Relaxation mode in0.65Pb(Mg1/3Nb2/3)O3−0.35PbTiO3relaxor single crystals studied by micro-Brillouin scattering

Abstract

Relaxor ferroelectric single crystals ${0.65\mathrm{P}\mathrm{b}(\mathrm{M}\mathrm{g}}_{1/3}{\mathrm{Nb}}_{2/3}{)\mathrm{O}}_{3}{\ensuremath{-}0.35\mathrm{PbTiO}}_{3}$ have been studied in detail by high resolution micro-Brillouin scattering technique over a wide temperature range (-190--600 \ifmmode^\circ\else\textdegree\fi{}C) in microareas with a size of 1--2 \ensuremath{\mu}m. One phase transition from cubic to tetragonal at ${T}_{C\ensuremath{-}T}\ensuremath{\sim}158\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ has been clearly observed, and the other from tetragonal to rhombohedral near 60 \ifmmode^\circ\else\textdegree\fi{}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 ${T}_{C\ensuremath{-}T}+80\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and shows marked temperature dependence above ${T}_{C\ensuremath{-}T}.$ Below ${T}_{C\ensuremath{-}T},$ its intensity decreases gradually, but exists down to -130 \ifmmode^\circ\else\textdegree\fi{}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 ${T}_{P}\ensuremath{\sim}852\mathrm{K}$ corresponding to the appearance of precursor microregions was obtained. The validity of the semiclassical tunneling model was also discussed.