Brillouin scattering study of the ferroelectric phase transition in tris-sarcosine calcium chloride.

Abstract

Brillouin spectra from longitudinal phonons in ferroelectric tris-sarcosine calcium chloride propagating along [100], [010], and [001] have been measured as functions of temperature. Large anomalies were found in the Brillouin shift and linewidth in the [100] and [001] phonons. These anomalies are interpreted as arising from the linear coupling of the polarization and the phonons. From the temperature where the linewidth is maximum, the relaxation time of the polarization fluctuations is estimated to be \ensuremath{\tau}=3.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$/(${T}_{c}$-T) sec, where ${T}_{c}$ is the ferroelectric transition temperature. We also observed anomalies in Brillouin shift and linewidth of the [010] phonons which propagate along the ferroelectric b axis. These anomalies are interpreted as coming from electro- strictive coupling. The energy-relaxation time was estimated to be ${\ensuremath{\tau}}_{E}$=2.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$/(T-${T}_{c}$) sec in the paraelectric phase and ${\ensuremath{\tau}}_{E}$=1.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$/(${T}_{c}$-T) sec in the ferroelectric phase, by comparing our Brillouin results with those of the ultrasonic measurements.