Performance Enhancement and Ultrasonic Transducer Application of Bi/Li Codoped Ba 0.95 Ca 0.05 Ti 0.95 Zr 0.05 O 3 Lead-Free Ceramics

In this study, a series of (1 – x )(Ba 0.95 Ca 0.05 )(Ti 0.95 Zr 0.05 )O 3 - x (Bi 0.5 Li 0.5 TiO 3 ) 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 d 33 = 270 pC/N, remnant polarization P r = 7.3 μC/cm 2, Curie temperature T c = 112 °C, electromechanical coupling factors k p = 0.19 and k t = 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 V pp of 206.74 mV, center frequency f c of 11.01 MHz, −6 dB bandwidth of 57.9%, and lateral resolution R lateral of 0.95 mm. After acoustic focusing, the transducer’s performance is further improved: V pp = 233.53 mV, f c = 10.25 MHz, −6 dB bandwidth = 72.48%, and the lateral resolution R lateral = 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.