Non-linear piezoelectric response in lead zirconate-titanate (PZT) films

The effect of the ac electric field on piezoelectric properties is investigated in lead zirconate-titanate (PZT) films of various compositions and thicknesses. Non-linear piezoelectric properties of PZT films are compared to those of bulk ceramics. It is shown that non-linearity is strongly suppressed in thin films of the submicron thickness whereas thick films (7-8 mu m) demonstrate relatively strong non-linearity comparable to that of "hard" PZT ceramics. Non-linearity in thick films is described by the empirical expression d=d(lin)[1+(d(nl)E)(alpha)] with alpha approximate to 1.2, Tetragonal films with <111> texture show almost field-independent piezoelectric response due to the reduced contribution of 90 degrees domains. The piezoelectric coefficient obeys logarithmic-type frequency dependence. The frequency dispersion increases with ac-field and can be related to the relaxation of non-180 degrees domains. The results provide direct experimental evidence of the domain wall motion contribution to the piezoelectric properties of PZT films.