Structural Electronic and Optical Properties of BiOX1−xYx (X Y = F Cl Br and I) Solid Solutions from DFT Calculations

摘要

Six BiOX1−xYx (X, Y = F, Cl, Br, and I) solid solutions have been systematically investigated by density functional theory calculations. BiOCl1−xBrx, BiOBr1−xIx, and BiOCl1−xIx solid solutions have very small bowing parameters; as such, some of their properties increase almost linearly with increasing x. For BiOF1−xYx solid solutions, the bowing parameters are very large and it is extremely difficult to fit the related calculated data by a single equation. Consequently, BiOX1−xYx (X, Y = Cl, Br, and I) solid solutions are highly miscible, while BiOF1−xYx (Y = Cl, Br, and I) solid solutions are partially miscible. In other words, BiOF1−xYx solid solutions have miscibility gaps or high miscibility temperature, resulting in phase separation and F/Y inhomogeneity. Comparison and analysis of the calculated results and the related physical–chemical properties with different halogen compositions indicates that the parameters of BiOX_1−xY_x solid solutions are determined by the differences of the physical–chemical properties of the two halogen compositions. In this way, the large deviation of some BiOX_1−xY_x solid solutions from Vegard’s law observed in experiments can be explained. Moreover, the composition ratio of BiOX_1−xY_x solid solutions can be measured or monitored using optical measurements.