History-dependent and frequency-dependent dielectric nonlinearities induced by polar nanoregions in a thin film of 0.5 ( Ba 0.7 Ca 0.3 TiO 3 ) -- 0.5 ( BaZr 0.2 Ti 0.8 O 3 )

TL;DR

This study investigates dielectric nonlinearities in a specific thin film, revealing how polar nanoregions influence hysteresis behavior and how their configurations can be altered by cycling and measurement conditions.

Contribution

It demonstrates the frequency-dependent and history-dependent dielectric nonlinearities caused by polar nanoregions in the thin film, using impedance spectroscopy and harmonic analysis.

Findings

Pinched hysteresis loops are stronger at low frequencies.

Polar nanoregions' responses change with cycling, affecting hysteresis shape.

FORC analysis reveals shifts from pinched to soft ferroelectric states.

Abstract

In this article, dielectric nonlinearities in 0.5(Ba0.7 Ca0.3 TiO3 ) -- 0.5(BaZr 0.2 Ti0.8 O3 ) thin film are studied using impedance spectroscopy and harmonic measurements, as a function of the AC measuring field, at different frequencies and upon cycling. The measurements reveal that the pinching of the hysteresis loop, characterized by a phase angle of the third harmonic close to --270 deg, is stronger for low frequencies. This confirms that the pinching is induced by the presence of polar nanoregions (PNRs), whose responses are also strongly dependent on frequency. When repeating the measurement, the PNR contribution changes since the phase angle of the third-harmonic response evolves from pinched to conventional relaxor. This shows that strong changes in the PNR configuration can be induced, even for low AC fields. First-order reversal curves (FORCs) confirm the presence of a pinched hysteresis loop. When repeating the FORC measurement a second time, the distribution drastically changes and corresponds to a soft ferroelectric. The asymmetry of the Preisach plane measured using FORCs is confirmed by a proposed measurement strategy: unipolar impedance measurements.