Performance Enhancement and Ultrasonic Transducer Application of Bi/Li Codoped Ba0.95Ca0.05Ti0.95Zr0.05O3 Lead-Free Ceramics.

In this study, a series of (1 - x)(Ba0.95Ca0.05)(Ti0.95Zr0.05)O3-x(Bi0.5Li0.5TiO3) ceramics (x = 0-0.007) codoped with Bi and Li elements were prepared by solid-phase sintering. Bi/Li codoping induces lattice distortion, reduces domain size, and increases tetragonal phase content, thereby enhancing the comprehensive performance of the BCTZ ceramics. The 0.994BCTZ-0.006BLT ceramic exhibits optimal performance: piezoelectric coefficient d33 = 270 pC/N, remnant polarization Pr = 7.3 μC/cm2, Curie temperature Tc = 112 °C, electromechanical coupling factors kp = 0.19 and kt = 0.45, sound velocity c = 5200 m/s, and dielectric loss tan δ = 0.0222. A 10 MHz planar ultrasonic transducer fabricated from this ceramic shows a pulse-echo peak-to-peak voltage Vpp of 206.74 mV, center frequency fc of 11.01 MHz, -6 dB bandwidth of 57.9%, and lateral resolution Rlateral of 0.95 mm. After acoustic focusing, the transducer's performance is further improved: Vpp = 233.53 mV, fc = 10.25 MHz, -6 dB bandwidth = 72.48%, and the lateral resolution Rlateral = 0.64 mm. Imaging tests on coins and porcine eyeballs demonstrate clear surface details/patterns of coins and excellent visualization of the conjunctiva, cornea, lens, and iris. This demonstrates its potential in the nondestructive testing and biological imaging fields.