IMF2017

(Na_1/2Bi_1/2)TiO₃ (NBT) belongs to relaxor ferroelectrics with disorder in the perovskite A-sublattice. Investigations of the NBT structure and physical properties have not succeeded in obtaining a complete picture of the crystal lattice dynamics. Only the structural phase transition of its cubic phase into a tetragonal ferroelastic one near 813 K and the ferroelectric state below 560 K have been established. The behaviors of the dielectric response in the "isotropization" region (620-580 K) and acoustic phonons in the vicinity of the ferroelectric state onset in NBT are intriguing. This report presents investigations of the dielectric response, conductivity, domain structure, and low-frequency region of the vibrational spectrum of NBT single crystals in the temperature range 290-750 K for the [100], [110], and [111] crystallographic directions. It is shown that the temperature evolution of the domains arising at T < 800 K has a temperature region 620-540 K in which domains disappear completely ([100] and [111] directions) or partially ([110] direction). This isotropization region manifests itself in the behavior of the imaginary part of the dielectric response and is due to the isotropic nature of conductivity. As Brillouin scattering experiments showed, the ferroelectric state onset was accompanied by softening of longitudinal and transverse acoustic phonons. Analysis of the NBT light scattering spectra revealed multicomponent quasielastic scattering. Temperature dependences of relaxation time and susceptibility the anomalous behaviors of which correlated with the anomalies in the behaviors of velocity and susceptibility of long-wavelength acoustic phonons were plotted.