arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1607.04794cond-mat.mtrl-sci
收藏

冰VI到冰XV氢序相变的详细晶体学分析

Detailed crystallographic analysis of the ice VI to ice XV hydrogen ordering phase transition

Christoph G. Salzmann, Ben Slater, Paolo G. Radaelli, John L. Finney, Jacob J. Shephard, Martin Rosillo-Lopez, James Hindley

摘要:

用中子衍射方法详细研究了常压下D2 O冰VI到冰XV氢有序相变。晶格常数被发现是氢有序的敏感指标。a和b晶格常数的合同,而一个显着的膨胀,在c被发现后氢排序。总的来说,氢有序化转变伴随着体积的小幅增加,这解释了为什么在压力下冷却时更难以观察到相变。在1.4GPa下缓慢冷却的冰VI得到基本上完全氢无序的冰VI。与早期的研究一致,在环境压力下缓慢冷却后获得的冰XV最好用P-1空间群对称性描述。使用一种新的计算方法,我们实现了原子重建的超胞结构,这是一致的平均部分有序结构来自Rietveld细化。这表明C型网络在冰XV中最普遍,但也确定了完全氢有序网络分类之外的其他结构基序。最近提出的Pmmn冰XV结构模型被发现与我们的衍射数据是不相容的,我们认为,只有能够描述完整的氢顺序的结构模型应该被使用。

英文摘要:

The D2O ice VI to ice XV hydrogen ordering phase transition at ambient pressure is investigated in detail with neutron diffraction. The lattice constants are found to be sensitive indicators for hydrogen ordering. The a and b lattice constants contract whereas a pronounced expansion in c is found upon hydrogen ordering. Overall, the hydrogen ordering transition goes along with a small increase in volume which explains why the phase transition is more difficult to observe upon cooling under pressure. Slow-cooling ice VI at 1.4 GPa gives essentially fully hydrogen-disordered ice VI. Consistent with earlier studies, the ice XV obtained after slow-cooling at ambient pressure is best described with P-1 space group symmetry. Using a new computational approach, we achieve the atomistic reconstruction of a supercell structure that is consistent with the average partially ordered structure derived from Rietveld refinements. This shows that C-type networks are most prevalent in ice XV but other structural motifs outside of the classifications of the fully hydrogen-ordered networks are identified as well. The recently proposed Pmmn structural model for ice XV is found to be incompatible with our diffraction data and we argue that only structural models that are capable of describing full hydrogen order should be used.

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。

↑