Nam Gnu, Jang Eunyoung, Jo Hongil, Han Mi-Kyung, Kim Sung-Jin, Ok Kang Min, You Tae-Soo
Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 28644, Korea.
Department of Chemistry, Chung-Ang University, Seoul 06974, Korea.
Materials (Basel). 2016 Jul 8;9(7):553. doi: 10.3390/ma9070553.
Four quaternary Zintl phases with mixed-cations in the YbCaAlSb (4.81 ≤ x ≤ 10.57) series have been synthesized by using the arc-melting and the Sn metal-flux reaction methods, and the isotypic crystal structures of the title compounds have been characterized by both powder and single-crystal X-ray diffraction (PXRD and SXRD) analyses. The overall crystal structure adopting the CaAlSb-type can be described as a pack of four different types of the spiral-shaped one-dimensional octahedra chains with various turning radii, each of which is formed by the distorted ((Yb/Ca)Sb₆) octahedra. Four symmetrically-independent cationic sites contain mixed occupations of Yb and Ca with different mixing ratios and display a particular site preference by two cationic elements. Two hypothetical structural models of Yb₄CaAlSb with different cationic arrangements were designed and exploited to study the details of site and bond energies. QVAL values provided the rationale for the observed site preference based on the electronegativity of each atom. Density of states (DOS) curves indicated a semiconducting property of the title compounds, and crystal orbital Hamilton population (COHP) plots explained individual chemical bonding between components. Thermal conductivity measurement was performed for YbCaAlSb, and the result was compared to compounds without mixed cations.
通过电弧熔炼和锡金属助熔剂反应法合成了YbCaAlSb（4.81≤x≤10.57）系列中具有混合阳离子的四种四元Zintl相，并通过粉末和单晶X射线衍射（PXRD和SXRD）分析对标题化合物的同型晶体结构进行了表征。采用CaAlSb型的整体晶体结构可描述为四种不同类型的具有不同回转半径的螺旋形一维八面体链的堆积，每条链由扭曲的((Yb/Ca)Sb₆)八面体形成。四个对称独立的阳离子位点包含Yb和Ca的混合占据，具有不同的混合比例，并显示出两种阳离子元素的特定位点偏好。设计并利用了两种具有不同阳离子排列的Yb₄CaAlSb假设结构模型来研究位点和键能的细节。QVAL值基于每个原子的电负性为观察到的位点偏好提供了理论依据。态密度（DOS）曲线表明标题化合物具有半导体性质，晶体轨道哈密顿布居（COHP）图解释了各组分之间的单个化学键。对YbCaAlSb进行了热导率测量，并将结果与不含混合阳离子的化合物进行了比较。
