The low frequency dynamics in c-cut crystal and ADP doped-KDP crystal were studied under square pulses employing the Bark-hausen type experimental technique.
The piezoelectric coupling of $P_z$ with acoustic shear mode oscillation and electrostrictive coupling of $P_z$ with the thickness vibration along z-direction were found to be strongly coupled to the homogeneous polarization fluctuation of both pure KDP and ADP doped-KDP crystal.
The dielectric anomaly associated with the c-axis spontaneous polarization was observed occuring at lower temperature as the ADP impurity concentration was increased.
We also observed the polarization reversal current and measured switching time as a function of applied field below $T_c$, where we found that the peak current increased while the switching time remained constant as the applied field was increased.
