Synchrotron x-ray Studies of Superlattice Ordering in Pb(Mg1/3Nb2/3)O3 Single Crystals Doped with PbTiO3

TL;DR

This study uses synchrotron x-ray scattering to analyze superlattice ordering in Pb(Mg1/3Nb2/3)O3 single crystals doped with PbTiO3, revealing temperature-dependent nanoregions and their relation to relaxor ferroelectric behavior.

Contribution

It provides detailed insights into the temperature dependence of superlattice reflections and nanoregion formation in PMN-PT crystals, linking these to dielectric properties.

Findings

Alpha spots indicate correlated anti-parallel atomic displacements.

Displacements increase below the freezing temperature T_f.

T_f correlates with dielectric maximum T_m.

Abstract

The temperature dependence of the superlattice reflections: a) F spots and b) alpha spots in a lead magnesium niobate (PMN) single crystals containing 0% and 6% of PbTiO3 (PT) has been studied using synchrotron x-ray scattering techniques. (No superlattice reflections were found in PMN doped with 32% PT). Analysis of the temperature dependence of the alpha spots suggests the existence of the correlated anti-parallel atomic displacements that form nanoregions different from the chemical nanodomains. While the correlation length is temperature independent, the magnitude of these displacements increases on cooling below the freezing temperature Tf. Intensities of the alpha spots above this temperature become indistinguishable from the background. Our results show that value of Tf for each composition is very close to the one obtained from a Vogel-Fulcher fit to the frequency dependence of the dielectric constant maximum Tm. The relation of these correlated anti-ferrodistortive fluctuations to polar ferroelectric nanodomains and relaxor behavior needs further study.