Anomalous behavior of the phonon spectrum of the relaxor ferroelectric PMNat low temperatures

The density of states (DOS) has been measured in powdered Pb(Mg1/3Nb2/3)O-3 (PMN) by inelastic neutron scattering in the temperature range from 300 K to 50 K. The one-phonon approximation was used to calculate the DOS from me asured spectra. The data analysis shows that the temperature dependence of the DOS exhibits some anomalous features in the vicinity of the electric-fi eld-induced Ferroelectric transition at about 200 K. We could describe the vibrational spectrum according to Fm3m symmetry, and thus obtained an argum ent in favor of this model of PMN structure. In the present work we discuss the nature of anomalies in the temperature dependence of the DOS in PMN an d obvious correlations in the behavior of phonons in PMN that were revealed by different methods (neutron, Brillouin and Raman scattering).