Strain mechanisms in lead-free piezoelectric BNT-BT under the influence of an applied electric field

Full text: Due to the rapidly increasing amount of electrical and electronic waste, the EU parliament adopted several legislations in order to protect human health and the environment from toxic substances. Lead containing substances used in piezoelectrics are solely allowed in the EU, because there is not yet a broadly appropriate substitute available. One of the most promising material for piezoelectric actuator applications is the solid solution Bi_0.5Na_0.5TiO₃-BaTiO₃ (BNT-BT). Beside the composition with 6–7 % BT, the BT-rich side also shows a remarkably high piezoelectric coefficient and large electric field induced strain response. The high electric field induced strain mechanisms of piezoceramics were considered as follows: lattice strain (intrinsic effect), switching of ferroelectric domains (extrinsic effect) and phase transitions. To analyze and quantify all these effects in strain mechanisms in 12 % BT, we developed a method with Strain, Texture, and Rietveld Analysis for Piezoceramics (STRAP) acquired from data using in situ X-ray powder diffraction. That allows a precise insight into the structural process of switching between the poled and the remanent state. Additionally, the experiments were carried out with several frequencies of the applied field using different setups. In order to correlate the results based on atomic scale with the macroscopic observations, electromechanical measurements were performed. The results jointly substantially contribute to the development of novel promising lead-free piezoceramics. (author)