Templating Structural Progessions in Intermetallics: How Chemical Pressure Directs Helix Formation in the Nowotny Chimney Ladders
Templating Structural Progessions in Intermetallics: How Chemical Pressure Directs Helix Formation in the Nowotny Chimney Ladders
复制标题
金属间化合物的模板化结构进展：化学压力如何引导诺沃特尼烟囱梯中的螺旋形成
DOI：
10.1021/acs.inorgchem.9b00132
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发表时间：
2019
影响因子：
4.6
通讯作者：
Fredrickson, Daniel C.
中科院分区：
文献类型：
--
作者：
Lu, Erdong;Fredrickson, Daniel C.
在金属间相的结构多样性中，可以感知到将复杂结构与相对简单的母体结构相关联的层次结构。一个例子是诺沃特尼烟囱梯（NCL）系列，一个过渡金属主族（T-E）化合物家族，其中T亚晶格描绘出由E原子螺旋填充的螺旋通道。一系列的结构出现从这种安排，因为间距沿着通道的E原子平滑地变化相对于T框架，主要是由优化的价电子浓度。在这篇文章中，我们展示了如何通过NCL的密度泛函理论-化学压力（DFT-CP）方案来预测和解释这种行为。RuGa 2母结构的CP分析揭示了Ga原子上的CP四极（软原子运动的迹象），其产生于沿沿着一个轴的过短Ru-Ga接触和垂直方向上未充分利用的空间。在它们的位置和取向中，CP四极杆突出了Ga原子的容易运动的螺旋路径，其避免了已经应变的Ru-Ga接触的进一步压缩。发现一系列NCL的E原子（在其DFT优化的几何结构中）都位于沿着该螺旋，CP四极特征是一个持久的特征。通过这种方式，NCL共有的T亚晶格编码了螺旋路径，通过该螺旋路径可以改变E原子间距，从而创建了一种机制来适应电子驱动的成分变化。这些结果说明了CP方案如何与电子计数规则相结合，以创建定义明确的结构序列，潜在地指导新的金属间相的发现。
In the structural diversity of intermetallic phases, hierarchies can be perceived relating complex structures to relatively simple parent structures. One example is the Nowotny Chimney Ladder (NCL) series, a family of transition metal–main group (T–E) compounds in which the T sublattices trace out helical channels populated by E-atom helices. A sequence of structures emerges from this arrangement because the spacing along the channels of the E atoms smoothly varies relative to that of the T framework, dictated largely by optimization of the valence-electron concentration. In this Communication, we show how this behavior is anticipated and explained by the Density Functional Theory-Chemical Pressure (DFT-CP) schemes of the NCLs. A CP analysis of the RuGa2parent structure reveals CP quadrupoles on the Ga atoms (telltale signs of soft atomic motion) that arise from overly short Ru–Ga contacts along one axis and underutilized spaces in the perpendicular directions. In their placement and orientation, the CP quadrupoles highlight a helical path of facile movement for the Ga atoms that avoids further compression of the already strained Ru–Ga contacts. The E atoms of a series of NCLs (in their DFT-optimized geometries) are all found to lie along this helix, with the CP quadrupole character being a persistent feature. In this way, the T sublattice common to the NCLs encodes helical paths by which the E-atom spacing can be varied, creating a mechanism to accommodate electronically driven compositional changes. These results illustrate how CP schemes can be combined with electron-counting rules to create well-defined structural sequences, potentially guiding the discovery of new intermetallic phases.