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

TL;DR

This study uses Brillouin scattering to investigate phonon anomalies and central peak behavior in PZN-PT single crystals, revealing critical dynamics and phase transition characteristics related to relaxor ferroelectricity.

Contribution

It provides new insights into phonon softening, central peak dynamics, and phase transition mechanisms in PZN-PT using temperature-dependent Brillouin spectroscopy.

Findings

LA phonon softening below 650 K at Burns temperature

Anomaly in LA mode frequency and linewidth around 463 K

Critical slowing down of the central peak near T* indicating order-disorder transition

Abstract

Brillouin spectroscopic measurements have been carried out on relaxor ferroelectric Pb(Zn1/3Nb2/3)0.85Ti0.15O3 (PZN-PT) single crystal over the temperature range 300-585 K. The longitudinal acoustic phonon begins to soften below 650 K, which is attributed to the Burns temperature (TB). On the other hand, the line width of the longitudinal acoustic (LA) phonon mode exhibits a sharp Landau-Khalatnikov-like maximum and an accompanying anomaly in the LA mode frequency around 463 K, the tetragonal-cubic phase transition temperature (Ttc). In addition, a broad central peak, found below the characteristic intermediate temperature T* ~ 525 K, exhibits critical slowing down upon approaching Ttc indicating an order-disorder nature of the phase transition. The relaxation time of polar nano regions estimated from the broad central peak is found to be same as that obtained for LA phonon mode suggesting an electrostrictive coupling between strain and polarization fluctuations. The activation energy for the PNRs relaxation-dynamics is found to be ~236 meV. Polarized nature of the central peak suggests that the polar nano regions have the tendency to form long-range polar ordering.