Density functional theory study of hypothetical PbTiO3 -based oxysulfides

Using density functional theory (DFT) within the local density approximation (LDA), we calculate the physical and electronic properties of PbTiO3 (PTO) and a series of hypothetical compounds PbTiO3-xSx x=0.2, 0.25, 0.33, 0.5, 1, 2, and 3 arranged in the corner-sharing cubic perovskite structure. We determine that replacing the apical oxygen atom in the PTO tetragonal unit cell with a sulfur atom reduces the x=0 LDA calculated band gap of 1.47 eV to 0.43-0.67 eV for x=0.2-1 and increases the polarization. PBE0 and GW methods predict that the compositions x=0.2-2 will have band gaps in the visible range. For all values of x < 2, the oxysulfide perovskite retains the tetragonal phase of PbTiO3, and the a lattice parameter remains within 2.5% of the oxide. Thermodynamic analysis indicates that chemical routes using high-temperature gas, such as H2S and CS2, can be used to substitute O for S in PTO for the compositions x=0.2-0.5.