Cationic Site-Preference in the YbCaAlSb (4.81 ≤ x ≤ 10.57) Series: Theoretical and Experimental Studies.

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.