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

Two novel quaternary oxyarsenides, EuZnAsO and EuZnAsO, were synthesized through metal flux reactions, and their crystal structures were established by single-crystal X-ray diffraction methods. EuZnAsO crystallizes in the orthorhombic space group , featuring polyanionic ribbons composed of corner-shared triangular [ZnAs] units, running along the [100] direction. The structure of EuZnAsO 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 EuZnAsO 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 EuZnAsO and complex magnetic ordering, with two transitions observed at = 21.6 K and = 9 K.