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Electromechanical properties and high power characteristics of Pb-free hard piezoelectric ceramics in the (BiNa 0.88 K 0.08 Li 0.04 ) 0.5 (Ti 1 -x Mn x )O 3 (x = 0, 0.014, 0.015, and 0.016) system were studied. Mn doping resulted in a considerable enhancement of mechanical quality factor Q m and vibration velocity. The lowest mechanical and dielectric losses were achieved in 1.5 mol% Mn-doped ceramics with a planar Q m of about 970 and tand of 0.89%. The heat dissipation and resonance frequency shift under high drive condition were remarkably suppressed upon Mn doping. The maximum vibration velocity was increased from 0.28 m/s in undoped ceramic to 0.6 m/s in 1.5 mol% Mn-doped composition. The results of this study revealed that Mn-doped BNT-based piezoelectrics exhibited a superior high power performance compared to their lead-based counterparts such as PZT4 and PZT8 ceramics.

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We have studied the processing and electromechanical properties of Mn and Fe‐doped 0.88[Bi0.5Na0.5TiO3]–0.08[Bi0.5K0.5TiO3]–0.04[Bi0.5Li0.5TiO3] piezoelectric ceramics prepared by the mixed oxide route. Different amounts of Mn (0.01, 0.014, 0.015, 0.016, 0.017, 0.02, 0.022) or Fe (0.0125, 0.015, 0.0175) were doped to this lead‐free piezoelectric composition. Ceramics were sintered at different temperatures (1075°C–1150°C) to achieve the highest density and mechanical quality factor. Mn or Fe doping resulted in a considerable enhancement of Qm in both planar and thickness resonance modes. In 1.5 mol% Mn‐doped ceramics sintered at 1100°C, a planar Qm of about 970 and tanδ of 0.88% were obtained. In Fe‐doped ceramics, a planar Qm as high as 900 was achieved. Acceptor dopants also resulted in decreasing the coupling coefficients, the piezoelectric charge coefficient, and the dielectric constant.

Piezoelectric materials have been vastly used in ultrasonic transducers for medical imaging. In this paper, firstly, the most promising lead-free compositions with perovskite structure for medical imaging applications have been reviewed. The electromechanical properties of various lead-free ceramics, composites, and single crystals based on barium titanate, bismuth sodium titanate, potassium sodium niobate, and lithium niobate are presented. Then, fundamental principles and design considerations of ultrasonic transducers are briefly described. Finally, recent developments in lead-free ultrasonic probes are discussed and their acoustic performance is compared to lead-based transducers. Focused transducers with different beam focusing methods such as lens focusing and mechanical shaping are explained. Additionally, acoustic characteristics of lead-free probes including the pulse-echo results as well as their imaging capabilities for various applications such as phantom imaging, in vitro intravascular ultrasound imaging of swine aorta, and in vivo or ex vivo imaging of human eyes and skin are reviewed.