Physical phenomena in lead magnoniobate-ferroelectric material with a smearing phase transformation

The review of results of investigations of electrooptical, elastic optical and a number of other effects in the range of diffuse phase transition (DPT) in lead magn.esium niobate, is given. It in shown that changes in the state of polar regions and damains affect many physical phenome-- na in the range of DPT and cause the unusual behaviour of non-linear properties, while composition fluctuations bring about the appearance of large-scale inhomogeneities as compared with correlation radius. When explaining the peculiarities of the appoaring system it in recommended to consider the effect of boundaries of small regions of coexisting phases