First-principles study of barium titanate under hydrostatic pressure

The behavior of the ferroelectric instability of cubic barium titanate under increasing hydrostatic pressure is investigated from first principles. Beyond a rapid suppression and then reappearance of this instability at about 140 GPa, we highlight a sudden change in the dynamical behavior of BaTiO3 at a pressure of approximate to 20 GPa. We show that the ferroelectric instability at high pressure has a totally different character than at atmospheric pressure. From the analysis of the interatomic force constants, we demonstrate that the destabilizing role of the short-range forces at high pressure must be related to the change of the soft mode eigenvector rather than to an original electronic effect.