Flux Growth and Electronic Properties of Ba2In5Pn5 (Pn = P, As): Zintl Phases Exhibiting Metallic Behavior

Ba2In5P5 and Ba2In5As5 were grown from the reaction of barium and the pnictogen elements in indium flux. These Zintl phases feature a new structure type in orthorhombic space group Pnma (for the phosphorus analogue, a = 17.2572(2) A, b = 4.1599(1) A, c = 17.4895(2) A, R1 = 0.0376). The layered structure features anionic slabs of interconnected main group atoms, with hexagonal channels defined by In−In bonds and capped on the outer edges by the pnictides; Ba2+ cations reside in between these layers. Despite the apparently charge-balanced nature of the structure and the band gaps indicated in density of states calculations, the rising resistivities with increasing temperature indicate these materials behave as metals (ρRT for Ba2In5P5 = 1.0 × 10−3 Ω cm, and ρRT Ba2In5As5 = 6.1 × 10−3 Ω cm). NMR studies of the 115In Knight shifts and the Korringa relationship observed for the temperature dependence of the 31P resonance of Ba2In5P5 characterize these compounds as semiconductors doped into the metallic regime....