Potassium sodium niobate based lead-free ceramic for high-frequency ultrasound transducer applications

The BiAlO3 (BA) and (Bi0.5Na0.5)ZrO3 (BNZ) are selected to form a solid solution with (K0.48Na0.52)NbO3 via traditional solid state technique to optimize the electrical performance and temperature stability of KNN-based lead-free ceramics, simultaneously. Here we show that doped BA has a great influence on phase structure, morphologies, and electrical properties. The XRD patterns and dielectric constant versus temperature curves reveal that an increase in the BA content results in a transform of phase structures from a coexistence state of rhombohedral, orthorhombic and tetragonal phases to pseudocubic phase. Owing to the construction of R-O-T phase boundary, optimized performances (TC ∼ 336 °C, d33 ∼ 306 pC/N, kp = 0.48) are obtained in 0.962(K0.48Na0.52)NbO3-0.003BiAlO3-0.035(Bi0.5Na0.5)ZrO3 (KNN-3) ceramics. Based on the sintered KNN-3 ceramic samples, high-frequency ultrasound imaging transducers are designed and fabricated, which exhibits a high center frequency of 24.5 MHz, a broad −6 dB bandwidth of 97% and a high-sensitivity. Finally, the imaging characteristic of the lead-free transducers is demonstrated via ex vivo imaging of biological tissue structure. As environment friendly materials, the excellent electrical and acoustic performance of developed KNN-based ceramics has great potential for practical applications.