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E-mail: tsyou@chungbuk.ac.krReceived August 22, 2013, Accepted September 5, 2013Key Words : Intermetallic compound, Crystal structure, Electronic structure, Site-preferenceZintl phases and polar intermetallics including lithiumatoms can offer not only a good opportunity to investigatethe correlation among crystal structure, chemical bonding,and physical properties given the unique role of lithiumacting as a “zwitter” ion

The new polar title compounds are prepared from the elements using molten In as a reactive flux (alumina or zirconia crucible, 960 °C, 20 h).

Four quaternary Zintl phases with mixed-cations in the Yb14-xCaxAlSb11 (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 Ca14AlSb11-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 Yb2+ and Ca2+ with different mixing ratios and display a particular site preference by two cationic elements. Two hypothetical structural models of Yb4Ca10AlSb11 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 Yb8.42(4)Ca5.58AlSb11, and the result was compared to compounds without mixed cations.

Five rare-earth metal containing quaternary phosphides in the RELixCu2–yP2 (RE = La, Pr, Nd, Gd, Er; 0.82 ≤ x ≤ 1; 1.19 ≤ y ≤ 1.54) series were synthesized by using high-temperature synthetic methods, and they were characterized by single-crystal X-ray diffraction. The title compounds crystallize in the trigonal space group Pm1 (Z = 1, Pearson code hP6) with four crystallographically independent atomic positions. The overall crystal structure can be described as a “Li-filled” CaAl2Si2-type structure, in which a partially occupied Li site is embedded within the “double-deck” layers formed by two anionic components. Tight-binding linear muffin-tin orbital calculations including density of states, crystal orbital Hamilton population, and electron localization function analyses provided rationales for the overall electronic structure and chemical bonding of the title phase. PrLi0.98(5)Cu1.54(1)P2 indicated an antiferromagnetic interaction of Pr at a relatively low temperature with a paramagnetic Curie temperature of –6.8 K and a thermal conductivity of 3.2 W mK–1 at 323 K.