Origin of diffuse scattering in relaxor ferroelectrics

High-pressure and variable temperature single-crystal synchrotron x-ray measurements combined with first principles based molecular-dynamics simulations were used to study diffuse scattering in the relaxor ferroelectric system PbSc_1/2Nb_1/2O₃. Constant temperature experiments show a pressure-induced transition to the relaxor phase, in which butterfly- and rod-shaped diffuse scattering occurs around the {h00} and {hh0} Bragg spots. Simulations qualitatively reproduce the observed diffuse scattering features as well as their pressure-temperature behavior and show that they arise from polarization correlations between chemically ordered regions, which in previous simulations were shown to behave as polar nanoregions. Simulations also exhibit radial diffuse scattering [elongated toward and away from Q= (000)] that persists even in the paraelectric phase; consistent with previous neutron experiments on PbMg_1/3Nb_2/3O₃.