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首页> 外文期刊>Physical review >First-principles study of a sodium borosilicate glass-former. Ⅰ. The liquid state
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First-principles study of a sodium borosilicate glass-former. Ⅰ. The liquid state

机译：硼硅酸钠玻璃形成剂的第一性原理研究。 Ⅰ。液态

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We use ab initio simulations to study the static and dynamic properties of a sodium borosilicate liquid with composition 3Na_2O-B_2O_3-6SiO_2, i.e., a system that is the basis of many glass-forming materials. In particular, we focus on the question how boron is embedded into the local structure of the silicate network liquid. From the partial structure factors we conclude that there is a weak nanoscale phase separation between silicon and boron and that the sodium atoms form channel-like structures as they have been found in previous studies of sodosilicate glass-formers. Our results for the x-ray and neutron structure factor show that this feature is basically not detectable in the former but should be visible in the latter as a small peak at small wave vectors. At high temperatures we find a high concentration of threefold coordinated boron atoms which decreases rapidly with decreasing T, whereas the number of fourfold coordinated boron atoms increases. Therefore, we conclude that at the experimental glass transition temperature most boron atoms will be fourfold coordinated. We show that the transformation of B into B with decreasing T is not just related to the diminution of nonbridging oxygen atoms as claimed in previous studies, but to a restructuring of the silicate matrix. The diffusion constants of the various elements show an Arrhenius behavior and we find that the one for boron has the same value as the one of oxygen and is significantly larger than the one of silicon. This shows that these two network-formers have rather different dynamical properties, a result that is also confirmed from the time dependence of the van Hove functions. Finally, we show that the coherent intermediate scattering function for the sodium atoms is very different from the incoherent one and that it tracks the one of the matrix atoms.
机译：我们使用从头开始的模拟方法来研究组成为3Na_2O-B_2O_3-6SiO_2的硼硅酸钠液体的静态和动态特性，该系统是许多玻璃形成材料的基础。特别地，我们关注于硼如何嵌入硅酸盐网络液体的局部结构中的问题。根据部分结构因素，我们得出结论，硅和硼之间存在较弱的纳米级相分离，并且钠原子形成通道状结构，正如先前在钠硅酸盐玻璃形成剂的研究中所发现的那样。我们对X射线和中子结构因子的研究结果表明，该特征基本上在前者中是无法检测到的，但在后者中应以小波矢处的一个小峰可见。在高温下，我们发现高浓度的三重配位硼原子随着T的降低而迅速降低，而四重配位硼原子的数量却增加。因此，我们得出结论，在实验玻璃化转变温度下，大多数硼原子将被四重配位。我们表明，随着T值的降低，B转变为B不仅与先前研究中所声称的非桥接氧原子的减少有关，而且与硅酸盐基质的重组有关。各种元素的扩散常数显示出Arrhenius行为，我们发现硼的一种元素与氧的一种元素具有相同的值，并且明显大于硅的一种。这表明这两个网络形成者具有相当不同的动力学特性，这一结果也从van Hove函数的时间依赖性得到了证实。最后，我们表明钠原子的相干中间散射函数与非相干中间散射函数非常不同，并且它跟踪基质原子之一。

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