Broadband gigahertz dynamics of relaxor ferroelectric Pb(Sc1/2Nb1/2)O3-xPbTiO3 single crystal probed by Brillouin scattering

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The broadband gigahertz dynamics of a relaxor ferroelectric crystal 0.70Pb(Sc1/2Nb1/2)O3-0.30PbTiO3 with a composition close to the starting point of the morphotropic phase boundary is studied by Brillouin scattering. The significant anomaly of the longitudinal acoustic (LA) mode is observed in the vicinity of the Curie temperature, TC = 500 K. Upon cooling, it starts below the Burns temperature, TB = 670 K, due to the interaction between the LA mode and dynamic polar nanoregions (PNRs). The broad central peak (CP) clearly appears below TB, and its intensity becomes a maximum at TC. The relaxation time, τCP, determined from the CP width, shows the typical critical slowing down of the order-disorder phase transition in the vicinity of TC. The size of a dynamic PNR significantly increases below the intermediate temperature, T* = 562 K.