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arXiv 1603.09115cond-mat.soft
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二元混合物中玻璃形成能力的成分依赖性:分层熵的作用

Composition dependence of the glass forming ability in binary mixtures: The role of demixing entropy

Ujjwal Kumar Nandi, Atreyee Banerjee, Suman Chakrabarty, Sarika Maitra Bhattacharyya

摘要:

我们提出了一个比较研究的玻璃形成能力的二元系统具有不同的组成,其中系统具有相似的全球晶体结构(CsCl+面心立方)。采用伞形取样技术的偏置蒙特卡罗模拟表明,随着较小粒子的组成减少,产生CsCl核的自由能成本增加。我们发现,具有相对较低的自由能成本,以形成氯化铯核的系统表现出更明显的液晶/晶体界面附近的预结晶分层。CsCl和fcc晶体之间的结构挫折需要这种分层。我们发现,接近等摩尔的混合物的熵罚分层较低,玻璃形成系统可以自发结晶时,接种一个核。这种熵罚作为组合物的函数显示出非单调行为,在类似于众所周知的Kob-Anderson(KA)模型的组合物处具有最大值。虽然KA模型显示了最大的熵罚,从而对CsCl形成的最大挫折,它也显示了强烈的倾向于结晶成fcc晶格的较大的“A”粒子,这可以解释从研究的能量。因此,对于更接近于等摩尔混合物的系统,尽管需要分层以提供其抗结晶的稳定性,但对于KA模型,其不是分层而是由较小的“B”颗粒周围的局部有利结构引起的缓慢动力学和结构挫折,这使其成为良好的玻璃形成剂。虽然这里研究的玻璃形成二元系统是非常相似的,不同的只是在组成,我们发现,他们的玻璃形成能力不能归因于一个单一的现象。

英文摘要:

We present a comparative study of the glass forming ability of binary systems with varying composition, where the systems have similar global crystalline structure (CsCl+fcc). Biased Monte Carlo simulations using umbrella sampling technique shows that the free energy cost to create a CsCl nucleus increases as the composition of the smaller particles are decreased. We find that the systems with comparatively lower free energy cost to form CsCl nucleus exhibit more pronounced pre-crystalline demixing near the liquid/crystal interface. The structural frustration between the CsCl and fcc crystal demands this demixing. We show that closer to the equimolar mixture the entropic penalty for demixing is lower and a glass forming system may crystallize spontaneously when seeded with a nucleus. This entropic penalty as a function of composition shows a non-monotonic behavior with a maximum at a composition similar to the well known Kob-Anderson (KA) model. Although the KA model shows the maximum entropic penalty and thus maximum frustration against CsCl formation, it also shows a strong tendency towards crystallization into fcc lattice of the larger "A" particles which can be explained from the study of the energetics. Thus for systems closer to the equimolar mixture although it is the requirement of demixing which provides their stability against crystallization, for KA model it is not demixing but slow dynamics and structural frustration caused by the locally favored structure around the smaller "B" particles which make it a good glass former. Although the glass forming binary systems studied here are quite similar, differing only in composition, we find that their glass forming ability cannot be attributed to a single phenomena.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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