Negative Slope Polarization in Ferroelectric Hysteresis Loop Engineered by Defect Dipoles

Abstract

The power dissipation in conventional nanoelectronic devices is facing a fundamental barrier of Boltzmann Tyranny. The negative capacitance in ferroelectric materials provides possible solution to overcome this impending problem, and thus the corresponding research has received a great deal of attention. Here we report a novel method to design negative capacitance in ferroelectrics by defect-dipole engineering based on the results from both simulation and experiments. By the molecular dynamics simulations of a first principles-based effective Hamiltonian, the abnormal polarization with negative slope is 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, which can be used to achieve negative capacitance. This negative slope polarization is attributed to the fact that the polarization overshoots, oscillates and finally gradually switches to the direction of defect dipoles during the polarization switching at the coercive field due to the restoring force of the defect dipoles. The P-E loop exhibits the abnormal polarization only at a certain range of defect level, while 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 when the electric field is applied perpendicular to the poling direction, which are in good agreement with the simulation results.

Keywords: ferroelectrics, negative capacitance, molecular dynamics simulation, defect-dipole engineering