Exploring lead-free materials for screen-printed piezoelectric wearable devices

The rapid advancements in wearable technology demand innovative materials that are flexible, lightweight, and environmentally sustainable. Here, we report the formulation, characterization, and application of screen-printed piezoelectric inks consisting of barium titanate (BT), barium calcium zirconate titanate (BCZT), and potassium sodium niobate (KNN) for flexible piezoelectric sensors. X-ray diffraction and scanning electron microscopy reveal high crystallinity and distinct morphologies. Rheological experiments show excellent printability; however, the BCZT-based ink reveals shear thickening behavior and a lower recovery rate of 63.5% during printing. Thermal gravimetric and Fourier transform infrared spectral analyses provide insights into the inks' thermal and chemical stability. The screen-printed composites exhibit excellent adhesion to the substrates and consistent dielectric properties across a wide frequency range. A detailed investigation of the piezoelectric charge coefficient d33 under varying poling conditions is carried out using corona discharge poling. The study provides a comprehensive understanding of the role of ceramic fillers in influencing the rheological, thermal, and piezoelectric properties of screen-printed piezoelectric inks, guiding the development of customizable flexible sensors.