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

Abstract

Intensity and shift of the Brillouin scattering due to the longitudinal acoustic phonons in NH₄LiSO₄ 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(T₀−T)⁻¹ sec.