A tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: the structure of PbZr(0.52)Ti(0.48)O3

TL;DR

This study investigates the detailed crystal structures of tetragonal and monoclinic phases in PbZr(0.52)Ti(0.48)O3 near the morphotropic phase boundary, revealing local displacements and phase relationships crucial for understanding ferroelectric behavior.

Contribution

It provides a detailed Rietveld analysis of the tetragonal and monoclinic phases in PZT at x=0.48, elucidating the local atomic displacements and phase transition mechanisms.

Findings

Identification of local disordered Pb shifts in tetragonal phase.

Monoclinic phase as a condensation of local displacements.

Bridge between tetragonal and rhombohedral phases in MPB region.

Abstract

The perovskite-like ferroelectric system PbZr(1-x)Ti(x)O3 (PZT) has a nearly vertical morphotropic phase boundary (MPB) around x=0.45-0.50. Recent synchrotron x-ray powder diffraction measurements by Noheda et al. [Appl. Phys. Lett. 74, 2059 (1999)] have revealed a new monoclinic phase between the previously-established tetragonal and rhombohedral regions. In the present work we describe a Rietveld analysis of the detailed structure of the tetragonal and monoclinic PZT phases on a sample with x= 0.48 for which the lattice parameters are respectively: at= 4.044 A, ct= 4.138 A, at 325 K, and am= 5.721 A, bm= 5.708 A, cm= 4.138 A, beta= 90.496 deg., at 20K. In the tetragonal phase the shifts of the atoms along the polar [001] direction are similar to those in PbTiO3 but the refinement indicates that there are, in addition, local disordered shifts of the Pb atoms of ~0.2 A perpendicular to the polar axis.. The monoclinic structure can be viewed as a condensation along one of the <110> directions of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along one of the <100> directions recently reported by Corker et al.[J. Phys. Condens. Matter 10, 6251 (1998)] for rhombohedral PZT. The monoclinic structure therefore provides a microscopic picture of the MPB region in which one of the "locally" monoclinic phases in the "average" rhombohedral or tetragonal structures freezes out, and thus represents a bridge between these two phases.