Broadband light scattering of two relaxation processes in relaxor ferroelectric 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 single crystals

Dynamical properties of relaxor ferroelectric 0.93Pb(Zn1/3Nb2/3)O-3-0.07PbTiO(3) single crystals have been studied by the broadband inelastic light scattering from gigahertz to terahertz frequency range. The longitudinal- and transverse-acoustic (LA and TA) phonon frequencies deviate below the Burns temperature T-B=736 K from a linear temperature dependence above T-B, indicating the existence of polarization relaxations induced by the polar nanoregions (PNRs). On further cooling, a central peak (CP) which originates from the relaxations in the PNRs is observed clearly below 600 K < T-B. The CP width decreases markedly down to T-*=499 K and the change in the CP width becomes mild below T-*. The slower (similar to 10(-12) s) and faster (similar to 10(-13) s) relaxation times determined by the CP show good agreement with the relaxation times determined by TA and LA phonons, respectively. 180 degrees and non-180 degrees (71 degrees and 109 degrees) polarization flippings are allowed in the PNRs with the polar rhombohedral symmetry. Considering the piezoelectric coupling in a PNR, it is suggested that 180 degrees flipping is related to the relaxation observed in LA phonon, while non-180 degrees flipping is related to that in TA phonon.