On the existence of the relaxation mode in relaxor ferroelectrics

The lattice dynamics of PbMg1/3Nb2/3O3 and PbMg1/3Ta2/3O3 relaxor ferroelectrics is investigated by inelastic neutron scattering. The relaxation mode in these crystals is revealed from an analysis of the low-frequency part of the vibrational spectrum. The possible reasons for the appearance of this mode are discussed, and different approaches to the description of the low-frequency spectrum of ferroelectrics are compared.