Anomalous behavior of acoustic phonon mode and central peak in Pb(Zn1/3Nb2/3)0.85Ti0.15O3 single crystal studied using Brillouin scattering

Abstract

Brillouin spectroscopic measurements have been carried out on relaxor ferroelectric Pb(Zn1/3Nb2/3)0.85Ti0.15O3 single crystal over the temperature range 300–873 K. The frequency of longitudinal acoustic phonon (LA) begins to exhibit a strong decrease below the Burn's temperature TB followed by an increase in the line-width below the characteristic intermediate temperature T* ∼ 525 K. The line-width of the LA phonon mode exhibits a sharp Landau-Khalatnikov-like maximum at 463 K, the tetragonal-cubic phase transition temperature (Ttc). In addition, a broad central peak, found below T* exhibits critical slowing down upon approaching Ttc indicating an order-disorder nature of the phase transition. The relaxation time of polar nanoregions estimated from the broad central peak is found to be same as that obtained from LA phonon mode suggesting a strong coupling between strain and polarization fluctuations.