Dielectric Response in Ferroelectrics Near Polarization Switching: Analytical Calculations, First-Principles Modeling, and Experimental Verification

Abstract

Ferroelectrics (FEs) are increasingly used in nonvolatile memory applications. However, the impact of the electric dipole switching on its material parameters, in particular on the dielectric response, is not fully understood. In this work, an analytical model, linking the dielectric response to the potential energy curve, is first used to qualitatively illustrate the nonconstant evolution of the dielectric response with applied electric field. Increasing precision, we then show from first-principles density functional theory simulations that defect-free FE materials undergo changes in potential energy near the FE switching that lead to vibrational modes softening, which impacts the dielectric response. In particular, we observe that the dielectric response <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon $ </tex-math></inline-formula> of an FE material with antialigned polarization increases as the applied electric field increases toward the coercive field. We incorporate this new insight in the time-dependent NLS-based predictions and demonstrate that this evolution of the dielectric response right before polarization reversal is required for a proper match between experiment and prediction of the capacitance–voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CV</i> ) characteristics of the metal–ferroelectric–metal (MFM) capacitor.