Crystal Engineering of Bi2WO6 to Polar Aurivillius-Phase Oxyhalides

The Aurivillius phases of complex bismuth oxides have attracted considerable attention because of their lattice polarization (ferroelectricity) and photocatalytic activity. We report a first-principles exploration of Bi2WO6 and the crystal engineering through replacing W6+ by pentavalent (Nb5+ and Ta5+) and tetravalent (Ti4+ and Sn4+) ions, with charge neutrality maintained by the formation of a mixed anion oxyhalide sublattice. We find that Bi2SnO4F2 is thermodynamically unstable, in contrast to Bi2TaO5F, Bi2NbO5F, and Bi2TiO4F2. The electric dipoles introduced by chemical substitutions in the parent compound are found to suppress the spontaneous polarization from 61.55 mu C/cm(2) to below 15.50 mu C/cm(2). Analysis of the trends in electronic structure, surface structure, and ionization potentials is reported. This family of materials can be further extended with control of layer thicknesses and choice of compensating halide species.