Advancing Heteroanionicity in Zintl Phases: Crystal Structures, Thermoelectric and Magnetic Properties of Two Quaternary Semiconducting Arsenide Oxides, Eu 8 Zn 2 As 6 O and Eu 14 Zn 5 As 12 O

Two novel quaternary oxyarsenides, Eu Zn As O and Eu Zn As O, were synthesized through metal flux reactions, and their crystal structures were established by single-crystal X-ray diffraction methods. Eu Zn As O crystallizes in the orthorhombic space group , featuring polyanionic ribbons composed of corner-shared triangular [ZnAs ] units, running along the [100] direction. The structure of Eu Zn As O crystallizes in the monoclinic space group 2/ and its anionic substructure can be described as an infinite "ribbonlike" chain comprised of [ZnAs ] trigonal-planar units, although the structural complexity here is greater and also amplified by disorder on multiple crystallographic positions. In both structures, the O anion occupies an octahedral void with six neighboring Eu 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 Eu Zn As O reveal relatively high resistivity ( = 8 Ω·cm) and Seebeck coefficient values ( = 220 μV K ), along with a low concentration and mobility of holes as the dominant charge-carriers ( = 8.0 × 10 cm , = 6.4 cm /V s). Magnetic studies indicate the presence of divalent Eu species in Eu Zn As O and complex magnetic ordering, with two transitions observed at = 21.6 K and = 9 K.