Neutron diffraction and the structure of amorphous Ni0.95Tb0.05.

Abstract

Neutron diffraction measurements have been performed on amorphous Ni/sub 0.95/Tb/sub 0.05/ and crystalline Ni. Thick dc-sputtered films of the amorphous alloy were prepared by high-rate triode magnetron sputtering into liquid-nitrogen-cooled substrates. The contributions of structural and thermal disorder to the first-neighbor radial distribution function were obtained using the crystalline Ni results along with corrections for finite Q/sub max/. The results indicate a Ni-Ni first-neighbor structural disorder whose width, sigma/sub 1//r-bar/sub 1/approx. =3%, is substantially lower than values suggested for amorphous metals. Comparisons with theoretical models of the pair distribution function of a-Ni and a-Fe based on relaxed dense random-packed structures indicate good agreement with the results of Heimendahl. Density measurements have yielded the packing fraction for a-Ni/sub 0.95/Tb/sub 0.05/. Extrapolation of this value has allowed an estimate of the packing fraction of pure a-Ni to be obtained. The results indicate a density greater than the maximum for a hard-sphere, dense random-packing model, but significantly below that of crystalline values found in some relaxed models.