Hypersound anomalies and elastic constants in single-crystal PbMg1/3Nb2/3O3 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 θ s =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 θ s =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 T c ∼212 K. This anomaly implies a rapid growth of ferroelectric ordering near T c and is consistent with the earlier linear birefringence results reported by Westphal et al. The elastic stiffness and compliance constants, C E 11, C E 44, and s E 44 are also determined between 200 and 370 K.