Chemical origin of nanoscale polar domains in PbZn 1/3 Nb 2/3 O 3

Abstract

We describe the development of an atom-based Monte Carlo simulation model which gives rise to a nanoscale polar domain structure as envisaged to occur in Pb (Zn1 3 Nb2 3) O3 (PZN) and similar relaxor ferroelectric materials. Individual domains are essentially thin platelike domains normal to each of the six 110 directions. Calculated diffuse scattering patterns have been obtained from the simulations, and these are in good agreement with observed neutron scattering data. Nanoscale domain formation is driven by the need for the Pb atoms to satisfy their valence requirements; within a planar domain, the Pb atoms are displaced in a concerted fashion away from the center of their 12-fold coordination polyhedra with an in-plane displacement along 110 towards one of the coordinating O atoms. The B -site cations Zn and Nb display a strong tendency to alternate in the 100 directions but complete order is frustrated by the 2:1 stoichiometry. No diffraction evidence has been found that this B -site ordering is directly linked to the nanoscale polar domain ordering. Such a linkage cannot be completely ruled out, but if it does exist, its effect on the diffraction pattern must be quite subtle. The B -site ordering does play an indirect role in establishing the average cell dimension, which in turn dictates the magnitude of the Pb displacements. The effect of applying an external electric field is modeled, and the results are found to be consistent with experiment.