Fredrickson Rie T, Fredrickson Daniel C
Department of Chemistry, University of Wisconsin─Madison, 1101 University Avenue, Madison, Wisconsin53706, United States.
Inorg Chem. 2022 Nov 7;61(44):17682-17691. doi: 10.1021/acs.inorgchem.2c02785. Epub 2022 Oct 26.
The structures of complex intermetallic compounds can often be interpreted in terms of assemblies of units from simpler parent phases. For example, dodecagonal quasicrystals appear, when viewed down their high-symmetry axes, as plane-filling arrangements of square and triangular tiles corresponding to the CrSi and AlZr structure types, respectively. The atomic arrangements and cell-dimensions at the (100) faces of the cells of these structures provide a close geometrical match, which underlies not only dodecagonal quasicrystals and their approximants but also the much more common σ-phase structure. In this article, we show that such intergrowth of parent structures can arise from more than just geometrical coincidences but can be driven by a complementary matching of atomic packing forces. DFT-chemical pressure (CP) analysis on elemental versions of the CrSi and AlZr types reveal that in both cases arrays of positive interatomic pressures inhibit the formation of optimal contacts elsewhere in the structures. When they are lined up at the potential CrSi/AlZr interfaces, however, positive pressures from the two structures interdigitate rather than coincide, providing the opportunity for the relaxation of strained interatomic contacts. That such relief is afforded by the interfaces is confirmed by CP analysis of the σ-phase (FeCr-type) structure. Building on this scheme, we introduce the function to represent how the CP features of atoms within a structure impact planes or other surfaces that could serve as interfaces between different structures. Using this function, we then explore how the favorability of interfaces between CrSi- and AlZr-type units is tuned by partial elemental substitution with Si, as well as their potential matches with Laves phase units. The emerging picture provides an account for features of the quasicrystal approximants MnVSi and MnSi, as well as a framework for approaching intermetallic intergrowth structures more broadly.
复杂金属间化合物的结构通常可以用来自更简单母相的单元组装来解释。例如，当沿十二面体准晶体的高对称轴向下观察时，它们呈现为分别对应于CrSi和AlZr结构类型的正方形和三角形瓷砖的平面填充排列。这些结构晶胞（100）面的原子排列和晶胞尺寸提供了紧密的几何匹配，这不仅是十二面体准晶体及其近似晶体的基础，也是更为常见的σ相结构的基础。在本文中，我们表明，这种母结构的共生不仅可以源于几何巧合，还可以由原子堆积力的互补匹配驱动。对CrSi和AlZr类型的元素版本进行的密度泛函理论化学压力（CP）分析表明，在这两种情况下，正原子间压力阵列都会抑制结构中其他地方最优接触的形成。然而，当它们在潜在的CrSi/AlZr界面处排列时，来自两种结构的正压力相互交错而非重合，为缓解应变的原子间接触提供了机会。对σ相（FeCr型）结构的CP分析证实了这种缓解是由界面提供的。基于此方案，我们引入函数来表示结构内原子的CP特征如何影响平面或其他可作为不同结构之间界面的表面。利用这个函数，我们接着探究CrSi型和AlZr型单元之间界面的有利程度如何通过用Si进行部分元素替代来调节，以及它们与Laves相单元的潜在匹配情况。新出现的情况解释了准晶体近似物MnVSi和MnSi的特征，也为更广泛地研究金属间共生结构提供了一个框架。
