New layered quaternary Zintl pnictide oxides Ba2Zn2Pn2O (Pn = Sb, Bi): Discovery, crystal structures, band engineering, and transport properties

Three new heteroanionic oxypnictides, Ba₂Zn₂Sb₂O, Ba₂Zn₂Bi₂O, and the solid solution Ba₂Zn₂Sb_2−xBi_xO (x ≈ 1.1–1.6), have been synthesized and structurally characterized. They are isostructural with their Mn-bearing analog, adopting the Ba₂Mn₂Sb₂O-type structure (space group P6₃/mmc, No. 194), and feature a double-layered 2D $\begin{array}{c}2\\ \infty \end{array}$ [Zn₂Pn₂O]^2- substructure (Pn = Sb, Bi, Sb/Bi) composed of corner-sharing, distorted tetrahedral ZnPn₃O units. Electronic structure calculations reveal a systematic progression from semiconducting Ba₂Zn₂Sb₂O to metallic Ba₂Zn₂Bi₂O as Bi content increases. These trends are corroborated by transport property measurements, with Ba₂Zn₂Sb_0.9(1)Bi_1.1O exhibiting relatively low electrical resistivity, high Hall mobilities of ∼160 cm²/V·s, and large Seebeck coefficients from 69 to 132 μV K⁻¹ over the 300–600 K temperature range. Comparison with structurally related Zintl pnictides, such as SrIn₂As₂ and PrZn₃As₃ phases, situates Ba₂Zn₂Pn₂O (Pn = Sb, Bi) within a broader family of heteroanionic oxypnictide Zintl compounds, highlighting their structural flexibility and amenability to band engineering. Electronic structure and bonding considerations point to tunable semiconducting behavior and underscore the relevance of these materials for thermoelectric and topological applications.