Quaternary Zintl Phases Ba₂InSnP₃ and Ba₂InSnAs₃ with Complex Structures and n-Type Semiconducting Behavior

Presented are the crystal structures and the transport properties of the novel quaternary pnictides with the general formula Ba 3 InSnPn 3 (Pn = P, As). Large single crystals of the phosphide, arsenide, and the P/As solid solution can be readily synthesized by using reactions with molten Sn as a choice of a reactive metal flux. The title compounds crystallize in a monoclinic crystal system with a new structure type. The structure features a 3D polyanionic sublattice of corner- and edge-sharing [M 4 Pn 10 ] units made of double-corner-sharing ethane-like [M 2 Pn 6 ] fragments (M = In/Sn). Comprehensive crystallographic studies, including single-crystal neutron diffraction, confirm the random distribution of In and Sn atoms; i.e., there is no long-range ordering. The equiatomic statistical distribution of In and Sn allows for the simultaneous existence of In–In, Sn–Sn, as well as In–Sn bonds, yielding closed-shell electronic configuration in atypical In 2+ and Sn 3+ states. Partitioning of the valence electrons as (Ba 2+ ) 3 (In 2+ )(Sn 3+ )(Pn 3– ) 3 shows charge-balanced compositions; i.e., the compounds are Zintl phases. The expected valence-precise behavior is corroborated by both electronic structure calculations and electrical resistivity measurements, which show intrinsic narrow band gap semiconductors. Thermal and electrical transport measurements for single-crystalline Ba 3 InSnAs 3 indicate an n-type charge transport mechanism with a relatively low charge-carrier concentration and mobility of electrons as the dominant charge carriers ( n 300K ≈ 1 × 10 17 cm –3, μ 300K ≈ 4 cm 2 /V s).