Order and disorder in the relaxor ferroelectric perovskite PbSc1/2Nb1/2O3 (PSN): comparison with simple perovskites BaTiO3 and PbTiO3

We report a structural evolution analysis of the long-range and local order and disorder of lead scandium niobate PbSc1/2Nb1/2O3 (PSN) down to 10 K, using a combination of neutron and x-ray diffraction on powder and single crystals. The structure of PSN is discussed and compared with those of simple perovskite compounds BaTiO3 and PbTiO3. In PSN the existence of a long-range but still disordered ferroelectric phase, different from those of simple perovskites, is evidenced. The disorder of lead and scandium/niobium atoms on short-, medium-and long-range scales is discussed in connection with the dielectric properties of these materials.