Synchrotron X-ray scattering study of lead magnoniobate relaxor ferroelectric crystals

Results of a synchrotron radiation scattering study of single crystals of relaxor ferroelectric lead magnoniobate (PMN) are presented. It is demonstrated that the diffuse scattering could be separated into two components-longitudinal Huang scattering related to the deformation of lattice and transverse ferroelectric fluctuations (FF) scattering. It is shown that at large q, where q is the deviation in the scattering vector from the reciprocal lattice point, FF scattering follows a q(-alpha) power law. As the temperature is decreased the power exponent alpha changes from 2.3 to 2.7 through T-g = 230 K where the freezing of FF takes place. Strong asymmetry of the lineshape for the transverse scan in the vicinity of the (230) reciprocal lattice point is observed. This may be explained in terms of the strong linear coupling between the ferroelectric fluctuations and the lattice deformation. In addition two types of diffuse superlattice diffraction peaks, at 1/2(111) and 1/2(110), have been observed for the first time with X-ray diffraction.