Ultrasonic Study near the Ferroelectric Phase Transition of RbHSO4

The anomalous ultrasonic attenuation and velocity of the longitudinal wave propagating along the b -axis perpendicular to the ferroelectric axis ( c -axis) of RbHSO 4 have been measured as functions of temperature and frequency near the transition temperature T C . By assuming the single relaxation process of the fluctuation induced by the ultrasonic wave at each temperature, the relaxation time τ has been analyzed. Above T C thus obtained relaxation time indicates a cross-over behavior in which the relaxation time has the exponent of n ≈0.3 for T - T C <0.2^° C and the exponent of n ≈2 for T - T C >0.2^° C . The former and the latter relaxation processes seem to be related to the energy and the polarization relaxation processes, respectively. The similar cross-over behavior has been obtained below T C .