Impedance spectroscopy of ferroelectrics: The domain wall pinning element

TL;DR

This paper develops an equivalent-circuit model to analyze how domain wall motion affects the impedance of ferroelectric materials, revealing different dynamic regimes and coupling effects through experimental impedance spectroscopy and Rayleigh analysis.

Contribution

It introduces a novel equivalent-circuit element based on interface pinning theory to interpret impedance spectra related to domain wall dynamics in ferroelectrics.

Findings

Identified frequency- and amplitude-dependent domain wall regimes.

Quantified coupling between dielectric nonlinearity and dispersion.

Constructed a schematic diagram of domain-wall-motion regimes.

Abstract

We introduce an equivalent-circuit element based on the theory of interface pinning in random systems, to analyze the contribution of domain wall motion below the coercive field to the impedance of a ferroelectric, as a function of amplitude $E_0$ and frequency $f$ of an applied ac electric field. We investigate capacitor stacks, containing ferroelectric 0.5(Ba$_{0.7}$Ca$_{0.3}$)TiO$_{3}$--0.5Ba(Zr$_{0.2}$Ti$_{0.8}$)O$_{3}$ (BCZT) thin films, epitaxially grown by pulsed laser deposition on Nb-doped SrTiO$_3$ single crystal substrates and covered with Au electrodes. Impedance spectra from $f=10$\,Hz to 1\,MHz were collected at different $E_0$. Deconvolution of the spectra is achieved by fitting the measured impedance with an equivalent-circuit model of the capacitor stacks, and we extract the domain-wall-motion induced amplitude- and frequency-dependent dielectric response of the BCZT films from the obtained fit parameters. From an extended Rayleigh analysis, we quantify the coupling strength between dielectric nonlinearity and dielectric dispersion in the BCZT films and identify different domain-wall-motion regimes. Finally, we construct a schematic diagram of the different domain-wall-motion regimes and discuss the corresponding domain-wall dynamics.