Negative slope polarization in ferroelectric hysteresis loop engineered by defect dipoles

The power dissipation in conventional microelectronic devices is facing a fundamental barrier of Boltzmann Tyranny. The negative capacitance (NC) effect in ferroelectric materials provides possible solution to overcome this impending problem and gets a lot of attention. Here we report a novel method to design negative capacitance in ferroelectrics by the introduction of defect-dipole engineering. In the molecular dynamics simulations of a first principles-based effective Hamiltonian, an abnormal polarization with negative slope and corresponding differential capacitance are observed in the polarization-electric field (P-E) hysteresis loops when the applied electric field is perpendicular to the direction of the defect dipoles in acceptor-doped BaTiO3 single crystals. This phenomenon is attributed to the fact that the polarization overshoots, oscillates and finally gradually switches to the direction of defect dipoles by their restoring forces during the polarization switching near the coercive field. The P-E loop exhibits abnormal NC response only at a certain range of defect levels, and there are double loops at high level and typical square-shaped loops at low level. Moreover, in the experiments of poled 1 mol.% Mn-doped BaTiO3 ceramics, the abnormal negative slope polarization in P-E loops is confirmed, which are in good agreement with the simulation results. [Display omitted]