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首页> 外文期刊>Crystal growth & design >Conflict between the Electronic Factors and Structure-Directing Rules in the lntergrowth Structure of Ca4Ag2+xGe4-x with x=1/2
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Conflict between the Electronic Factors and Structure-Directing Rules in the lntergrowth Structure of Ca4Ag2+xGe4-x with x=1/2

机译：x = 1/2的Ca4Ag2 + xGe4-x的共生结构中电子因子与结构导向规则之间的冲突

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Combined experimental and theoretical efforts to conceptually understand the structure directing forces in intergrowth structures have led to the discovery of the new ternary phase Ca4Ag2+xGe4-x (x = 0.5), obtained from high temperature reaction of the elements. It crystallizes in a new structure type according to single-crystal diffraction methods: monoclinic space group C2/m-i(10) with a = 10.7516(2) angstrom, b = 4.5475(1) angstrom, c = 18.7773(4)angstrom, beta = 93.69(2)degrees, V = 916.17(3) angstrom(3), Z = 4. The compound corresponds to the n = 2 member of the homologous series Ca2+nAg2+xGe2+n-x,that are built up by linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaAg1+xGe1-x (KHg2 or TiNiSi-type) structures, and may be partitioned in Ag-rich and Ag-free domains. Instead of the predicted Zr2CoSi2-type (C2/m-i(5)), a simultaneous doubling of the size of the two building blocks is observed with the dimerization of the (Ge-2) pairs into Ag-substituted tetramers (AgxGe4-x) due to valence electron shortage. However, the Ag/Ge mixing at one atomic site with roughly one-to-one atomic ratio is therefore unexplained. The electronic band structure calculations and analysis of the chemical bonding provided evidence that the Ag/Ge mixing is rather the result of a direct conflict between the Zintl-Klemm concept and empirically established "structure-directing rules". The implications of these findings for the poorly understood ordered staging structural interfaces, typically observed in secondary Li-ion batteries during charge/discharge process, are briefly discussed.
机译：结合实验和理论上的努力，从概念上理解了共生结构中的结构导向力，导致发现了新的三元相Ca4Ag2 + xGe4-x（x = 0.5），这是通过元素的高温反应获得的。根据单晶衍射方法，它以新的结构类型结晶：单斜晶空间群C2 / mi（10），其a = 10.7516（2）埃，b = 4.5475（1）埃，c = 18.7773（4）埃，β = 93.69（2）度，V = 916.17（3）埃（3），Z =4。该化合物对应于同源序列Ca2 + nAg2 + xGe2 + nx的n = 2个成员，它们由线性共生建立从CaGe（CrB型）和CaAg1 + xGe1-x（KHg2或TiNiSi型）结构切下的板坯，可以在富银和无银域中划分。代替了预测的Zr2CoSi2-型（C2 / mi（5）），随着（Ge-2）对二聚为Ag取代的四聚体（AgxGe4-x），观察到两个构件的尺寸同时加倍由于价电子短缺。然而，无法解释在一个原子位点处以大约一对一的原子比混合的Ag / Ge。电子能带结构的计算和化学键的分析提供了证据，表明Ag / Ge混合实际上是Zintl-Klemm概念与凭经验建立的“结构定向规则”之间直接冲突的结果。简要讨论了这些发现对于通常在二次锂离子电池充电/放电过程中观察不到的有序阶跃结构界面的理解。

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