Raman scattering study of the soft mode in Pb(Mg1/3Nb2/3)O3

Systematic Raman scattering experiments were performed on Pb(Mg1/3Nb2/3)O-3 (PMN) single crystals to resolve the low-wavenumber dynamics in the crystal. Careful checking of the angular dependence of the Raman spectra indicated that the intense peak around 45 cm(-1), which always smears the low-wavenumber spectra, stems from the F-2g mode due to Mg : Nb = 1 : 1 chemically ordered Fm (3) over barm region. A proper scattering configuration for eliminating the strong F-2g mode allowed the observation of the lowest wavenumber soft mode dynamics in PMN. The results revealed the softening of the mode towards T-c with underdamped oscillation. The soft mode becomes overdamped in a wide temperature range above T-c, suggesting the development of cluster dynamics due to polar nanoregions. It recovers the underdamped oscillation and hardens in the high-temperature region. Finally, the physical picture of the relaxor phenomenon in PMN is discussed in terms of lattice dynamics by comparison with the typical displacive-type ferroelectric phase transition. Copyright (C) 2010 John Wiley & Sons, Ltd.