Abstract
Environmental and safety concerns with respect to the utilization, recycling, and disposal of Pb-based ferroelectric materials and transducers have led to a new surge in developing lead-free ferroelectric materials. (K, Na)NbO3, (Bi1/2Na1/2)TiO3 and BiFeO3 based compositions are among the most promising candidates for such lead-free ferroelectric materials.
The KNN based system is very sensitive to processing conditions such as purity of oxides and the humidity of the ambient in which processing is accomplished.  Despite such sensitivity, Ceramics with different compositions and additives with high electromechanical properties have been reported.
In the BNT based solid solution, the highest piezoelectric properties are at the MPB between Rhombohedral and tetragonal phases. The tetragonal side of the MPB with high Td is suitable for actuators and composition in the rhombohedral side with high mechanical quality factor is suitable for high power transducer applications. We have been studying 0.88Bi1/2Na1/2TiO3 – 0.08Bi1/2K1/2TiO3 – 0.04BaTiO3 /0.04Bi Li TiO3 (BNKBT88 and BNKLT88) compositions and successfully developed and demonstrated: i) Low temperature sintering using additives, ii) Co-firing ceramics with copper electrodes in controlled oxygen atmosphere, iii) Either Mn doping of BNKLT88 OR developing non-stoichiometry compositions to achieve Pb-free piezoelectric ceramics with soft or hard properties for actuator and high power applications, and (v) designed, fabricated and evaluated single element Pb-Free ultrasound transducer with high and low center frequency for medical imaging and HIFU applications.
In BiFeO3 (BFO) based system, We’ve used the electrospinning technique to obtain 20 to 100 nm ultra-thin nanofibers of bismuth ferrite by precisely varying the concentration of the precursor solution. We obtained (for the first time to our knowledge), a mobility of 0.2 cm2/V.s for top gated single-fiber devices and 0.25 cm2/V.s for top gated multi-fiber devices. From optoelectrical measurements, it was  observed that nanofibers of thin diameter (~20 nm) exhibit almost 100 times higher photoresponse compared to nanofibers of thicker diameter.