Sa Hayeon, Lee Junsu, Jo Hongil, Moon Dohyun, Kim Min, Ok Kang Min, You Tae-Soo
Department of Chemistry and BK21Four Research Team, Chungbuk National University, Cheongju, Chungbuk 28644, Republic of Korea.
Department of Chemistry, Sogang University, Seoul 04107, Republic of Korea.
Inorg Chem. 2021 Jul 19;60(14):10124-10136. doi: 10.1021/acs.inorgchem.0c03705. Epub 2021 Jun 8.
Five ternary and quaternary Zintl phases in the solid-solution CaASbGe (A = Na, Li; 0.06(3) ≤ ≤ 0.17(5), 0.19(1) ≤ ≤ 0.55(1), 0.13(1) ≤ ≤ 0.22(1)) system have been successfully synthesized by both of the arc-melting and the molten Pb metal-flux reactions. The crystal structure of these title compounds was characterized by powder and single-crystal X-ray diffractions analyses, and all title compounds crystallized in the HoGe-type phase in the tetragonal space group 4/ ( = 4, Pearson code 84). The complex crystal structure can be described as an assembly of 1) three kinds of cationic polyhedra centered by three different Sb and 2) the cage-shaped anionic frameworks built through the connection of two types of Sb. The newly substituted -type double dopants of the cationic (Na and Li) and anionic (Ge) elements displayed particular site preferences, which were successfully explained by either the size-factor criterion based on the atomic size or the electronic-factor criterion based on the electronegativity of an element. Quite interestingly, as the reaction conditions were changed, the morphology shift of single crystals in CaNaSbGe occurred from a cubic-shaped to a hummocky-type, to a hopper-type, and eventually to an octahedral-shaped crystal, just like the Yakutian kimberlite diamonds. Moreover, we firmly believe that the inclusion of the -type Ge dopant for Sb was crucial to trigger this type of morphology shift and complete the octahedral-shaped morphology in the overall crystal-growth mechanism. The theoretical calculations using a DFT method rationalized the observed site preference of Na and the electronic effect of the -type Ge dopants. The Seebeck coefficient measurements for CaLiSbGe indicated that some portions of electron charge carriers were effectively eliminated by the -type double dopants using Li and Ge.
通过电弧熔炼和熔融铅金属助熔剂反应，成功合成了固溶体CaASbGe（A = Na，Li；0.06(3) ≤ ≤ 0.17(5)，0.19(1) ≤ ≤ 0.55(1)，0.13(1) ≤ ≤ 0.22(1)）体系中的五个三元和四元津特相。通过粉末和单晶X射线衍射分析对这些标题化合物的晶体结构进行了表征，所有标题化合物均在四方空间群4/（ = 4，皮尔逊编码84）中的HoGe型相中结晶。复杂的晶体结构可描述为1）以三种不同的Sb为中心的三种阳离子多面体和2）通过两种类型的Sb连接而成的笼状阴离子骨架的组合。阳离子（Na和Li）和阴离子（Ge）元素的新型取代型双掺杂剂表现出特定的位点偏好，这可以通过基于原子尺寸的尺寸因子标准或基于元素电负性的电子因子标准成功解释。非常有趣的是，随着反应条件的变化，CaNaSbGe单晶的形态从立方体形转变为小丘形，再到漏斗形，最终转变为八面体形晶体，就像雅库特金伯利岩钻石一样。此外，我们坚信，在整个晶体生长机制中，用Ge掺杂剂取代Sb对于引发这种形态转变并完成八面体形形态至关重要。使用密度泛函理论（DFT）方法进行的理论计算使观察到的Na的位点偏好和Ge掺杂剂的电子效应合理化。对CaLiSbGe的塞贝克系数测量表明，使用Li和Ge的双掺杂剂有效地消除了部分电子电荷载流子。
