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

Ba 2 In 5 P 5 and Ba 2 In 5 As 5 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) Å, b = 4.1599(1) Å, c = 17.4895(2) Å, R 1 = 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; Ba 2+ 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 (ρ RT for Ba 2 In 5 P 5 = 1.0 × 10 −3 Ω cm, and ρ RT Ba 2 In 5 As 5 = 6.1 × 10 −3 Ω cm). NMR studies of the 115 In Knight shifts and the Korringa relationship observed for the temperature dependence of the 31 P resonance of Ba 2 In 5 P 5 characterize these compounds as semiconductors doped into the metallic regime. The flux growth method is the likely source of doping.