Local structure and macroscopic properties in PbMg1/3Nb2/3O3-PbTiO3 and PbZn1/3Nb2/3O3-PbTiO3 solid solutions -: art. no. 220101

We have examined the local structure of PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) and PbZn1/3Nb2/3O3-PbTiO3 (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 move 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 relaxor-to-ferroelectric and rhombohedral-to-tetragonal phase transitions 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 the dielectric constant, thus linking the enhanced displacements in PZN-PT systems with the higher transition temperatures.