K2Ge3As3: Fiberlike Crystals of a Narrow-Band-Gap Zintl Phase with a One-Dimensional Substructure ∞1{(Ge3As3)2–}

The novel ternary phase K2Ge3As3 was prepared by fusion of the elements. It crystallizes in very thin, deeply black fibers exhibiting metallic luster. The appearance is in accordance with its crystal structure that comprises an unprecedented one-dimensional anionic substructure, ∞1{(Ge3As3)2–}, and it reflects its optical absorption properties. Both an experimental UV–visible spectrum and density-functional theory (DFT)-based band structure calculations hint toward a narrow-band-gap semiconductor. The band gap obtained from DFT using the SCAN functional is approximately 1.4 eV, in excellent agreement with the experimental data. We present the synthesis, structure, electronic properties, and bonding character of this new Zintl phase. Impedance spectroscopy reveals similar electronic and ionic conductivity of the phase.