Local Structure and Macroscopic Properties in PMN-PT and PZN-PT solid solutions

TL;DR

This study uses density functional theory to analyze local structures in PMN-PT and PZN-PT solid solutions, revealing how cation displacements influence phase transitions and dielectric properties.

Contribution

It provides a detailed explanation of cation displacement mechanisms and their impact on phase behavior in PMN-PT and PZN-PT systems, highlighting the role of Zn off-centering.

Findings

Zn ions off-center in PZN-PT, enabling larger Pb and Nb/Ti displacements

A quadratic relationship between cation displacements and dielectric temperature maximum

Off-centering behavior correlates with phase transitions in PZN-PT

Abstract

We have examined the local structure of PMN-PT and PZN-PT solid solutions using density functional theory. We find that the directions and magnitudes of cation displacement can be explained by an interplay of cation-oxygen bonding, electrostatic dipole-dipole interactions and short-range direct and through oxygen Pb-B-cation repulsive interactions. We find that the Zn ions off-center in the PZN-PT system, which also enables larger Pb and Nb/Ti displacements. The off-centering behavior of Zn lessens Pb-B-cation repulsion, leading to a relaxor to ferroelectric and a rhombohedral to tetragonal phase transition at low PbTiO$_3$ content in the PZN-PT system. We also show that a simple quadratic relationship exists between Pb and B-cation displacements and the temperature maximum of dielectric constant, thus linking the enhanced displacements in PZN-PT systems with the higher transition temperatures.