| In this research, an attempt has been made to develop and characterize lead-free ceramics, transducers, and thin films based on Bi0.5Na 0.5TiO3 (BNT) compositions.;BNT-based ceramics with different compositions were prepared by mixed oxide route. The electromechanical and acoustic properties of the ceramics were studied. 0.88BNT-0.08BKT-0.04BT (BNKTBT88) and 0.076BNT-0.20BKT-0.04BLT (BNKLT76) ceramics showed relatively high values of piezoelectric coefficient (d33~170-175 pC.N-1), dielectric constant (850-950), and planar coupling coefficient (kp~0.32-0.37). On the other hand, BNKLT88 ceramics with a rhombohedral structure exhibited high mechanical quality factor (Qm~420). Acceptor dopants such as Mn and Fe were doped in BNKLT88 ceramics. By optimizing the powder processing and sintering temperature, Qm values as high as 900-975 were obtained in 1.5 mol.% Fe or Mn-doped ceramics sintered at 1100 °C. This composition showed the maximum vibration velocity (0.6 m.s-1), minimum heat generation, minimum input power, and the best efficiency among the studied compositions.;High frequency ultrasonic transducers for medical imaging were designed and fabricated based on the BNKLT88 ceramics. The focused transducer with a center frequency of 23 MHz, exhibited a -6dB bandwidth and insertion loss of 55% and -32.1 dB, respectively. B-mode images of a wire phantom (30 microm in diameter) were produced by the transducer.;BNT-based thin films with four different compositions in BNT-BKT-BT as well as BNT-BKT-BLT systems were deposited on (001)-oriented SrRuO3/SrTiO 3 substrates by pulsed laser deposition technique. The effects of deposition parameters on the microstructure, chemical composition, and electrical properties of thin films were evaluated. Under optimized condition, BNKTBT88 thin films exhibited a remnant polarization of about 30 muC.cm-2 and coercive field of 85 kV.cm-1. The dielectric constant and loss tangent at 1 kHz were measured to be 645 and 0.052, respectively. The leakage current of epitaxial BNKTBT88 thin films measured at different temperatures was matched with the Lampert's triangle bounded by three straight lines of different slopes. It was shown Mn-doping suppressed the leakage current by more than two orders of magnitude. The remnant polarization and dielectric constant (at 10 kHz) of Mn-doped BNKLT76 film deposited at 400 mtorr were measured to be 23 microC.cm-2 and 660, respectively. |
