Icosahedra clustering and short range order in Ni-Nb-Zr amorphous membranes

Abstract

Crystalline Pd/Pd-Ag membranes are widely used for hydrogen separation from CO2 and other gases in power generation applications. To substitute these high cost noble metal alloy membranes, the Ni-Nb-Zr amorphous alloys are being developed that exhibit relatively high permeability of hydrogen between 200–400 °C. Atom probe tomography (APT) experiments performed on these ribbons revealed nm-scale Nb-rich and Zr-rich regions (clusters) embedded in a ternary matrix, indicating phase separation within the Ni-Nb-Zr amorphous alloy. Density functional theory (DFT) simulations have predicted that these clusters are composed of icosahedral coordination polyhedra. The interatomic distances and correlation lengths of the short range order of these alloys were determined by neutron total scattering which match well with our DFT based molecular dynamics (DFT-MD) simulations.

Reflections on the Spatial Performance of Atom Probe Tomography in the Analysis of Atomic Neighborhoods

“…Its applicability to solute clustering or short-range ordering, that is, over interatomic distances, has not been assessed. Yet, a cornucopia of articles on bulk metallic glasses (Miller et al, 2003;Kontis et al, 2018;Sarker et al, 2018), nanocrystalline alloys (Detor et al, 2005), high-entropy alloys (Deng et al, 2015;Rao et al, 2017), and other compositionally complex alloys, as well as semiconductors (Galtrey et al, 2007) use it to assess an absence of solute clusters or short-range order.…”