ANISOTROPIC THERMAL RELAXATION DYNAMICS IN TGS STUDIED BY IMPULSIVE STIMULATED LIGHT-SCATTERING

An ultraslow relaxational mode with a relaxation time tau = 5 similar to 8 mu sec is discovered for the first time near the phase transition temperature T-c = 48.5 degrees C in uniaxial ferroelectric triglycine sulfate (NH2CH2COOH)(3) . H2SO4 using time-resolved spectroscopy. The physical origin of the mode is assigned to he thermal relaxation, bec ause dominant anisotropic anomalous behavior can be observed in the Br agg-diffracted mode intensity at time origin I(0) and can he well expl ained by the anisotropic anomaly of the thermal expansion coefficient alpha and the anomaly of the specific heat at constant stress C-X. The thermal diffusivity D-th evaluated from tau also shows the anisotropi c anomalous behavior. This behavior is successfully interpreted by the anisotropic polarization fluctuation characteristic of the structural phase transitions of uniaxial ferroelectrics.