Brillouin Scattering Studies of Dynamics of Polar Nanoregions in Pb[(In1/2Nb1/2)0.65Ti0.35]O3 Single Crystals.

The dynamical properties of polar nanoregions have been investigated in Pb[(In_1/2Nb_1/2)_0.65Ti_0.35]O₃ single crystals by Brillouin scattering. Longitudinal acoustic phonons begin to show softening below the Burns temperature T_B∼700 K. The Brillouin shift in the longitudinal acoustic phonon mode exhibits clear anomalies at the cubic–tetragonal phase transition temperature of around T_ct∼550 K and at the tetragonal–rhombohedral one of around T_tr∼460 K. Broad and narrow central peaks begin to appear below T_B and the intermediate temperature T^*∼600 K, respectively. Relaxation rate was calculated in the longitudinal phonon mode and central peaks. Below T^*, the relaxation rate calculated from the longitudinal phonon mode agrees well with that of the broad central peak, suggesting the coupling between local polarization and strain fluctuations due to the formation of long-lived polar nanoregions. The polarization of the central peaks in the cubic phase suggests that polar nanoregions have the tendency to form long-range polar ordering. [ABSTRACT FROM AUTHOR]