Critical slowing down of relaxation dynamics near the Curie temperature in the relaxor Pb (Sc_0.5 Nb_0.5) O₃

Brillouin spectroscopy of Pb (Sc_0.5 Nb_0.5) O3 single crystals reveals an order-disorder ferroelectric phase transition occurs at 110 °C upon cooling. A softening of the longitudinal acoustic (LA) mode is observed that can be attributed to the coupling between polar nanoregions and acoustic modes. A critical slowing down of the central peak, a feature of order-disorder ferroelectric phase transitions, is observed near Tc. The similarity in temperature dependences of the two kinds of relaxation times determined from the central peak and LA mode suggests that the changes in the central peak arise from local polarization fluctuations in the polar nanoregions.