Optical study of the spontaneous ferroelectric phase transition in lead scandoniobate single crystals

A study is reported of the optical transmission and small-angle light scattering (SAS) in ordered and disordered stoichiometric single crystals of lead scandoniobate (PSN) with a zero and a dc electric field applied. It is shown that the spontaneous phase transition occurring in both crystals is accompanied by a sharp peak in SAS intensity, which implies the percolation nature of this transition. A field-temperature phase diagram has been constructed for the PSN single crystals studied in the work.