Polymorphism in the short-range order of Zr70Pd30 metallic glasses

We investigated the origin of the short-range order (SRO) of Zr-Pd based metallic glasses by different processing routes: melt spinning (MS) and mechanical milling (MM). The atomic pair distribution function (PDF) was observed using high energy synchrotron X-rays. Reverse Monte Carlo (RMC) simulations of the experimentally measured atomic pair distributions were performed to identify contrasting aspects of the partial pair distributions and differences in local chemical order between isochemical amorphous alloys prepared by these two very different synthesis techniques. The MS alloy is shown to have a SRO dominated by a random polyhedral configuration close to icosahedral symmetry. The MM samples have SRO to medium-range order (MRO) which is topologically similar to the MoSi2-type structure (I4/mmm), but chemically closer to the Al2Cu-type structure (I4/mcm).