Dielectric aging and its temperature dependence in ferroelectric ceramics

Abstract

In acceptor doped perovskite type ceramics the decrease of the complex dielectric constant and the build-up of electric and elastic internal bias fields are caused by the slow orientation of dipolar defects. Isothermal aging measurements have confirmed the strong correlation between the alignment of the defect dipoles and the dielectric aging as quantitatively described by a clamping model. In this paper simultaneous measurements of both properties, dielectric constant and electric internal bias field in a wide temperature range are discussed and explained. The measurements were carried out on Fe doped lead zirconate titanate (PZT) ceramics at different frozen in aging states. At low temperatures the defects are immobile, nevertheless the internal bias and the dielectric constant depend strongly on temperature. The dielectric constant in this temperature range is governed by thermally activated relaxations of the domain walls. At higher temperatures the degree of orientation of the defects is time and temperature dependent. Therefore both, the internal bias field and the dielectric constant are time and temperature dependent too. In the low temperature region in which the domain walls become more mobile by thermal activation and simultaneously are clamped by the defects the measurements give clear indications of some selective interaction of these two effects.