Chemical Ordering, Local Structure and Diffuse Scattering from Lead Scandium Niobate

The ferroelectric perovskite PbSc_1/2Nb_1/2O₃ (PSN) can have varying degrees of chemical ordering between scandium and niobium; typical growth methods achieve long-range alternation between the two atom species and a more purely ferroelectric state, but fast quenching from high temperature can freeze the two into a short-range ordered state with enhanced dielectric properties and a more relaxational ferroelectric character. This provides an opportunity to examine the influence of chemical short-range order on other types of structural short-range order, which are in turn responsible for bulk dielectric and ferroelectric properties. Single crystal diffuse x-ray scattering measurements were taken of both long-range and short-range chemical ordered samples of PSN as a function of temperature, providing large volumes of reciprocal space in which to track the evolution of key structural features. The contrasting chemical orders are clearly visible in scattering data, but features related to local antiferroelecticity and ferrodistortive regions also change with chemical ordering: additional temperature-dependent superstructure peaks far more prominent in chemically ordered PSN and the “butterfly” scattering associated with ferrodistortive regions more persistent in chemically unordered PSN.