A phenomenological approach is proposed describing both nonlinearity and frequency dispersion in dielectric and piezoelectric properties of lead zirconate titanate, Pb(Zr,Ti)O-3 (PZT), thin films and ceramics. The approach couples the frequency dependent response in form of the power law, 1/omega(beta), with the rate-independent nonlinear response described by the Rayleigh law. The main experimental trends are well described by the model. (c) 2005 Elsevier B.V. All rights reserved.