Space-charge mechanism of aging in ferroelectrics: an exactly solvable two-dimensional model

TL;DR

This paper presents an exactly solvable two-dimensional model explaining aging in ferroelectrics through point defect migration driven by local depolarization fields, providing insights into internal bias fields and defect dynamics.

Contribution

It introduces a coupled drift-diffusion model for defect transport and electrostatic relaxation, offering analytical solutions and explaining experimental aging phenomena in ferroelectrics.

Findings

Internal bias field of about 1 kV/mm levels off at low dopant concentrations.

Derived explicit formula for internal bias field showing dependence on time, temperature, and concentration.

Model results align with experimental observations and compare to defect dipole reordering mechanisms.

Abstract

A mechanism of point defect migration triggered by local depolarization fields is shown to explain some still inexplicable features of aging in acceptor doped ferroelectrics. A drift-diffusion model of the coupled charged defect transport and electrostatic field relaxation within a two-dimensional domain configuration is treated numerically and analytically. Numerical results are given for the emerging internal bias field of about 1 kV/mm which levels off at dopant concentrations well below 1 mol%; the fact, long ago known experimentally but still not explained. For higher defect concentrations a closed solution of the model equations in the drift approximation as well as an explicit formula for the internal bias field is derived revealing the plausible time, temperature and concentration dependencies of aging. The results are compared to those due to the mechanism of orientational reordering of defect dipoles.