Anti-ferrodistortive Nanodomains in PMN Relaxor

TL;DR

This study reveals anti-ferrodistortive nanodomains in PMN relaxors through x-ray scattering, showing their independence from other nanoregions and their role in relaxor behavior near 220 K.

Contribution

First identification of anti-ferrodistortive nanoregions in PMN, distinguishing them from chemical and ferroelectric nanodomains, and linking them to relaxor phase transitions.

Findings

Anti-ferrodistortive nanoregions exist in PMN.

AFR are distinct from chemical nanodomains and PNR.

AFR correlate with the relaxor phase transition at ~220 K.

Abstract

Temperature dependent studies of the 1/2(hk0) superlattice reflections \alpha spots by synchrotron x-ray scattering measurements were performed in (PMN) and (PMN-xPT) with Ti doping x<0.32 single crystals. Separation of the \alpha spots from the underlying diffuse scattering background allowed studying them as separate entities for the first time. Structure factor calculations have shown that alpha spots constitute the presence of a new kind of anti-ferrodistortive nanoregions (AFR) in the form of fluctuations produced by anti-parallel short-range correlated <110> Pb^2+ displacements. AFR appear to be different and unrelated to the chemical nanodomains (CND) and ferroelectric polar nanoregions (PNR). Simultaneous presence of AFR and PNR can explain relaxor behavior as a result of competition between randomly occurring ferroelectric and anti-ferroelectric fluctuations. Temperature dependence of the \alpha spots in PMN showed a direct correlation with the freezing phase transition near Tf~220 K.