Domain structure in the monoclinic Pm phase of Pb(Mg1/3Nb2/3)O3 - PbTiO3 single crystals

TL;DR

This study investigates the domain structure of Pb(Mg1/3Nb2/3)O3 - PbTiO3 single crystals near the morphotropic phase boundary, revealing a monoclinic Pm phase with specific domain arrangements and wall types, confirmed by microscopy and diffraction.

Contribution

It provides the first detailed analysis of domain structures in the monoclinic Pm phase of these crystals near the MPB, linking theoretical predictions with experimental observations.

Findings

Monophase state with monoclinic Pm structure confirmed.

Presence of 180° domain walls in unpoled crystals.

Distinct domain wall orientations in poled crystals.

Abstract

The domain structure of (1-x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 single crystals with composition x ~ 0.33 in the range of the morphotropic phase boundary (MPB) was studied. Based on the analysis of spontaneous strain compatibility and charge of domain walls, we have established the permissible domain arrangements for the ferroelectric phases of different symmetry, which are expected to occur in the range of the MPB. Examination of (001)-oriented unpoled and electrically poled (along the [001] direction) crystal plates in polarizing microscope reveals a monophase state with the domain structure compatible with the structure theoretically predicted for the Mc monoclinic phase (space group Pm), which was recently discovered in the compositions close to the MPB by x-ray and neutron diffraction studies. In the unpoled crystal the 180 deg. walls between the domains whose spontaneous polarization vectors are parallel to the plane of the crystal plate (i.e. a-domains) are observed. The domain structure of the poled crystal is predominantly composed of crystallographically prominent Wf walls parallel to (001) (i.e. the plane of the crystal plate) and inclined S walls parallel to [110] or [1-10] direction. In poled and unpoled samples the optical rotatory polarization effect is found, which is related to the inhomogeneity of the sample resulting from the mixture of domains.