Nonlinearity of strain and strain hysteresis in morphotropic LaSr-doped lead zirconate titanate under unipolar cycling with high electric fields

The strain behavior of morphotropic, 1La2Sr-doped lead zirconate titanate was investigated. Particular attention was paid to the electric field induced strain (S-E characteristic) in the high field range for morphotropic materials having different Zr/Ti ratios. Unipolar electrical cycles with maximum fields between 1 and 3 kV/mm were applied to the poled materials under load-free conditions. Strain curves were recorded and the data were evaluated with respect to field dependence of strain and strain hysteresis. Nonlinearity of strain was detected for all materials. Depending on the composition, marked differences were found with respect to the types of nonlinearity. The corresponding data on strain hysteresis indicate that the nonlinearity was due to a loss generating strain mechanism. Therefore the nonlinearity was attributed to domain switching. A phenomenological model is suggested, which is based on the assumptions of a distribution of domain switching over a field range. This field range is characterized by the activation field parameter E-a, which is specific for each composition. The model is capable of explaining the types of nonlinearity in strain that have been observed.(c) 2007 American Institute of Physics.