A simple and reliable method which allows one to distinguish between the two major microscopic scenarios for the suppression of the switching polarization (P-r(s)), i.e., pinning of ferroelectric domain walls (DWs) through the Pb(Zr,Ti)O-3 film (PZT) (bulk scenario) and inhibition of the growth of opposite domains due to the nucleus suppression at the electrode interfaces (interface scenario), is proposed. In addition, a new electric treatment able to significantly suppress P-r(s) in Pt-PZT-Pt ferroelectric capacitors (FECAPs) of thicknesses above 1.4 mu m, was discovered and studied. It consists of the application of an external alternating electric field (E-e) which cycles the polarization at very low frequency (1.7 mHz). After only 10-20 cycles, P-r(s) can be suppressed by a factor of 10. The same FECAP, when subjected to E-e at higher frequency (30 kHz), endures at least 10(8) switches, before attaining an equivalent P-r(s), suppression (hereafter called fatigue). The fatigued states obtained with the two different procedures appear to be different. In the first case (slow cycling) it is suggested that the suppression of P-r(s) is related to the DW pinning scenario, whereas in the second case-which corresponds to the normal fatiguing procedure-it is related to the interface scenario. (C) 1998 American Institute of Physics. [S0003-6951(98)01619-2].