Multidimensional synergy-induced high piezoelectricity and reliability KNN piezoceramics for high-frequency ultrasonic transducers

High-frequency ultrasonic transducers have been implemented as a powerful tool for modern medical diagnosis and therapy. Most current transducers use piezoelectric ceramics for electromechanical couplings, which will undergo periodic electro-acoustic transitions at high frequencies (≥20 MHz), thereby requiring high reliability. This work presents a structural engineering strategy to improve the piezoelectricity and reliability of potassium sodium niobate (KNN)-based ceramics with potential high-frequency ultrasonic imaging transducers. The KNN-based ceramics exhibit fatigue-free behavior with enhanced piezoelectricity ( d 33 ∼550 ± 20 pC N −1 ), and the mechanisms are discussed in view of multi-dimensions from macroscopy to microscopy. Considering the synergistic effect of multi-phase coexistence, well-kept microstructure, and flexible domain rotation, property-worsening cracks during fatigue are restrained; furthermore, the aggregation of space charges is hindered, thereby reducing the pinned domain and improving the fatigue resistance. Based on the high-performance piezoceramics, the fabricated ultrasonic transducer has high reliability with a steady sensitivity and an unchanged broad bandwidth (∼76%) from room temperature to 80°C. In addition, images of a tilapia eyeball are scanned to confirm the imaging capability of transducers. We expect that the novel approach to achieving high performance through the structural strategy promotes KNN-based ultrasonic devices for biomedical imaging.