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 PbTiO3 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.
@article{arxiv.cond-mat/0410337,
title = {Local Structure and Macroscopic Properties in PMN-PT and PZN-PT solid solutions},
author = {Ilya Grinberg and Andrew M. Rappe},
journal= {arXiv preprint arXiv:cond-mat/0410337},
year = {2009}
}