High-performance potassium sodium niobate piezoceramics for ultrasonic transducer

Ultrasonic transducers can be used as medical diagnostic imaging and nondestructive testing. This work presents phase structure engineered high-performance potassium sodium niobate [(K,Na)NbO₃, KNN]-based ceramics and its potential application on ultrasonic transducer. A connection among structural engineering, electrical properties, and prototype device designing was established in lead-free KNN-based ceramics. Structural elucidation through atomic resolution polarization mapping by Z-contrast imaging indicates that the nanoscale balanced multiple phase coexistence (R-O-T) is the origin of both enhanced piezoelectricity and improved temperature stability: high d₃₃ of 500 pC/N and improved in-situ temperature stability of d₃₃ (less than 24% variation for d₃₃ from 25 to 100 °C), together with the improvement of electromechanical coupling coefficient (k_p~0.5 and k_t~0.55). Based on the high-performance ceramics, a 1–3 composite ultrasonic transducer with a center frequency of 5 MHz is produced, and a bandwidth of 81% at −6 dB is substantially higher than that of PZT-based transducers at the same center frequency. We believe the novel way to improve electrical properties through structural engineering could open a new road to promote the practical application of KNN-based ceramics.