Topological and chemical ordering induced by Ni and Nd in Al87Ni7Nd6 metallic glass

The local atomic structure of Al87Ni7Nd6 amorphous metallic glass was determined by neutron diffraction and the pair density function (PDF) analysis. The local environments of the transition metal and rare earth ions were separately determined using Ni (58Ni and 60Ni) and Nd (142Nd and 144Nd) isotopes with very different neutron scattering lengths to separate their contributions. A distinct pre-peak was observed in reciprocal space indicative of clustering, a feature commonly present in good glass forming systems. The intensity of the pre-peak changes significantly with the substitution of Ni isotope but not so with Nd, suggesting that the transition metal is a major component to this peak. Such clustering might be a manifestation of chemical short-range ordering that is enhanced with Ni. The local environments for the Ni and Nd ions determined by the isotope difference PDF analysis are fundamentally distinct because Ni and Nd interact differently with Al giving rise to unique topologies. In particular for Ni, Ni-Al bond lengths are anomalously short due to stronger Ni-Al interactions and the local environment consists of distinct pair correlations. In contrast, the local Nd environment is more disordered with two separate Nd-Al environments and possibly relatively weaker interactions