Study on the Ultrasonic Relaxation Just above the Transition Temperature of Triglycine Sulfate

The velocity and the attenuation coefficient of the longitudinal ultrasonic wave propagating along the ferroelectric b axis of triglycine sulfate (TGS) have been measured as a function of temperature in the paraelectric phase. The effective relaxation time τ eff was evaluated as a function of temperature from these data. A value of the τ eff is 0.95×10 -11 sec at T – T c =1.00°C. The temperature dependence of τ eff cannot be understood only by the energy relaxation mechanism, and suggests a possibility of another process through two polarization relaxation modes discussed by the mode-mode coupling theory.