Elastic behavior and dynamical aspects of polarization in Pb(Mg1/3Nb2/3)O3and Pb(Mg1/3Ta2/3)O3studied by Brillouin spectroscopy

Abstract

Brillouin light scattering studies of the elastic behavior and central peak have been reported for prototype relaxors Pb(Mg1/3Nb2/3)O3 and Pb(Mg1/3Ta2/3)O3 in the temperature range 873–100 K. The elastic constant C11 corresponding to longitudinal acoustic phonon mode exhibits a broad minimum followed by a broad maximum in attenuation at Tm. The temperature dependence of C11 above Tm has been analyzed using a simple mean field model. The analysis shows that below the characteristic temperature T* = To + 40 K, C11 deviates from the mean field behavior. Attenuation also shows a rise at this temperature. The deviation of C11 from the mean field behavior is attributed to the strong coupling between the local polarization and strain and is qualitatively discussed in terms of Edwards-Anderson parameter qEA. The intermediate temperature T* obtained in the present study is found to be consistent with reported X-ray, Raman and acoustic emission studies. Broad central peak that begin to appear below T* shows decrease in width and increase in intensity with decrease in temperature. For both PMN and PMT, the relaxation time of central peak exhibits critical slowing down with an anomalous change below the freezing temperature Tf. The temperature dependence of relaxation time of the central peak exhibits a non-Arrhenius behavior. The possible origin of relaxation mechanisms for the observed critical slowing down between T* and Tf and below Tf is qualitatively discussed.