ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxon, UK.
J Phys Condens Matter. 2011 Sep 14;23(36):365402. doi: 10.1088/0953-8984/23/36/365402. Epub 2011 Aug 25.
There has been a considerable debate about the nature of the short range atomic order in vitreous B(2)O(3). Some authorities state that it is not possible to build a model of glassy boron oxide of the correct density containing a large number of six-membered rings which also fits experimental diffraction data, but recent computer simulations appear to overrule that view. To discover which view is correct I use empirical potential structure refinement (EPSR) on existing neutron and x-ray diffraction data to build two models of vitreous B(2)O(3). One of these consists only of single boron and oxygen atoms arranged in a network to reproduce the diffraction data as closely as possible. This model has less than 10% of boron atoms in boroxol rings. The second model is made up of an equimolar mixture of B(3)O(3) hexagonal ring 'molecules' and BO(3) triangular molecules, with no free boron or oxygen atoms. This second model therefore has 75% of the boron atoms in boroxol rings. It is found that both models give closely similar diffraction patterns, suggesting that the diffraction data in this case are not sensitive to the number of boroxol rings present in the structure. This reinforces recent Raman, ab initio, and NMR claims that the percentage of boroxol rings in this material may be as high as 75%. The findings of this study probably explain why some interpretations based on different simulation techniques only find a small fraction of boroxol rings. The results also highlight the power of EPSR for the extraction of accurate atomistic representations of amorphous structures, provided adequate additional, non-scattering data (such as Raman and NMR in this case) are available.
关于非晶态 B(2)O(3) 的短程原子有序性的本质，存在着相当大的争议。一些权威人士声称，不可能构建一个具有正确密度且包含大量六元环的玻璃态硼氧化物模型，同时也符合实验衍射数据，但最近的计算机模拟似乎推翻了这一观点。为了确定哪种观点是正确的，我使用经验势结构精修（EPSR）对现有的中子和 X 射线衍射数据进行了分析，以构建两种非晶态 B(2)O(3)模型。其中一个模型仅由单硼和氧原子组成，这些原子以网络的形式排列，以尽可能精确地再现衍射数据。该模型中只有不到 10%的硼原子位于硼氧烷环中。第二个模型由等摩尔的 B(3)O(3)六元环“分子”和 BO(3)三角形分子组成，没有游离的硼或氧原子。因此，第二个模型中有 75%的硼原子位于硼氧烷环中。结果发现，这两种模型给出的衍射图案非常相似，这表明在这种情况下，衍射数据对结构中硼氧烷环的数量并不敏感。这进一步证实了最近的拉曼、从头算和 NMR 研究结果，即这种材料中硼氧烷环的比例可能高达 75%。本研究的结果可能解释了为什么基于不同模拟技术的一些解释仅发现硼氧烷环的一小部分。研究结果还突出了 EPSR 在提取非晶态结构的准确原子表示方面的强大功能，前提是可以获得足够的其他非散射数据（例如在这种情况下的拉曼和 NMR 数据）。
