Lead-Free Piezoceramic Materials for SONAR Transducer Applications

For this project, bismuth ferrite-barium titanate (BF-BT) compounds are doped with Mn and Sm and are prepared and investigated for their piezoelectric properties. A variety of processing variables are used to investigate their effect on the piezoelectricity and structure of the different compositions, which will help optimize the materials’ piezoelectricity. The dielectric and piezoelectric properties of the materials are measured using piezoelectric resonance methods such as Berlincourt measurements, ferroelectric hysteresis and PRAP. A series of impedance measurements are also done to compare the conductivity between different compositions.
For Sm-doped BF-BT, the formula used was 0.67Bi1.03FeO3-0.33[Ba1-xSmxTiO3], where x=0.00-0.03. The best results achieved were a d33 of 85 pC/N and Tc of 433oC, at x = 0.01.
For Mn-doping, the formula used was 0.67(Bi1-x¬Mnx)FeO3-0.33BaTiO3, where x=0.01-0.02. The process of air-quenching (fast cooling from 1000oC to room temperature) has reduced defects in its crystal structure and has improved its piezoelectric performance in comparison to slow-cooling. The best results achieved were for air-quenched Mn-doped BF-BT with a d33 of 176 pC/N and Tc of 450oC, also at x=0.01. This is an improvement over slow-cooled BF-BT-Mn which recorded a d33 of 91pC/N with the same variables.
Co-doping BF-BT with both Mn and Sm achieved a maximum d33 of 161 pC/N and a Tc of 495oC after air-quenching.
Impedance measurements have shown that the activation energy Ea decreases with air and water-quenched samples, and that higher conductivities correlate with lower d33 values, indicating electron conductivity to the limiting factor to the d33.