| Lead-free piezoelectric ceramics, 0.90Bi0.5Na 0.5TiO3-0.05Bi0.5K0.5TiO3-0.05BaTiO 3 (BNKBT-5), have been fabricated by a solid-state reaction method. The dielectric, piezoelectric and ferroelectric properties of the ceramics have been measured and the microstructures studied by X-ray diffraction and SEM. In the ferroelectric hysteresis loop measurements, Pr ∼ 28.5 muC/cm2 and Ec ∼3.5 MV/m have been observed. The electromechanical coupling coefficients kp and kt are 0.31 and 0.46, respectively. Those properties are comparable to that of lead-based ceramics such as PZT.; Three different compounds, including CeO2, Ca2Fe 2O5 and (Bi0.5Li0.5)TiO3, have been used as additives/dopants to improve the properties of BNKBT-5. All the samples with different compositions have been characterized. The measured properties are compared with that of BNKBT-5. It has been found that the BNKBT-5 doped with 1.5 mol% of (Bi0.5Li0.5)TiO3, namely BNKLBT-1.5, has the best performance. It can enhance kp, kt, Qm, Pr, and can reduce tandelta but do not lower the depolarization temperature.; Two different types of devices have been fabricated using BNKBT-5 and BNKLBT-1.5 ceramic rings. The first device is compressive-type accelerometers. A PZT accelerometer with similar structure has also been fabricated for comparison. The accelerometers are calibrated using a back-to-back calibration method against a standard reference accelerometer. Within the +/-2.5% tolerance, the mean sensitivity of PZT, BNKBT and BNKLBT accelerometer is 4.34 pC/ms -2 (50 Hz to 8.24 kHz), 2.24 pC/ms-2 (50 Hz to 10.1 kHz) and 2.97 pC/ms-2 (50 Hz to 12.45 kHz), respectively. The BNKLBT-1.5 accelerometer has a reasonably high sensitivity and the broadest sensing frequency range which would be the most preferable choice for structural health monitoring applications.; The second device is ultrasonic wirebonding transducers for microelectronic packaging. It has been found that if titanium is used as the metal parts in the transducer, the BNKLBT-1.5 transducer has similar axial displacement (∼1.6 mum) to that of PZT/stainless steel (state-of-the-art transducer) transducer presumably because the lead-free ceramic has an acoustic impedance close to that of titanium metal. The lateral displacement of the BNKLBT-1.5 is much smaller than that of PZT transducer thus can improve the bonding quality. It shows that lead-free ceramics has the potential to replace PZT in certain transducer designs. |
