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Atomic-scale structural signature of dynamic heterogeneities in metallic liquids(金属液体中动态异质性的原子尺度结构特征)
发布时间:2017-10-13

Atomic-scale structural signature of dynamic heterogeneities in metallic liquids(金属液体中动态异质性的原子尺度结构特征) 
Alain Pasturel & Noel Jakse
npj Computational Materials 3:33 (2017)
doi:10.1038/s41524-017-0034-y
Published online:17 August 2017
Abstract| Full Text | PDF OPEN

摘要:液体如果具有足够高的冷却速度,将会越过其平衡熔融温度,并可在固化之前保持在亚稳、过冷状态。过冷液体的研究展示了几个有趣的动态现象,同时,由于液体结构和液体动力学之间存在明显的却又难以识别的联系,揭示与这些现象之间潜在的结构联系仍是一个重大挑战。第一性原理的从头算分子动力学(AIMD)模拟在原子尺度细节方面的描述是特别有效的方法,足以指导实验。基于把Cr加入Al基液体中的AIMD研究,我们首次证明:组分扩散的解耦与过冷状态下动态异质性之间存在紧密联系。此外,我们还证明了两种现象的起源都与结构异性(structural heterogeneity)相关,结构异性由化学短序列(CSRO)和局部五倍拓扑(ISRO)在液相短程之间的强相互作用引起,它在过冷时发展成以二十面体为主的中程序列(IMRO)。本研究结果表明,温度相关的金属-金属耦合分布函数中也观测到这种结构特征,从而为更详细的实验研究奠定了基础。   

Abstract: With sufficiently high cooling rates, liquids will cross their equilibrium melting temperatures and can be maintained in a metastable undercooled state before solidifying. Studies of undercooled liquids reveal several intriguing dynamic phenomena and because explicit connections between liquid structure and liquids dynamics are difficult to identify, it remains a major challenge to capture the underlying structural link to these phenomena. Ab initio molecular dynamics (AIMD) simulations are yet especially powerful in providing atomic-scale details otherwise not accessible in experiments. Through the AIMD-based study of Cr additions in Al-based liquids, we evidence for the first time a close relationship between the decoupling of component diffusion and the emergence of dynamic heterogeneities in the undercooling regime. In addition, we demonstrate that the origin of both phenomena is related to a structural heterogeneity caused by a strong interplay between chemical short-range order (CSRO) and local fivefold topology (ISRO) at the short-range scale in the liquid phase that develops into an icosahedral-based medium-range order (IMRO) upon undercooling. Finally, our findings reveal that this structural signature is also captured in the temperature dependence of partial pair-distribution functions which opens up the route to more elaborated experimental studies. 

Editorial Summary

Metallic liquids: Connection between liquid structure and liquid dynamics (金属液体:液体结构和液体动力学之间的连接) 

本研究基于计算模拟结果揭示了金属液体中原子尺度结构和动力学之间存在强烈联系。当液体材料快速冷却时,可避开结晶,形成亚稳态过冷状态。这样的系统表现出一系列有趣的动态现象,但是在实验上很难看到液体结构和液体动力学之间的相互作用。Grenoble Alpes大学的Alain Pasturel和Noel Jakse使用从头算分子动力学模拟表明,铬掺杂的铝基液体中,铬扩散与铝扩散有很强的去耦。这与动态异质性的出现密切相关,因为这两种效应都具有结构性的起源。他们的研究找到了液体结构和液体动力学之间的密切关系,并可能引起更进一步的实验研究。

Simulations show a strong connection between the atomic-scale structure and dynamics in metallic liquids. When a material is cooled rapidly it can avoid crystallization, forming a metastable undercooled state. Such systems exhibit a range of interesting dynamic phenomena but it is experimentally difficult to look at the interplay between the liquid structure and liquid dynamics. Using ab initio molecular dynamic simulations, Alain Pasturel and Noel Jakse from the University Grenoble Alpes show that in chromium-doped aluminum-based liquids there is a strong decoupling of the chromium diffusions from the aluminum diffusion. This is closely related to the emergence of dynamic heterogeneities, as both effects have a structural origin. These insights provide a close connection between structure and liquid dynamics and could lead to more elaborate experimental studies.

 

 
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