Hypersound anomalies and elastic constants in single-crystal PbMg 1/3Nb2/3O3 by Brillouin scattering

Abstract

The longitudinal (LA) and transverse (TA) Brillouin spectra along [001] phonon direction have been measured as a function of temperature (50-475 K) in single-crystal PbMg1/3Nb2/3O3 with scattering angles θs=180°and 32.5±0.2°. The Brillouin frequency shift with decreasing temperature shows a broad softening anomaly for both LA and TA phonon modes. For θs=180°, a gradual growth in damping with maximum near 270 K is observed and is attributed to order parameter fluctuations. An additional Landau-Khalatnikov maximum is also observed at Tc∼212 K. This anomaly implies a rapid growth of ferroelectric ordering near Tc and is consistent with the earlier linear birefringence results reported by Westphal et al. The elastic stiffness and compliance constants, CE11, CE44, and sE44 are also determined between 200 and 370 K. © 1995 American Institute of Physics.