Respuesta extrínseca y comportamiento no lineal en materiales cerámicos piezoeléctricos

Abstract

The study of the elastic, dielectric and piezoelectric non-linear behavior in PZT-based and KNN-based piezoelectric ceramics represent the main goal of this work. Both systems present a perovskite-like structure. Several experimental set-ups were designed, mounted and automated to be used in this study. First, the elastic non-linear response, in resonance, is measured. The purpose is to study the variation of the elastic coefficient of the material when it is submitted to high stress. A model is formulated based on the variation of the coefficients due to the increase in amplitude of the high stress applied. The correspondence between the model and the experimental observations is verified. The results show a good agreement in soft PZT case but not in hard PZT, confirming that is not possible to assume a non-linear -like dependence for hard PZT coefficients. Secondly, we take a view of the dielectric, piezoelectric and elastic response over the temperature. The purpose of the study is to evaluate the contribution of the extrinsic effect to piezoceramics response. Anomalous behavior of the macroscopic properties of the hard PZT around the Room Temperature is observed. A preliminary model is proposed to explain such behavior. The contribution of the extrinsic effect to the macroscopic properties in a KNN compound is evaluated and the results suggest that the anomaly observed around Room Temperature would be associated, in this case, with the presence of a structural transition between two ferroelectric phases. Temperature dependent non-linear dielectric response is also observed. The study was carried out by measuring the dielectric permittivity at low frequencies and at high applied electric fields in a temperature range from 20K till 400K. The results have been analyzed using the Rayleigh model. The change in the hard PZT dynamic walls is shown and explained through an intuitive model. The results obtained in the KNN system display a soft PZT like behavior at Room Temperature. Nevertheless, the anomaly observed in the dielectric proper ties around Room Temperature was associated to the above mentioned structural transition between two ferroelectric phases. Finally, temperature dependent mechanical non-linear response in soft PZT ceramics is studied. The variations of the coefficients with the stress and with the temperature are studied and the similarities between the linear and non-linear regime are assessed. It is observed that the change of the extrinsic contribution with the temperature is qualitatively similar that the variation observed by the application of the high mechanical stress, thus indicating that the effect is due to a common phenomenon.