Pressure-driven chemical lock-in structure and optical properties in Sillen compounds PbBiO2X (X = Cl, Br, and I)

Abstract

Sillen compounds with the general formula of PbBiO₂X (X = Cl, Br, I) are frequently studied as photocatalysts, and have attracted widespread attention due to their degradation of organic contaminants and water oxidation under visible light irradiation. Among many photoelectric materials, the band gap has been reduced approaching to the optimum value by pressure (1.34 eV for photovoltaic materials according to the Shockley–Queisser limit), which is favorable to their photo-responsive applications. However, such enhanced properties are usually restored after the pressure is released. Here, by combining the pressure and chemical engineering tools, we discovered that the optimized structure and optical band gap of PbBiO₂Br could be locked after compression–decompression treatment cycling by selecting appropriate elemental species. The pressure-induced strain retention in PbBiO₂Br could be the cause of the structural and optical irreversible behavior. Moreover, the compression behavior and optical band gap under high pressure in the PbBiO₂X system were studied systematically by in situ high pressure synchrotron X-ray diffraction, UV-vis absorption spectroscopy and resistivity experiments. Along with the enhanced photocurrent under compression, the PbBiO₂X compounds under external pressure exhibited great potential for photocatalytic applications under solar light irradiation. In a suitable element category, the pressure-driven structural lock-in preserves its optical performance, opening up a new window for manipulating and filtrating better multifunctional materials.