Abstract
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.
Highlights
One of the smart ways to lower global energy consumption is to recover wasted heat produced by industries or automobiles and to convert it into electricity
During our systematic investigations to look for novel Zintl phase thermoelectric materials [16,17,18,19], we have successfully synthesized four quaternary compounds belonging to the Yb14-x Cax AlSb11 system
Four quaternary compounds in the Yb14-x Cax AlSb11 (4.81(3) ď x ď 10.57(2)) series have been synthesized by using the Sn metal-flux method, and four isotypic crystal structures were characterized by both powder and single-crystal X-ray diffraction (PXRD and SXRD) experiments
Summary
One of the smart ways to lower global energy consumption is to recover wasted heat produced by industries or automobiles and to convert it into electricity. Materials 2016, 9, 553 its figure of merit zT value even further, various cationic or anionic element substitutions have been attempted, respectively, to lower the lattice thermal conductivity or to optimize the carrier concentration [11,12,13,14,15]. During our systematic investigations to look for novel Zintl phase thermoelectric materials [16,17,18,19], we have successfully synthesized four quaternary compounds belonging to the Yb14-x Cax AlSb11 system. A series of theoretical calculations was performed by using the tight-binding linear muffin-tin orbital (TB-LMTO) method to understand the experimentally-observed cationic site preference, as well as the overall electronic structure. The temperature-dependent thermal conductivity was measured, and SEM images of nicely grown single crystals are provided, as well, in this article
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