Short-to-medium range atomic order of Zr-Cu metallic glasses under compression

Metallic glasses are amorphous solids, usually alloys, with liquid-like atomic structure involving short-range order characterized by clusters of atoms and medium-range order - a spatial arrangement of those clusters. Amorphous metals lack the translational symmetry of crystals, yet their atomic packing density is nearly as high as in crystalline materials. The packing density of metallic glasses can be further enhanced by external pressure, which forces the disordered structure to accommodate the load. In this work, we employ molecular dynamics simulations to follow variations of short-to-medium-range order of three binary Zr-Cu metallic glasses during hydrostatic compression from 0 to 100 GPa. Our study confirms the previously reported unusual contraction of Zr-Zr pairs. We suggest that the effect is related to the theoretically predicted step change of the electronic configuration of Zr atoms under compression. A common feature of the investigated systems is an increasing contribution of icosahedral order around Cu atoms which is accomplished by preferential straining of the mechanically soft Zr-Zr bonds. Our results reveal structural similarities of different alloys in the high-pressure regime and show that their topological short-to-medium-range order becomes composition-independent under compression. We conclude that the topology of short-to-medium-range order in Zr-Cu MGs under compression exhibits a universal, composition-independent character.