Lee Junsu, Jeon Jieun, You Tae-Soo
Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Korea.
Materials (Basel). 2018 Mar 26;11(4):495. doi: 10.3390/ma11040495.
Four polar intermetallic compounds belonging to the ₂InLiGe₂ ( = La, Nd, Sm, Gd; = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system have been synthesized by the traditional solid-state reaction method, and their crystal structures have been characterized by single-crystal X-ray diffraction (SXRD) analyses. The isotypic crystal structures of four title compounds adopt the Mo₂FeB₂-type structure having the tetragonal space group ( = 2, Pearson code 40) with three crystallographically independent atomic sites and can be simply described as a pile of the identical 2-dimensioanl (2D) ₂InLiGe₂ slabs stacked along the -axis direction. The substituting Li atom shows a particular site preference for replacing In at the 2 site rather than Ge at the 4 in this crystal structure. As the size of a used rare-earth metal decreases from La to Gd throughout the title system, the Ge-Ge and Ge-In/Li bond distances, both of which consist of the 2D anionic Ge₂(In/Li) layer, gradually decrease resulting in the reduction of a unit cell volume. A series of theoretical investigations has been performed using a hypothetical structure model Gd₂InLiGe₂ by tight-binding linear muffin-tin orbital (TB-LMTO) method. The resultant densities of states (DOS) value at the Fermi level () suggests a metallic conductivity for this particular composition, and this calculation result is in a good agreement with the formal charge distribution assigning two extra valence electrons for a metal-metal bond in the conduction band. The thorough analyses of six crystal orbital Hamilton population (COHP) curves representing various interatomic interactions and an electron localization function (ELF) diagram indicating the locations of paired-electron densities are also provided in this article.
通过传统的固态反应法合成了属于₂InLiGe₂（ = La、Nd、Sm、Gd； = 0.13(1)、0.28(1)、0.43(1)、0.53(1)）体系的四种极性金属间化合物，并通过单晶X射线衍射（SXRD）分析对其晶体结构进行了表征。四种标题化合物的同型晶体结构采用具有四方空间群 （ = 2，皮尔逊编码40）的Mo₂FeB₂型结构，有三个晶体学独立的原子位点，可简单描述为沿 -轴方向堆叠的相同二维（2D）₂InLiGe₂板的堆积。在该晶体结构中，取代的Li原子在取代 2 位点的In时表现出特定的位点偏好，而不是取代 4 位点的Ge。在整个标题体系中，随着所用稀土金属的尺寸从La减小到Gd，构成二维阴离子Ge₂(In/Li)层的Ge-Ge和Ge-In/Li键长逐渐减小，导致晶胞体积减小。使用紧束缚线性 muffin-tin 轨道（TB-LMTO）方法对假设结构模型Gd₂InLiGe₂进行了一系列理论研究。费米能级（）处的态密度（DOS）计算结果表明该特定组成具有金属导电性，该计算结果与为导带中的金属-金属键分配两个额外价电子的形式电荷分布很好地吻合。本文还提供了代表各种原子间相互作用的六条晶体轨道哈密顿布居（COHP）曲线的详细分析以及表明成对电子密度位置的电子定域函数（ELF）图。
