Order-disorder behavior of ferroelectric phase transition of KTa1-xNbxO3 probed by Brillouin scattering

The precursor dynamics of a cubic-tetragonal ferroelectric phase transition of potassium tantalate niobate (KTa1-xNbxO3 with x = 0.32) crystals is studied by Brillouin scattering. The appearance of the central peak (CP) and marked softening of the elastic constant c(11) are clearly observed above the Curie temperature, TC-T, owing to the interaction between the LA mode and local polarization fluctuations of polar nanoregions (PNRs). The relaxation time determined by the CP width clearly shows a critical slowing down above TC-T, indicating an order-disorder feature of the ferroelectric phase transition. The size of a dynamic PNR is evaluated, and it increases toward TC-T. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560345]