Lead-free piezoelectric materials and composites for high frequency medical ultrasound transducer applications

Lead-free ceramics based on the (1-x)Ba(Zr_0.2Ti_0.8)O_3-x(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) system have been reported to exhibit piezoelectric properties comparable to lead zirconate titanate ceramics, and are thus being considered as replacement materials for some applications. In this work, the possibility of fabricating BZT-BCT based 1-3 piezocomposites for high frequency ultrasound imaging has been explored. An investigation of the interdependence of synthesis, processing and sintering conditions on the physical, structural, microstructural and functional properties of piezoelectric compositions in the BZT-BCT system has been carried out. Ceramic powders with a composition of 0.5BZT-0.5BCT and a particle size of 1 μm were chosen for the fabrication of the ceramic segments which were subsequently sintered at 1425°C. A novel randomised pattern that has recently demonstrated its advantages in suppressing undesirable spurious resonances was adopted for the lead-free composites and a micro-moulding technique based on gel casting ceramic processing has been used for the fabrication of the composites. A 0.5BZT-0.5BCT based randomised composite operating at ~30 MHz with an electromechanical coupling factor of 0.63 has been achieved.