Hidden topological order and its correlation with glass-forming ability in metallic glasses

Unlike the well-defined long-range periodic order that characterizes crystals, so far the inherent atomic packing mode in glassy solids remains mysterious. Based on molecular dynamics simulations, here we find medium-range atomic packing orders in metallic glasses, which are hidden in the diffraction data in terms of structure factors or pair correlation functions. The analysis of the hidden orders in various metallic glasses indicates that the glassy and crystalline solids share a nontrivial structural homology in short-to-medium range, and the hidden orders are formulated by inheriting partial crystalline orders during glass formation. As the number of chemical components increases, more hidden orders are often developed in a metallic glass and entangled topologically. We use this phenomenon to explain the geometric frustration in glass formation and the glass-forming ability of metallic alloys. Metallic glasses are amorphous in the absence of long-range atomic packing orders, but their medium-range order may not be completely lost. Here, Wu et al. identify a number of crystalline units that are entangled in medium range and their influence on the glass-forming ability in binary glasses.