Migration of Charged Defects in Local Depolarization Fields as a Mechanism of Aging in Ferroelectrics

Abstract

Quasistatic dielectric relaxation due to migration of charged point defects is considered as a mechanism of aging in ferroelectrics. A two-dimensional model is developed which includes the coupled potential problem and the field-driven diffusion problem. Numerical study reveals formation of space charge zones near the grain boundaries with the only characteristic time of several days being the Maxwell relaxation time defined by the charge carrier density and mobility. The clamping pressure due to charge segregation is about few MPa which corresponds to observed coercive stresses in perovskite ferroelectrics and is significantly stronger than in the mechanisms involving orientational reordering of defect dipoles.