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The slowest R to bypass crystallization to form glass is called the critical cooling rate, Rc, which characterizes how easily a system is to be vitrified. Glass-forming ability (GFA) is usually quantified by Rc and negatively correlated with it. GFA is a critical issue in the field of metallic glass (MG) (1–3) because it can be controlled over many orders of magnitude by a slight change of its composition or a small addition of a specific element. Thus, MG is the best system to study the physical mechanism of GFA. Among the known MGs, Rc can differ over 16 orders of magnitude (4–6).

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Because of the combination of amorphous structures and metallic bonds, MGs have shown many record-breaking properties that make themselves outstanding from traditional glasses and alloys (7, 8). Thus, they have been considered promising alternatives to conventional materials in various applications (9, 10). However, the achievable GFA primarily impedes this possibility. Despite the importance and high demand for the future development of desired MGs, the critical physical factor controlling GFA remains unclear. It is widely known that alloying is crucial for improving GFA. However, the underlying physical principles are mostly unknown. Thus, the fabrication of MGs largely relies on empirical rules. This problem is also crucial for phase-change materials (11–14), which are usually multicomponent mixtures of chalcogenides. For phase-change materials, the rapid switching speed is generally realized by poor GFA, opposite to MGs. To improve this situation, the physical understanding of the mechanism of the GFA is critical, both fundamentally and technologically.

Several empirical rules have been proposed either by treating MGs as hard sphere–like models aiming to maximize disordered packing capability (15–17) or by correlating GFA to various thermodynamic parameters that can be measured after obtaining the amorphous state (18–21). There is also an effort to estimate thermodynamic parameters from the high-temperature liquid (22). More recently, many geometrical structural descriptors from computer simulations have been used to describe the GFA of model MGs (23, 24). However, these phenomenological models do not have general validity. From the most fundamental viewpoint, glass formation is the consequence of the avoidance of crystallization (18, 25, 26). Unveiling the origin of the difference in crystallization kinetics of MGs should provide a physical basis to understand the factors controlling GFA.

A particularly vital question concerning multicomponent alloys, including MGs and phase-change materials, is the specificity of these systems. Similar alloying is possible for hard sphere–like systems such as colloids, but the variety of atoms with different characters and their combination for metallic alloys make the dimensions of the parameter space to explore high GFA vast. So, we require guiding physical principles to design useful materials with the desired GFA.

Here, we aim to unravel the fundamental physical mechanism of distinct GFAs of MGs by investigating their crystallization behaviors by molecular dynamics (MD) simulations. By studying the physical factors controlling crystal nucleation and growth, we find that (i) the most critical factor determining the crystallization rate is the liquid-crystal interface energy and (ii) the interface energy increases by the reduction of crystal-like preordering in a supercooled liquid state, which is caused by the nontrivial coupling between structural and compositional (or “chemical” in the MG terminology) orderings that create frustrations against crystallization. We also reveal that the structural and compositional differences across the liquid-crystal interface are of great significance not only in the crystal nucleation process but also in crystal growth. These findings suggest that the thermodynamic driving force, i.e., the chemical potential difference between the liquid and crystal phases, plays a minor role in determining GFA, contrary to the widespread belief

a later starburst galaxy NGC 253 (18), in the ultraluminous infrared galaxy Mrk273 (19), and in the AGNs of NGC 1068 and other active galaxies. The lower-energy isomer HCO+, on the other hand, is largely formed via protonation of CO by the ubiquitous ion H3+, and it is generally far more abundant. The relative abundance of HCO+ to HOC+ is seen to vary by many orders of magnitude, from well over 104 in the weakly irradiated PDR S140 (13) to 10 in the inner CND of Mrk273 (19). One question is, To what extent can HOC+ serve as a specific marker for XDRs (3)? A recent survey toward two quiescent cloud complexes of the galactic center, one of which is likely exposed to strong x-ray radiation, suggested that the CS:HOC+ ratio was a reliable marker for PDR/XDR components in galactic nuclei exposed to large-scale shocks, but there was no molecular tracer useful to distinguish PDR and XDR regions (20). For models to be used reliably to reveal conditions in distant molecular clouds in these very diverse environments, the yield of the associated reactions must be accurately known. These relative abundances obviously depend on the product branching ratios of the underlying chemical reactions that produce these molecules (13, 21). For the title reaction, the product channels are