Structural building-blocks of disordered Cu-Zr alloys

Abstract

The atomic structures of Cu-Zr alloys have been extensively studied due to the unusually high glass forming ability of this system. In this work, we investigate the nearest-neighbor atomic structures of several simulated disordered Cu-Zr compositions at three temperatures: 1450 K (liquid), 700 K (undercooled liquid), and 350 K (disordered solid). The results show that over 90 % of the local structures in these systems can be described by one of 12 “building-block” atomic cluster geometries, regardless of composition or temperature, and that these structures all exhibit icosahedral or quasi-icosahedral geometries. Most of the building-blocks are unique in their combination of representative Voronoi polyhedron geometry, predominant central atom type, and occupation probability for each site in the cluster. In addition to the 12 common building-blocks, 35 “outlier” structures unique to their simulated compositions and temperatures were observed. The outliers were primarily non-icosahedral. While the populations of the common building-blocks do not exhibit clear trends with temperature or composition, the overall population of outliers increased with decreasing temperature, suggestive of their role in accommodating the lack of translational order in the disordered solid.