Inherited structure of amorphous matter

Abstract

The inherent atomic packing mode of glassy solid is still one of the most interesting and fundamental problems in condensed-matter physics and material science. Although significant progress has been made and provided insights into the atomic-level structure and short-to-medium-range order in glass, the way of leading to the medium-range order is still unclear. Does a universal rule exist in nature to construct a glass structure as what has been discovered for crystals? Is there any connection between glassy and crystalline structures? If so, what does the connection look like and how is the connection related to the properties of the glassy solids? A glassy state is usually obtained through supercooling a liquid fast enough to avoid crystallization. The amorphous nature of glassy solid is experimentally ascertained by X-ray diffraction (XRD), transmission electron microscopy or selected area electron diffraction (SAED). Almost all kinds of glassy solids exhibit similar maze-like SAED patterns without any local lattice fringes and broad diffraction maximum characteristics in XRD data. However, the glassy solids are inherently different in atomic-level structure, demonstrated by their different response behaviors under certain conditions, for example, the diverse annealing-precipitated crystallinephases, the distinct mechanical strengths and ductilities, and the different thermal stabilities against crystallization. Unfortunately, such a difference in inherent structure among glassy solids cannot be easily differentiated from a trivial analysis of the experimental diffraction data. However, the diffraction data such as structure factors or pair correlation functions (PCFs) are not as trivial as they look like. On the contrary, some studies have demonstrated that plenty of structural information is hidden behind the data of structure factors or PCFs, for example, global packing containing both spherical-periodic order and local translational symmetry has been revealed by analyzing PCFs of many metallic glasses. A fractal nature of medium-range order in metallic glassis also found by examining the relationships between the first peak positions in structure factors and atomic molar volumes in many metallic glasses. In fact, the oscillation in the structure factor or PCF is an indication that a certain order does exist in amorphous solid. Therefore, a more careful scrutiny of the diffraction data is desired to gain a more in-depth insight into the glassy structure features and find a clue to unveil the natures of the inherent structures in different glasses. In this paper, we briefly review the recent molecular dynamics simulation results that the distinct hidden orders of atomic packing formula in medium range in these pure glassy solids are unveiled to be inherited from bcc order in glassy Fe and fcc order in glassy Ni, respectively, reflecting nontrivial structural homology between glassy and crystalline solids. By analyzing the partial PCFs of three two-component metallic glasses of CuZr, NiAl, and NiCu which are similar but have distinct glass-forming ability via MD simulations, very different hidden orders are observed in each individual system, indicating that the hidden orders are more complex in multicomponent metallic glasses. The different hidden orders in a multicomponent metallic glass may be entangled topologically. More different hidden orders lead to more complex topological entanglement. Further analysis indicates that the formation of the hidden orders during cooling and their topological entanglement produces the geometrical frustration against crystallization and is closely correlated with the glass-forming ability of metallic alloys. A “genetic map” of hidden orders in metallic glass is finally constructed, which provides new insights into the structural properties and structure-property relationships in metallic glass-forming liquids and glasses.