Unravelling Local Atomic Order of the Anionic Sublattice in M(Al1-x Gax )4 with M=Sr and Ba by Using NMR Spectroscopy and Quantum Mechanical Modelling.
Unravelling Local Atomic Order of the Anionic Sublattice in M(Al1-x Gax )4 with M=Sr and Ba by Using NMR Spectroscopy and Quantum Mechanical Modelling.
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DOI：
10.1002/chem.201602475
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发表时间：
2016-12
期刊：
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通讯作者：
Oliver Pecher;Bernhard Mausolf;V. Peters;Kevin Lamberts;A. Korthaus;F. Haarmann
中科院分区：
文献类型：
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作者：
Oliver Pecher;Bernhard Mausolf;V. Peters;Kevin Lamberts;A. Korthaus;F. Haarmann
用x射线衍射（XRD）和差热分析对M=Sr和Ba的金属间相MAl4和MGa4的准二元截面进行了表征。两相完全混溶，形成M(Al1-x Gax)4与M=Sr和Ba的固溶体。这些结构以BaAl4结构类型结晶，其中四键和五键Al和/或Ga原子(分别表示为Al(4b), Al（5b), Ga（4b）和Ga(5b)）形成多阴离子Al/Ga亚晶格。应用固体27 Al核磁共振光谱分析和量子力学（QM）计算来研究Al中心的键合和Al/Ga取代的影响，特别是在低取代度的体系中。M(Al1-x Gax)4， M=Sr和Ba， 0.925≤x≤0.975，可以描述为二元多数化合物的矩阵，其中少量的Ga原子被Al原子取代。与QM计算结果一致的是，27个Al核磁共振和单晶XRD研究证明了Al（4b）在这些取代体系中的优先占位。此外，由于在聚阴离子亚晶格中除了孤立的Al（4b）原子外，还形成了Al(4b)-Al（4b）对，因此发现了两种不同的局部Al环境，即孤立的Al（4b1）原子和Al（4b2）原子。在周期边界条件下使用超晶格结构计算的电场梯度（EFG）的QM计算结果与核磁共振波谱结果吻合较好。
The quasibinary section of the intermetallic phases MAl4 and MGa4 with M=Sr and Ba have been characterised by means of X-ray diffraction (XRD) studies and differential thermal analysis. The binary phases show complete miscibility and form solid solutions M(Al1-x Gax )4 with M=Sr and Ba. These structures crystallise in the BaAl4 structure type with four- and five-bonded Al and/or Ga atoms (denoted as Al(4b), Al(5b), Ga(4b), and Ga(5b), respectively) that form a polyanionic Al/Ga sublattice. Solid state 27 Al NMR spectroscopic analysis and quantum mechanical (QM) calculations were applied to study the bonding of the Al centres and the influence of Al/Ga substitution, especially in the regimes with low degrees of substitution. M(Al1-x Gax )4 with M=Sr and Ba and 0.925≤x≤0.975 can be described as a matrix of the binary majority compound in which a low amount of the Ga atoms has been substituted by Al atoms. In good agreement with the QM calculations, 27 Al NMR investigations and single crystal XRD studies prove a preferred occupancy of Al(4b) for these substitution regimes. Furthermore, two different local Al environments were found, namely isolated Al(4b1) atoms and Al(4b2), due to the formation of Al(4b)-Al(4b) pairs besides isolated Al(4b) atoms within the polyanionic sublattice. QM calculations of the electric field gradient (EFG) using superlattice structures under periodic boundary conditions are in good agreement with the NMR spectroscopic results.