Anomalous transverse acoustic phonon broadening in the relaxor ferroelectric Pb (Mg1/3Nb2/3)0.8Ti0.2O3

The intrinsic linewidth Γ T A of the transverse acoustic phonon observed in the relaxor ferroelectric compound Pb(Mg 1 / 3 Nb 2 / 3 ) 0 . 8 Ti 0 . 2 O 3 (PMN-20%PT) begins to broaden with decreasing temperature around 650 K, nearly 300 K above the ferroelectric transition temperature T c (∼360 K). We speculate that this anomalous behavior is directly related to the condensation of polarized, nanometer-sized, regions (PNR) at the Burns temperature T d . We also observe the "waterfall" anomaly previously seen in pure PMN, in which the transverse optic branch appears to drop precipitously into the TA branch at a finite momentum transfer q w f ∼0.15 A - 1 . The waterfall feature is seen even at temperatures above T d . This latter result suggests that the PNR exist as dynamic entities above T d .