Optically Isotropic and Monoclinic Ferroelectric Phases in PZT Single Crystals near Morphotropic Phase Boundary

TL;DR

This study reveals scale-dependent symmetry changes in PZT single crystals near the morphotropic phase boundary, showing optical isotropy at small scales and monoclinic phases at larger scales, linked to domain size variations.

Contribution

It uncovers the existence of optically isotropic and monoclinic ferroelectric phases in PZT crystals, highlighting the role of domain size in symmetry properties.

Findings

Sub-micrometer tetragonal domains exhibit optical cubic symmetry.

Larger domains transform into monoclinic Cm phase upon cooling.

Optical isotropy is due to small domain size, not overall crystal symmetry.

Abstract

We report the finding of unusual scale-dependent symmetry below the ferroelectric Curie temperature in the perovskite Pb(Zr1-xTix)O3 single crystals of morphotropic phase boundary compositions. The crystals of tetragonal symmetry (from x-ray diffraction experiments) on sub-micrometer scale exhibit a macroscopic (optically determined) cubic symmetry. This peculiar optical isotropy is explained by the anomalously small size of tetragonal ferroelectric domains. Upon further cooling the crystals transform to the phase consisting of micrometer-sized domains of monoclinic Cm symmetry.