• • Perovskite, wurtzite, and fluorite structures each exhibit distinct piezoelectric coefficients (e.g., PZT ceramics achieve d33 > 500 pC/N, while AlN thin films show d33 ~5 pC/N), dictating their suitability for high-sensitivity sensors versus high-frequency MEMS applications.
• • Defect engineering in Pb-based ceramics, as reported in reference [282], integrates phase boundary and defect engineering to achieve extremely high piezoelectric properties, with d33 values exceeding 800 pC/N, enabling precision actuators with sub-micron displacement control.
• • Heterostructure film fabrication, exemplified by KNN-based ferroelectric heterojunctions (reference [273]), enables frequency-adjustable behavior, achieving tunable resonance frequencies from 1 kHz to 10 MHz for biomedical ultrasound applications.
• • Composite film design, such as 3D PVDF piezoelectric nanoyarn fabric (reference [274]), demonstrates ultrahigh strength and sweat permeability, with strain sensitivity reaching 0.1% and output voltage of 2 V under mechanical deformation, suitable for wearable health monitors.