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 powde r and single crystals. The structure of PSN is discussed and compared with those of simple perovskite compounds BaTiO3 and PbTiO3. In PSN th e 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 s cales is discussed in connection with the dielectric properties of the se materials.