Relaxation mode in 0.65Pb(MgU1/3Nbu2/3)O3-0.35PbTiO3 relaxor single crystals studied by micro-Brillouin scattering

Relaxer ferroelectric single crystals 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) have been studied in detail by high resolution micro-Brillouin scattering technique over a wide temperature range (-190-600 degrees C) in microareas with a size of 1-2 mu m. One phase transition from cubic to tetragonal at T(C-T)similar to 158 degrees C has been clearly observed, and the other from tetragonal to rhombohedral near 60 degrees C with uncertainty, upon cooling through both the frequency shift and hypersonic damping. The change of Brillouin shift indicates that the former transition is the first order, while the latter is diffusive. In addition, a relaxation mode has been clearly observed as a broad Rayleigh wing; it appears at about TC-T+80 degrees C and shows marked temperature dependence above TC-T. Below TC-T, its intensity decreases gradually, but exists down to -130 degrees C. By fitting the Rayleigh wing, the relaxation time was obtained as a function of temperature. A modified superparaelectric model was developed to describe the relaxation mode, a reasonable characteristic temperature T(P)similar to 852 K corresponding to the appearance of precursor microregions was obtained. The validity of the semiclassical tunneling model was also discussed.