Ultrasound diagnostic technology demonstrates unique clinical value in cardiovascular monitoring, precise ophthalmic diagnosis, and interventional therapy, offering advantages of high efficiency, safety, non-invasiveness, and significant cost-effectiveness. As the core component of ultrasound imaging systems, transducers’ performance directly determines the image resolution. Piezoelectric materials, essential for the acoustic-to-electric energy conversion, exhibit piezoelectric and electromechanical properties that decisively influence transducer sensitivity and bandwidth. While commercial Pb(Zr,Ti)O₃ (PZT) ceramics offer excellent performance, the toxicity of the lead element throughout material preparation, service life, and disposal poses significant risks to human health and ecosystems.
[001]_C-textured lead-free (Ba,Ca)(Zr,Ti)O₃ (BCZT) ceramics were fabricated via the Template Grain Growth (TGG) method. The materials demonstrate high piezoelectricity, elevated sound velocity, and low dielectric constant, making them highly suitable for developing high-sensitivity and large-bandwidth ultrasonic transducers. However, critical limitations also persist: (1) the absence of full-matrix electromechanical properties such as dielectric constant ε_ij, piezoelectric coefficient d_ij, and elastic constant s_ij essential for device design, and (2) the restriction of electromechanical coupling coefficient k calculations to extreme aspect ratios. The inability to accurately model k evolution at finite aspect ratios severely constrains practical applications.
To overcome such challenges, highly [00l]_C-oriented textured BCZT ceramics (texture degree f_00l ~ 98%) were synthesized via TGG. The complete full-matrix electromechanical property dataset was established for the first time by integrating resonance-antiresonance spectroscopy with pulse-echo ultrasonic measurements. The textured BCZT ceramics exhibit strong anisotropic Poisson’s ratios. Their piezoelectric coefficient d₃₃ (605 pC/N) and electromechanical coupling coefficient k₃₃ (0.73) is comparable to that of PZT-5H ceramics, while the piezoelectric voltage constant g₃₃ (23.6× 10^-3 (V/m/)Pa) is 20 % higher than that of PZT-5H.
Using the piezoelectric constitutive equations, we developed a theoretical model to predict k at arbitrary aspect ratios. Based on this developed model, the 1-3 BCZT composite transducer with high sensitivity and wide frequency band was designed and fabricated, exhibiting a center frequency of ~ 3.0 MHz. The BCZT transducer achieves an insertion loss of -33.0 dB. The -6 dB bandwidth is as high as 107.1%, which is superior to the ultrasonic transducer made of PZT-5H composite reported in literatures. This work not only provides complete electromechanical parameters for lead-free piezoelectric device applications but also lays a theoretical and technical foundation for the development of high-performance, eco-friendly ultrasonic diagnostic equipments.