Jakse N, Pasturel A
Sciences et Ingénierie des Matériaux et Procédés, UMR CNRS 5266, Grenoble Université Alpes, BP 75, 38402 Saint-Martin d'Hères Cedex, France.
J Chem Phys. 2015 Aug 28;143(8):084508. doi: 10.1063/1.4929481.
We use ab initio molecular dynamics simulations to study the correlation between the local ordering and the dynamic properties of liquid Al80Ni20 alloy upon cooling. Our results evidence a huge increase of local icosahedral ordering (ISRO) in the undercooled regime which is more developed around Ni than Al atoms. We show that ISRO has a strong impact on self-diffusion coefficients of both species and is at the origin of their crossover from Arrhenius to non-Arrhenius behavior around a crossover temperature TX = 1000 K, located in the undercooled region. We also clearly identify that this temperature corresponds to the development of dynamic heterogeneities and to the breakdown of the Stokes-Einstein relation. At temperatures below this crossover, we find that the behavior of the diffusion and relaxation dynamics is mostly incompatible with predictions of the mode-coupling theory. Finally, an analysis of the van Hove function indicates that the crossover temperature TX marks the onset of a change in the diffusion mechanism from a normal flow to an activated process with hopping. From these results, the glass-forming ability of the alloy is discussed.
我们使用从头算分子动力学模拟来研究液态Al80Ni20合金在冷却过程中局部有序性与动力学性质之间的相关性。我们的结果表明，在过冷状态下，局部二十面体有序性（ISRO）大幅增加，且在Ni原子周围比在Al原子周围更为显著。我们表明，ISRO对两种原子的自扩散系数有强烈影响，并且是它们在位于过冷区域的交叉温度TX = 1000 K附近从阿仑尼乌斯行为转变为非阿仑尼乌斯行为的根源。我们还明确确定，该温度对应于动态非均匀性的发展以及斯托克斯-爱因斯坦关系的失效。在该交叉温度以下，我们发现扩散和弛豫动力学行为大多与模式耦合理论的预测不相符。最后，对范霍夫函数的分析表明，交叉温度TX标志着扩散机制从正常流动转变为具有跳跃的活化过程的开始。基于这些结果，我们讨论了该合金的玻璃形成能力。
