Single‐crystal neutron diffuse scattering and Monte Carlo study of the relaxor ferroelectric PbZn 1/3 Nb 2/3 O 3 (PZN)

Full three‐dimensional diffuse neutron scattering data have been recorded from a single crystal of Pb(Zn 1/3 Nb 2/3 )O 3 (PZN) at 300 K using the time‐of‐flight Laue technique on the SXD single‐crystal instrument at ISIS. The data show a series of diffuse rods of scattering oriented parallel to each of the six 〈1 1 0〉 crystal directions. Monte Carlo simulation has been used to demonstrate that the diffuse rods are caused by planar nanodomains oriented normal to the 〈1 1 0〉 directions. Within these domains, there are correlated displacements of the atoms away from their average site positions. In order to explain the systematic absence of some rods of scattering in the ( h   k  1) data but the presence of all rods in the ( h   k  0) data, it is necessary that the displacement of an O atom is of opposite sign to that of its neighbouring Pb atoms. This is explained in terms of a model based on the fact that Pb 2+ possesses a lone pair of electrons, giving the Pb ion directionality.