隐藏的多晶型物驱动B2O3中的玻璃化
Hidden polymorphs drive the vitrification in B2O3
摘要：
了解有利于液体结晶或玻璃化的条件一直是一个长期存在的科学问题。另一个相关的，但还没有很好地理解的问题是玻璃态和各种可能的结晶形式之间的关系，一个系统可能采取。在这种情况下，B2 O3是一个令人困惑的研究案例，因为i）它是最好的玻璃形成系统之一，尽管明显缺乏低压多晶型; ii）它在环境压力下以与唯一已知的结晶相异常不同的玻璃态形式玻璃化; iii）除非施加压力，否则它从不从熔体中结晶，这是一种称为结晶异常的有趣行为。在这里，通过从头计算，我们发现存在新的B2 O3晶体多晶型物的结构性质类似的玻璃和形成能量可比的已知的环境晶体。由此产生的构型简并性驱动系统在环境压力下玻璃化。简并度在压力下被提升，揭示了结晶异常的起源。这项工作调和的行为B2 O3与其他玻璃系统，并重申了系统的能力，玻璃化的多态性所发挥的作用。一些预测的晶体是完全由三重环组成的笼状材料，为硼基纳米多孔材料的合成开辟了新的前景。
英文摘要：
Understanding the conditions which favor crystallisation or vitrification of liquids has been a long-standing scientific problem. Another connected, and not yet well understood question is the relationship between the glassy and the various possible crystalline forms a system may adopt. In this context, B2O3 is a puzzling case of study since i) it is one of the best glass-forming systems despite an apparent lack of low-pressure polymorphism ii) it vitrifies in a glassy form abnormally different from the only known crystalline phase at ambient pressure iii) it never crystallises from the melt unless pressure is applied, an intriguing behaviour known as the crystallisation anomaly. Here, by means of ab-initio calculations, we discover the existence of novel B2O3 crystalline polymorphs with structural properties similar to the glass and formation energies comparable to the known ambient crystal. The resulting configurational degeneracy drives the system vitrification at ambient pressure. The degeneracy is lifted under pressure, unveiling the origin of the crystallisation anomaly. This work reconciles the behaviour of B2O3 with that from other glassy systems and reaffirms the role played by polymorphism in a system's ability to vitrify. Some of the predicted crystals are cage-like materials entirely made of three-fold rings, opening new perspectives for the synthesis of boron-based nanoporous materials.
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