Understanding physical chemistry of BaSr_1-TiO₃ using ReaxFF molecular dynamics simulations

Barium strontium titanate BaSr_1-TiO₃ (BSTO) has been widely used in nano devices due to its unique ferroelectric properties and can be epitaxially grown on a SrTiO₃ (STO) support, with a reduced lattice and thermal mismatch. In this work, we developed a ReaxFF reactive force field verified against quantum mechanical data to investigate the temperature and composition dependency of BSTO in non-ferroelectric/ferroelectric phases. This potential was also explicitly designed to capture the surface energetics of STO with SrO and TiO₂ terminations. Our molecular dynamics simulations indicate that when the percentage of Sr increases, the phase transition temperature and the polarizations of the BaSr_1-TiO₃ system decrease monotonically. In addition, as the oxygen vacancy concentration enhances, the initial polarization and the phase transition temperature of the system drop significantly. Furthermore, our simulation results show that charge screening induced by adsorption of water molecules on TiO₂ terminated surfaces leads to an increased initial polarization.