Anomalous Temperature Dependence of the Intensity of Brillouin Scattering near the Ferroelectric Phase Transition Point of NH4LiSO4

Intensity and shift of the Brillouin scattering due to the longitudinal acoustic phonons in NH 4 LiSO 4 were measured precisely as functions of temperature near the ferroelectric phase transition point ( T c =186.5°C). Anomalous decrease of the peak intensity was observed around several degrees below T c . This behaviour is interpreted in terms of the conventional Landau-Khalatnikov theory of critical relaxation. The relaxation time of the order parameter thus obtained is (0.9±0.1)×10 -10 ( T 0 - T ) -1 sec.