Coexistence and competition of local- and long-range polar orders in a ferroelectric relaxor

TL;DR

This study investigates how local polar regions in a relaxor ferroelectric change with temperature and electric field, revealing coexistence and competition between local and long-range polar orders through neutron scattering.

Contribution

It provides new insights into the behavior of polar nanoregions and their response to temperature and electric fields in a relaxor ferroelectric material.

Findings

Diffuse scattering increases with cooling, indicating evolving local polar order.

Electric field alters diffuse scattering shape but does not eliminate it, showing PNR redistribution.

Changes in atomic displacement ratios within PNR are linked to scattering variations.

Abstract

We have performed a series of neutron diffuse scattering measurements on a single crystal of the solid solution Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (PZN) doped with 8% PbTiO$_3$ (PT), a relaxor compound with a Curie temperature T$_C \sim 450$ K, in an effort to study the change in local polar orders from the polar nanoregions (PNR) when the material enters the ferroelectric phase. The diffuse scattering intensity increases monotonically upon cooling in zero field, while the rate of increase varies dramatically around different Bragg peaks. These results can be explained by assuming that corresponding changes occur in the ratio of the optic and acoustic components of the atomic displacements within the PNR. Cooling in the presence of a modest electric field $\vec{E}$ oriented along the [111] direction alters the shape of diffuse scattering in reciprocal space, but does not eliminate the scattering as would be expected in the case of a classic ferroelectric material. This suggests that a field-induced redistribution of the PNR has taken place.