Thermoelectric Properties of As-Based Zintl Compounds Ba_1–xK_xZn₂As₂

As-based Zintl compounds Ba_1–xK_xZn₂As₂ were prepared by solid-state reaction followed by hot pressing. Ba_1–xK_xZn₂As₂ (x ≤ 0.02) crystallizes in the α-BaCu₂S₂-type structure (space group Pnma) upon cooling from 900 °C, whereas it crystallizes in the ThCr₂Si₂-type structure (space group I4/mmm) for x ≥ 0.04. The lattice thermal conductivities are almost equivalent for both crystal structures with relatively low values of 0.8–1.1 W/mK at 773 K. The values are comparable to those of Sb-based Zintl compounds, though Ba_1–xK_xZn₂As₂ consists of As atoms, which are lighter than Sb atoms. The electrical resistivity and Seebeck coefficient decreases with increasing x, indicating successful hole doping by K substitution. The dimensionless figure-of-merit ZT is 0.67 at 900 K for x = 0.02, opening a new class of thermoelectric materials with the As-based 122 Zintl compounds.