Advancing Heteroanionicity in Zintl Phases: Crystal Structures, Thermoelectric and Magnetic Properties of Two Quaternary Semiconducting Arsenide Oxides, Eu8Zn2As6O and Eu14Zn5As12O

Two novel quaternary oxyarsenides, Eu8Zn2As6O and Eu14Zn5As12O, were synthesized through metal flux reactions, and their crystal structures were established by single-crystal X-ray diffraction methods. Eu8Zn2As6O crystallizes in the orthorhombic space group Pbca, featuring polyanionic ribbons composed of corner-shared triangular [ZnAs3] units, running along the [100] direction. The structure of Eu14Zn5As12O crystallizes in the monoclinic space group P2/m and its anionic substructure can be described as an infinite "ribbonlike" chain comprised of [ZnAs3] trigonal-planar units, although the structural complexity here is greater and also amplified by disorder on multiple crystallographic positions. In both structures, the O2- anion occupies an octahedral void with six neighboring Eu2+ cations. Formal electron counting, electronic structure calculations, and transport properties reveal the charge-balanced semiconducting nature of these heteroanionic Zintl phases. High-temperature thermoelectric transport properties measurements on Eu14Zn5As12O reveal relatively high resistivity (ρ500K = 8 Ω·cm) and Seebeck coefficient values (S500K = 220 μV K-1), along with a low concentration and mobility of holes as the dominant charge-carriers (n500K = 8.0 × 1017 cm-3, μ500K = 6.4 cm2/V s). Magnetic studies indicate the presence of divalent Eu2+ species in Eu14Zn5As12O and complex magnetic ordering, with two transitions observed at T1 = 21.6 K and T2 = 9 K.

Yb14MgBi11: structure, thermoelectric properties and the effect of the structure on low lattice thermal conductivity

This paper presents a new compound Yb₁₄MgBi₁₁and its thermoelectric properties, especially its extremely low lattice thermal conductivity.

Optimizing the Dopant and Carrier Concentration of Ca5Al2Sb6 for High Thermoelectric Efficiency

The effects of doping on the transport properties of Ca₅Al₂Sb₆ are investigated using first-principles electronic structure methods and Boltzmann transport theory. The calculated results show that a maximum ZT value of 1.45 is achieved with an optimum carrier concentration at 1000 K. However, experimental studies have shown that the maximum ZT value is no more than 1 at 1000 K. By comparing the calculated Seebeck coefficient with experimental values, we find that the low dopant solubility in this material is not conductive to achieve the optimum carrier concentration, leading a smaller experimental value of the maximum ZT. Interestingly, the calculated dopant formation energies suggest that optimum carrier concentrations can be achieved when the dopants and Sb atoms have similar electronic configurations. Therefore, it might be possible to achieve a maximum ZT value of 1.45 at 1000 K with suitable dopants. These results provide a valuable theoretical guidance for the synthesis of high-performance bulk thermoelectric materials through dopants optimization.

Thermoelectric properties and electronic structure of the Zintl phase Sr₅In₂Sb₆ and the Ca(5-x)Sr(x)In₂Sb₆ solid solution

The Zintl phase Sr5In2Sb6 is isostructural with Ca5In2Sb6-a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for Sr5In2Sb6 reveal a decreased energy gap and decreased valence band effective mass relative to the Ca analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete Ca(5-x)Sr(x)In2Sb6 solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A5In2Sb6 compounds. Sr was shown to be fully miscible on the Ca site. The higher density of the Sr analog leads to a slight reduction in lattice thermal conductivity relative to Ca5In2Sb6, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds.