Full icosahedra dominate local order in Cu64Zr34 metallic glass and supercooled liquid

Extensive molecular dynamics simulations were carried out to monitor the development of icosahedral order in Cu64Zr34 liquid and metallic glass (MG). This study illustrates that at this Cu-rich Cu-Zr alloy composition, Cu-centered full icosahedra constitute the dominant and characteristic short-range-ordered coordination motif. The results for this model liquid/glass address five questions regarding the ordering of Cu-centered coordination polyhedral towards full icosahedra, including: (i) its evolution and extent during prolonged structural relaxation; (ii) the resulting reduction in potential energy and slowing-down of dynamics; (iii) the accompanying preference of a particular type of Zr-centered Kasper coordination polyhedra; (iv) the evolution and conversion of polyhedral connection schemes in the medium range; and (v) the formation and percolation of networks formed by interpenetrating connection of icosahedra to constitute a stiff backbone over extended range. Five related issues are also clarified, to: (i) differentiate full-icosahedra-based ordering from the generally favorable fivefold bonds; (ii) compare the Cu-based perspective with a Zr-centric view; (iii) systematically list the rationales behind focusing on icosahedral order for explaining the Cu64Zr34 MG/liquid properties; (iv) discuss other non-icosahedral ordering varieties; and (v) comment on the most liquid-like local environments. Taken together, the ten issues addressed set the stage for understanding structure-property relations in a category of amorphous alloys that can be characterized based on full-icosahedral ordering.