Rayleigh analysis and dielectric dispersion in polycrystalline 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 ferroelectric thin films by domain-wall pinning element modeling

We use impedance spectroscopy to investigate the dielectric response in polycrystalline, lead-free 0.5(Ba-0.Ca-7(0.3))TiO3-0.5Ba(Zr0.2Ti0.8)O-3 (BCZT) ferroelectric thin films as a function of amplitude E-0 and frequency f of an applied ac electric field. Impedance spectra from f = 10 Hz to 1 MHz were collected at different E-0 on polycrystalline BCZT capacitor stacks, grown by pulsed laser deposition on platinized Si substrates and covered with Au electrodes. Deconvolution of the spectra is achieved by fitting the measured impedance to the impedance of an equivalent-circuit model of the capacitor stacks, including a recently proposed domain-wall pinning element ZDW. From an extended data analysis, we quantify the coupling strength between dielectric nonlinearity and frequency dispersion in the BCZT thin films, and we obtain a schematic diagram of the different domain-wall-motion regimes. Our results indicate that the presence of grain boundaries in BCZT reduces the coupling strength and suppresses the motion of internal domain-wall segments and also the irreversible center-of-mass motion of the domain walls.