Atomistic studies of temporal characteristics of polarization relaxation in ferroelectrics

Abstract

Polarization relaxation fundamentally determines the speed, energy consumption, and functionality of ferroelectric materials and devices, which is considered as the core aspect of ferroelectric-based applications and attracts considerable attention. The relaxation time, describing the temporal characteristics of polarization relaxation, has been reported to vary from subpicoseconds to hundreds of nanoseconds in ferroelectrics, and the microscopic picture is still an open question. In this paper, starting from atomistic models for ferroelectrics, a generalized Langevin equation is proposed to describe the dynamical behaviors of polarization at the mesoscale or macroscale. On one hand, through the artificial construction of adiabatic processes, it is derived that the relaxation time is connected with the lifetimes of the phonon modes involved in a many-body ferroelectric system, bridging the thermodynamics of polarization with the dissipation behavior of the phonon modes at the microscale. On the other hand, the relaxation time is then linked to the kinetic coefficient used in the time-dependent Ginzburg-Landau equation, for the polarization evolution on the meso- or macroscale. Furthermore, based on driven Brownian motion, we propose a theoretical model of the dependence of the polarization switching time with an applied external electric field on a ferroelectric monodomain system. The prediction of the switching time is found to agree well with the dynamical simulation data, which verifies the applicability and reliability of the physical picture of the relaxation time clarified in the current work. Our discussion of the physical picture of the polarization relaxation time provides useful ideas for the development of multiscale modeling method for ferroelectrics.