Development of bimorph vibrator using lead free BNT piezoelectric film deposited by hydrothermal method
PZT piezoelectric film synthesized hydrothermally has been studied actively in our laboratory. However, it is apprehended recently that PZT affects health and the environment, because PZT is chemical compound containing lead. Therefore, we tried to synthesize lead free BNT piezoelectric film on titanium substrate hydrothermally. The synthesized BNT films on titanium substrates were evaluated with SEM image, XRD pattern and EDS. We fabricated bimorph vibrators with synthesized lead free BNT film and evaluated their performances.
Synthesis and Characterization of Piezoelectric (Bi1/2Na1/2)TiO3 Films by a Hydrothermal Method
Thin films of lead-free piezoelectric ceramics (Bi1/2Na1/2)TiO3 (abbreviated as BNT) were prepared on pure titanium substrates by a hydrothermal method. The properties of BNT films synthesized from the reaction solution with various contents of bismuth and titanium were investigated using SEM, EDX, XRD and other instruments. Moreover, the effects of the concentrations of starting materials on permittivity and piezoelectric effect of deposited BNT films were discussed. The results showed that an impurity of Bi2O3 crystal was produced on the surfaces of all deposited films. With assumption of deposited films as an system of (1-x) (Bi1/2Na1/2)TiO3-xBi2O3, the BNT content was calculated from the Bi/Ti ratio of the EDX results. The optimized synthesis condition was determined on the evaluation target of the calculated BNT content. In addition, the unimorph cantilever type actuators were fabricated by BNT deposited samples, and their piezoelectric responses were measured at their resonance frequencies under AC field. It was noted that the piezoelectric effect of the deposited BNT film was greatly dependent on its crystallization level.
Characterization of Bi0.5Na0.5TiO3‐PbTiO3M Dielectric Materials
Bi 0.5 Na 0.5 TiO 3 (BNT) modified with Pb showed an increased and broadened dielectric constant and limited grain growth. Pb also lowered the first transition temperature. The phases of BNT were confirmed to be ferroelectric at room temperature which transformed to antiferroelectric above 220°C. When BNT was doped with 10% Pb, the first transition decreased to 140°C and abruptly disappeared in the composition with 17% Pb. The crystal structure of 17%-Pb-doped BNT at room temperature is tetragonal, which differs from the rhombohedral structure at lower Pb contents. Thus, the phase boundary between rhombohedral and tetragonal ferroelectric phase was determined to be between 15% to 17% Pb in this study.