Dielectric and Brillouin scattering anomalies in an Na12/Bi12/TiO3 (NBT) relaxor ferroelectric crystal

We investigated dielectric and hypersonic properties of NBT over a wide temperature range. The dielectric permittivity and loss measured from 20 Hz to 300 kHz agree at lower temperature with previous results. At higher temperature in and near the tetragonal phase the lower frequencies show a very large permittivity peak with considerable dispersion and large loss. This behavior is very similar to that found in other perovskite crystals and ceramics, in some cases far above T_c. We attribute it to extrinsic bulk conductivity. The phase shift giving nonzero σ" in σ=σ\´+jσ" may be caused by a spread in mobility activation energy. The Brillouin scattering data at 514.5 nm show a very broad dip in sound velocity and a very large and broad attenuation peak, both centered in the tetragonal phase temperature range. This behavior is attributed to hybridization of order parameter and cluster fluctuation contributions.