The Increase in Permittivity of Ferroelectrics as a Consequence of the Polarization Reversal Process. Part I. Experimental Data

The small-signal complex permittivity of ferroelectric barium titanate and triglycin sulphate single crystals in the frequency range 100 kc/ s to 2 Mc/ s was measured, during the polarization reversal process excited by rectangular pulse field. During the switching pulse, both the components of the complex permittivity have anomalously large values. The time dependence of the imaginary part of the complex permittivity has roughly the same shape as the switching current curve, while the real part lags considerably behind and reaches its maximum value at a later time. The frequency dependences of the complex permittivity measured on the rising part of the switching current differ in shape from those measured on the falling part. None of these frequency dependences is a simple Debye relaxation, not even in barium titanate. A possible explanation of the increase in complex permittivity during switching on the basis of the nucleation model of switching is suggested, in which the nucleation probability is modulated by the weak alternating field.