Ferroelectric phase transition inRbH2PO4: Picosecond time-resolved impulsive stimulated Brillouin scattering experiments

Abstract

The anomalous acoustic behavior of rubidium dihydrogen phosphate near its ferroelectric phase transition was studied using ‘‘impulsive’’ stimulated Brillouin scattering with several scattering angles between 5.05° and 32.2°. The $C_{66}$ shear elastic stiffness constant in the high-temperature phase showed elastic Curie-Weiss behavior, as expected on the basis of mean-field (MF) theory of the phase transition. Logarithmic corrections to MF behavior, suggested by other reports, were not observed to within 0.01 K of $T_c$. The $p_{66}$ photoelastic constant also showed MF behavior. The polarization relaxation-time divergence was consistent with Landau-Khalatnikov theory, i.e., τ∼(T-$T_0$ ${)}^{\mathrm{-}1}$ over a substantial temperature range. Our observations are in agreement with those made on other KDP-family crystals, and with theoretical expectations for uniaxial ferroelectrics which are also ferroelastic in the low-temperature phase.