Comparison of Acoustic Behaviors Between the Perovskite and the Tungsten-Bronze Uniaxial Relaxors.

The longitudinal acoustic mode behaviors of three cubic perovskite relaxors and one tungsten-bronze uniaxial relaxor were compared in a widest temperature range by Brillouin scattering. All investigated relaxors exhibited substantial softening of the Brillouin shift upon cooling and a sudden increase in the hypersonic damping at a temperature lower than the Burns temperature, from which four characteristic temperatures were defined in relation to the temperature evolution of polar nanoregions. The Brillouin shift of the uniaxial Sr0.61Ba0.39Nb2O6 relaxor showed a positive slope at temperatures above the Burns temperature, which indicates the existence of coupling between some persisting relaxation process and the acoustic waves propagating along the polar axis. [ABSTRACT FROM AUTHOR]