Oxygen vacancies induced ferroelectricity in relaxors with ABO3 structure

TL;DR

This paper explores how oxygen vacancies can induce ferroelectricity in relaxor materials with ABO3 perovskite structures, using phenomenological theory to analyze their influence on polar properties and phase coexistence.

Contribution

It introduces a theoretical framework incorporating oxygen vacancy effects into relaxor ferroelectrics, demonstrating how vacancies can induce ferroelectricity and alter phase behavior.

Findings

Oxygen vacancies can turn negative Curie temperatures positive at sufficient concentrations.

Vacancies influence local polarization and electric fields via flexo-chemical coupling.

Coexistence of ferroelectric and relaxor phases is possible due to vacancy inhomogeneity.

Abstract

The consideration of oxygen vacancies influence on the relaxors with perovskite structure was considered in the framework of Landau-Ginzburg-Devonshire phenomenological theory. The theory applicability for relaxors is based on the existence of some hidden soft phonon polar mode in them, and its frequency could be zero at some negative temperature TC*. Main attention was paid to PZN-PLZT relaxor described by formula 0.3Pb(Zn1/3Nb2/3)O3-0.7(Pb0.96La0.04(ZrxTi1-x)0.99O3) with x = 0.52, where earlier experimental investigation of oxygen vacancies influence on the polar properties was performed and the evidence of oxygen vacancies induced ferroelectricity was obtained. Since the oxygen vacancies are known to be elastic dipoles, they influence upon elastic and electric fields due to Vegard and flexoelectric coupling. We include the vacancies elastic and electrostrictive contribution into free energy functional. The calculations of the vacancies impact on polar properties were performed using their concentration distribution function. It was shown that the negative Curie temperature of a relaxor TC* is renormalized by the elastic dipoles due to the electrostrictive coupling and can become positive at some large enough concentration of the vacancies. We calculated the local polarization and electric field induced by the flexo-chemical coupling in dependence on the concentration of oxygen vacancies. The coexistence of FE phase and relaxor state can take place because of inhomogeneity of vacancies concentration distribution.