Synthesis, Crystal Structure, and Photoelectric Properties of a New Layered Bismuth Oxysulfide

[Bi2O2]-containing tetragonal compounds have received enormous attention due to unique functions including ferroelectricity, photocatalysis, and superconductivity. Here, a new layered compound Bi9O7.5S6 was synthesized via a facile hydrothermal route. The compound, belonging to a new structure type crystallizes in a rhombohedral system with space group R3̅m (a = 4.0685(1) Å, c = 31.029(5) Å, V = 444.8(1) Å(3), Z = 1). The overall crystal structure consists of alternatively packed unique [Bi2O2] and [BiS2] layers along [001] which are combined with each other by van der Waals interaction. The phase purity of the product is confirmed by powder X-ray diffraction. XPS analyses indicate +3 for Bi and -2 for S atoms. The temperature dependence of resistivity ρ(T) indicates that the semiconducting sample follows the mechanisms of variable range hopping (VRH) and adiabatic small polaron hopping (SPH). The direct-transition band gap, Eg = 1.27 eV derived from optical absorption spectrum, falls in the optimal region of solar absorber materials. Accordingly, the photoelectric measurement demonstrates the potential for applications for photovoltaic devices.