xBxSi0.08 metallic glasses

Rhodium-based metallic glasses have been produced with over 40 at.% metalloids (Si and B). X-ray diffraction studies are presented here on Rh0.92-xBxSi0.08 metallic glasses, with x=0.22, 0.27 and 0.32, as well as mechanical, electrical and thermal analysis data. The structural studies suggest that this system undergoes a considerable change in short-range order with increasing boron concentration.