Polarized Raman study of the phonon dynamics in Pb(Mg1/3Nb2/3)O3 crystal -: art. no. 104107

Pb(Mg1/3Nb2/3)O-3 is one of the simplest members of the class of lead relaxors and often serves as a model system for more complicated compounds. In this paper, we analyze both polarized and depolarized Raman-scattering spectra, measured in the temperature range between 1000 and 100 K, using a multiple-peak decomposition. Based on this analysis, we propose a comprehensive picture of the structural transformations in the crystal and associated dynamics. According to our model, the formation of the Fm (3) over barm symmetry in the chemically ordered regions as well as the appearance and freezing of the polar nanoregions are the consequences of the same phenomenon: the off-centered displacements of ions and their fast reorientational thermal motion. Short-lived dynamic lattice distortions are present even at the highest measured temperatures. From the Burns temperature, T(d)similar to620 K, their motion becomes progressively more restricted. Temperature T(*)similar to350 K marks the beginning of the freezing process which continues down to the temperature of the electric-field-induced phase transition, T(d0)similar to210 K. Raman scattering exists due to the presence of local lattice distortions. It is characterized by phonons with different wave vectors interacting with dynamic and static disorder.