Phase transition and polar cluster behavior above Curie temperature in ferroelectric BaTi$_{0.8}$Zr$_{0.2}$O$_3$

TL;DR

This study investigates the phase transition and polar nanostructure behavior in BaTi$_{0.8}$Zr$_{0.2}$O$_3$ above its Curie temperature, revealing local structures and remnant polarization linked to polar nanoclusters.

Contribution

It provides new insights into the existence of polar nanostructures and remnant polarization above Tc in ferroelectric BaTi$_{0.8}$Zr$_{0.2}$O$_3$, highlighting their role in dielectric and piezoelectric properties.

Findings

Remnant polarization persists up to ~350 K.

Polar nanostructures reorient above Tc.

Elastic response and piezoelectricity observed above Tc.

Abstract

We study the phase transition behavior of the ferroelectric BaTi$_{0.8}$Zr$_{0.2}$O$_3$ in the paraelectric region. The temperature dependencies of thermal, polar, elastic and dielectric properties indicate the presence of local structures above the paraelectric-ferroelectric transition temperature Tc = 292 K. The non-zero remnant polarization is measured up to a characteristic temperature T* ~350 K, which coincides with the temperature where the dielectric constant deviates from Curie-Weiss law. Resonant Piezoelectric Spectroscopy shows that DC field-cooling above Tc using fields smaller than the coercive field leads to an elastic response and remnant piezoelectricity below T*, which likely corresponds to the coherence temperature associated with polar nanostructures in ferroelectrics. The observed remnant effect is attributed to the reorientation of polar nanostructures above Tc.