Extraordinarily complex crystal structure with mesoscopic patterning in barium at high pressure
Extraordinarily complex crystal structure with mesoscopic patterning in barium at high pressure
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DOI：
10.1038/nmat3342
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发表时间：
2012-07-01
期刊：
影响因子：
41.2
通讯作者：
McMahon, M. I.
中科院分区：
文献类型：
--
作者：
Loa, I.;Nelmes, R. J.;McMahon, M. I.
元素钡采用一系列高压相，具有如此复杂的晶体结构，其中一些多年来一直无法确定结构。使用单晶同步辐射X射线衍射和新的数据分析策略，我们现在已经解决了这些晶体结构中最复杂的，即19 GPa下的Ba-IVc相。它是一个相当的主体-客体结构，在代表性单元中有768个原子，其中客体原子链的相对排列可以表示为一个二维图案，其中互锁的S形12链基序在一个方向上规则地重复，在另一个方向上以受约束的无序重复。在纳米尺度上存在这样的图案点在中程相互作用，这是不完全由这种金属中的巡回电子屏蔽。第一性原理电子结构计算的基础上，赝势理论和晶格周期性和原子间的距离的分析，我们合理化为什么Ba相的常见的密集堆积的晶体结构变得大力不利相比，复杂的结构Ba-IVc相，以及众所周知的压力诱导的s-d电子转移的作用是什么。
Elemental barium adopts a series of high-pressure phases with such complex crystal structures that some of them have eluded structure determination for many years. Using single-crystal synchrotron X-ray diffraction and new data analysis strategies, we have now solved the most complex of these crystal structures, that of phase Ba-IVc at 19 GPa. It is a commensurate host-guest structure with 768 atoms in the representative unit, where the relative alignment of the guest-atom chains can be represented as a two-dimensional pattern with interlocking S-shaped 12-chain motifs repeating regularly in one direction and repeating with constrained disorder in the other. The existence of such patterning on the nanometre scale points at medium-range interactions that are not fully screened by the itinerant electrons in this metal. On the basis of first-principles electronic structure calculations, pseudopotential theory and an analysis of the lattice periodicities and interatomic distances, we rationalize why the Ba phases with the common densely packed crystal structures become energetically unfavourable in comparison with the complex-structured Ba-IVc phase, and what the role of the well-known pressure-induced s-d electronic transfer is.