Novel piezoelectric compositions for advanced electronics
Conventional PZT materials have been found potentially insufficient to cover the needs of modern actuator applications. Such devices have high requirements on piezoelectric and electromechanical coupling coefficients, as well as on dielectric permittivity. To answer this need the PIRAMID project extensively investigated a variety of relaxor-ferroelectric solid solutions and focused on improving their properties. By adopting novel powder processing techniques, researchers used new methods for preparation of textured ceramics. One of the key project results includes innovative piezoelectric compositions, the relaxor-based Pb[(Ni_1/3 Nb_2/3)_x Zr_y Ti_1-x-y ]O_3 system, commonly PNNZT. This novelty features very high permittivity and coupling, while dielectric and mechanical losses have been reduced by doping. The PNNZT is ideal for applications where a unique combination of the traditional soft and hard PZT properties is required. Thereby, its high permittivity is suitable for electrical impedance matching and its high sensitivity for good efficiency or signal/noise ratio. Additionally, the low dielectric and mechanical losses displayed can make this material the perfect candidate for high-power operation applications. Key application fields of the PNNZT materials include high-intensity focused ultrasound, underwater acoustics and medical diagnostics. The new material is already under commercialisation with the type number Pz54. The PIRAMID project also investigated the possibilities of developing low-lead content and lead-free materials. This was achieved by replacing lead by the less toxic bismuth resulting to eco-friendlier compositions than conventional PZTs. As such, the new system of the general form of BiMe-PT is a solid solution between BiMeO3 and PbTiO3. The BiMe-PT compositions have been developed in such a way that the cost of precursors was kept minimum in order to end up in low-priced compositions. These display very interesting properties, such as high piezoelectric coefficients, free relative permittivity and thickness coupling factor. One of the BiMe-PT compositions features a very high Curie point that is limited by the operating temperature, which is a restricting factor for its further exploitation. However, it is expected that future work with dopants will allow overcoming this drawback resulting to a new material filling in the gap between PZT and the Aurivillius compounds (Bi layer oxides).
