Dispersion of hypersonic velocity and damping at diffuse phase transition in PbMg_1/3Nb_2/3O₃

Abstract

Dispersion of the acoustic anomalies for hypersonic phonons studied by Brillouin scattering has been found in region of a typical diffuse ferroelectric phase transition in PbMg_1/3Nb_2/30₃ Both the velocity dip and the damping maximum centred on the mean Curie temperature are connected with fluctuation contributions. The value of anomalies is decreased by dispersion at high frequencies. The relaxation contribution dispersion leads to the appearing of an ordinary shifted maximum of damping and the stretching of velocity step when measuring at Brillouin frequencies.