SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions, The University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK.
Nat Mater. 2012 Jun 10;11(7):627-32. doi: 10.1038/nmat3342.
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.
钡元素呈现出一系列高压相，其晶体结构十分复杂，其中有一些多年来一直难以确定其结构。我们利用单晶同步加速器 X 射线衍射和新的数据解析策略，成功解析了这些晶体结构中最复杂的一种，即 19GPa 下的 Ba-IVc 相。该晶体结构为具有 768 个原子的同成分主-客体结构，其中客体原子链的相对排列可以用二维图案表示，沿一个方向周期性地重复交错的 S 型 12 链图案，而在另一个方向则受到约束的无序重复。这种纳米级图案的存在表明，在该金属中，巡游电子并未完全屏蔽长程相互作用。基于第一性原理电子结构计算、赝势理论以及晶格周期性和原子间距离的分析，我们解释了为什么具有常见密堆积晶体结构的 Ba 相在能量上不如复杂结构的 Ba-IVc 相有利，以及众所周知的压力诱导 s-d 电子转移的作用是什么。
