Electrical properties and temperature behavior of ZnO-doped PZT-PMnN modified piezoelectric ceramics and their applications on therapeutic transducers

Pb_0.98Ca_0.01Sr_0.01[(Mn _1/3Nb_2/3)_0.054Cu_0.006-(Zr _0.52Ti_0.48)_0.94]O₃ (PMNCZT) + x wt.% ZnO (PMNCZT-Z10x) ceramics were prepared and sintered at a low temperature 980 °C, using the modified mixed-oxide method. The phase structure and microstructure evolutions were examined by XRD and SEM analyses. Effects of ZnO additives on the dielectric relaxation, piezoelectric, temperature stability, and ferroelectric properties were systematically investigated. The results showed that the ZnO doping increased the tetragonality ratio, tetragonal phase fraction, and long-range order degree of crystal structure. In addition, the electromechanical coupling factors, and the temperature stability of resonance frequency and resonant resistance were improved with increasing the ZnO amounts until x = 1. Beside these properties, the decrease of Q_m was related to decreasing in normalized change value of space charge. This developed compositions had k_p and k_t of 0.56 and 0.55, Q_m of 1280, d₃₃ of 285 pC/N, 33T/⁰ of 980, tan δ of 0.0023, coercive field (E_c) of 11 kV/cm, and remnant polarization (P_r) of 28 μC/cm². Their corresponding transmission coefficient of intensity exhibited from value of 60.12% (x = 0) to value of 68.56% (x = 2) by the acoustic model calculation. To evaluate the dynamic performance of developed piezoceramics, a 3 MHz therapeutic transducer was fabricated using the trade-off ceramics with x = 0.5. Its properties exhibited that the average effective coupling factors keff2 of 5.6%, electro-acoustic efficiencies of 34.1%, and dynamic acoustic power 0.75 W were better than those of a commercial transducer.