ABSTRACTThe piezoelectric and dielectric properties of ferroelectric thin films and ceramics were investigated in detail as a function of the frequency and amplitude of the driving field. A description, which is based on the theories of domain wall pinning by randomly distributed imperfections in magnetic materials, is used to interpret the electromechanical behaviour of several ferroelectric bulk ceramic and thin film compositions. With this approach, it is possible to make quantitative estimates of the domain wall contributions to the electromechanical properties of ferroelectric sensors and actuators.