Elastic Constants and Quasi-elastic Central Peaks of Ferroelectric Lead Barium Niobate Single Crystals Studied by Brillouin Spectroscopy

The elastic constants of tetragonal tungsten-bronze lead barium niobate, Pb(1−x) BaxNb2O6 with x = 0.5, were determined under poled and unpoled conditions by using Brillouin spectroscopy. The elastic constant C11 was larger than C33 similar to other ferroelectric tungsten-bronze systems. The C11 did not show any appreciable change between the poled and unpoled conditions while the C33 increased from 117 to 173 GPa upon poling the sample. This substantial change was attributed to the higher density of domain walls and the polar nanoregions in the unpoled condition and the resulting strong coupling between the longitudinal acoustic waves propagating along the polar c-axis and the one-dimensional order parameter aligned along the same direction. This elastic anisotropy associated with the dimensionality affected the acoustic damping and the central peak behaviors.