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



Systematic Raman scattering experiments were performed on Pb(Mg1/3Nb2/3)O3 (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 F2g mode due to Mg:Nb = 1:1 chemically ordered Fm3m region. A proper scattering configuration for eliminating the strong F2g mode allowed the observation of the lowest wavenumber soft mode dynamics in PMN. The results revealed the softening of the mode towards Tc with underdamped oscillation. The soft mode becomes overdamped in a wide temperature range above Tc, 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 © 2010 John Wiley & Sons, Ltd.