Sustainable development of high sensitivity piezoelectric ceramics in the BCZT system for applications in bio-devices

Recent EU policies adopted to foster the ecological transition have led to a growing and fervent interest in the search for new environmentally friendly materials and processing routes. In this regard, one of the most effervescent fields concerns the development of multifunctional lead-free electro-ceramics as main components of key technological devices. One of the main challenges is to replace the market-dominant but toxic lead zirconate titanate. Considering the problems of supply of so-called 'critical raw materials', human health and the environment, a promising alternative is represented by the pseudo-ternary system barium-calcium-zirconate-titanate (BCZT). Since the publication of the seminal work by Liu and Ren, this lead-free option has attracted the interest of researchers due to the exceptional piezoelectric properties (d33=620 pC/N) shown by a particular composition. However, some open issues still represent a tangible problem for technology transfer, including the search for energy-efficient and scalable solid-state water-based processing routes, as well as available routes to ensure the reproducibility of final properties. In this Thesis, the processing temperatures were significantly reduced by increasing the reactivity of the precursors using an attrition ball milling apparatus, resulting in optimal final microstructure and electromechanical properties. A further implementation involved the introduction of the freeze-drying step, which enabled the development of a scalable water-based solid-state route. In parallel, a non-toxic sol-gel route was successfully optimised. The toxicity of the system was also analysed. The impact of poling field parameters on crystalline phase evolution was also studied using an innovative device usable with the laboratory diffractometer. In summary, this PhD Thesis work proposes scalable, non-toxic and environmentally sustainable processing routes to obtain high-sensitivity BCZT ceramics for novel biomedical applications.