Development of novel lead-free piezoceramic shear and torsion transducers

The present project will address the development of lead-free piezoceramic d15 shear and torsion transducers with enhanced response. The significant rise in scientific research on piezoelectric materials is related to their extensive range of applications in structural health monitoring, damping of vibrations, sound reduction, shape control, energy harvesting, bio-medical industries and so on. These applications utilize the excellent actuation and sensing capabilities of piezoelectrics. However, piezoelectric devices containing lead-based materials are required to eliminate the lead due to its toxic nature to human health. There are increasing level of worldwide restrictions on the use of lead-based materials. Thus, recently, lead-free piezoceramic materials have been demanded to meet this need and improve the environmental protection. Lead-free NBT-BT (Na0.5Bi0.5TiO3BaTiO3) piezoceramic system has emerged as a potential candidate to replace the lead-based piezoelectrics due to its high E- field induced strain, high piezoelectric response and easy synthesizability. For this purpose, lead-free NBT-BT piezoceramic system, is proposed to be utilized in d15 shear-mode and meet the needs of high performance shear and torsion transducers. A promising approach in the enhancement of piezoelectric shear response of lead-free NBT-BT is through texturing in (111) grain orientation. In grain-oriented ceramics, the chaotic ordering of domains is transformed into a more ordered structure. The orientation of the polar axis in each grain is in the same direction and quantified through the calculation based Lotgering factor. In the present research, (111)-oriented lead-free NBT-BT piezoceramics will be developed and characterized for the d15-shear-response for the first time. This research will provide the estimation of the magnitude of piezoelectric d15 shear constant of lead-free piezoceramics with different magnitude of Lotgering factor, process for synthesizing lead-free NBT- BT (111)-textured ceramics, and performance of lead-free piezoceramic d15 shear and torsion transducers. Experimental benchmarks will be manufactured from NBT-BT systems with maximized d15 shear responses for selected shear and torsion transduction applications. The sensing and actuation capabilities of the benchmarks will be experimentally monitored under dynamic conditions. The benchmarks will be further modelled and verified by the Finite Element (FE) code ABAQUS. The analytical modeling of the lead-free NBT-BT piezoceramic d15 shear and torsion transducers will be performed by using the transfer matrix and exact 3D Saint-Venant type formulations. Another key aspect of the present project is to direct the existing research on lead-based piezoelectric structures in Austria to the lead-free piezoceramics. The lead-free piezoceramics are not currently in mass production in the world and studies of lead-free piezoceramic transducers with respect to the synthesis processes will develop the required knowledge base in this area. For this reason, in the return phase of the project, the know-how of novel production methods of lead-free d15 piezoceramics with high piezoelectric response will be transferred to Austria.

The present project addresses the development of lead-free piezoceramic d15 shear and torsion transducers with enhanced response. The significant rise in scientific research on piezoelectric materials is related to their extensive range of applications in structural health monitoring, damping of vibrations, sound reduction, shape control, energy harvesting, bio-medical industries and so on. These applications utilize the excellent actuation and sensing capabilities of piezoelectrics. However, piezoelectric devices containing lead-based materials are required to eliminate the lead due to its toxic nature to human health. There are increasing level of worldwide restrictions on the use of lead-based materials. Thus, recently, lead-free piezoceramic materials have been demanded to meet this need and improve the environmental protection. Lead-free NBT-BT (Na0.5Bi0.5TiO3BaTiO3) piezoceramic system has emerged as a potential candidate to replace the lead-based piezoelectrics due to its high E-field induced strain, high piezoelectric response and easy synthesizability. For this purpose, lead-free NBT-BT piezoceramic system, is proposed to be utilized in d15 shear-mode and meet the needs of high performance shear and torsion transducers. A promising approach in the enhancement of piezoelectric shear response of lead- free NBT-BT is through texturing in (111) grain orientation. In grain-oriented ceramics, the chaotic ordering of domains is transformed into a more ordered structure. The orientation of the polar axis in each grain is in the same direction and quantified through the calculation based Lotgering factor. In the present research, (111)-oriented lead-free NBT-BT piezoceramics is developed and characterized for the d15-shear-response for the first time. This research provides the estimation of the magnitude of piezoelectric d15 shear constant of lead-free piezoceramics with different magnitude of Lotgering factor, process for synthesizing lead-free NBT-BT (111)-textured ceramics, and performance of lead-free piezoceramic d15 shear transducers. This study demonstrates a lead-free piezoceramic exhibiting giant piezoelectric shear stress coefficient (e15) and piezoelectric transverse shear actuation force comparable to that of lead-based shear-mode piezoceramics. The Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C/m2. The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d15 mode piezoceramic shear patches, provided a rate of twist of 0.08 mm/m/V under quasi-static 150V drive. The high value of piezoelectric shear d15 coefficients in NBT-BT-Mn sample further demonstrated its potential in practical applications. These results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts.Keywords: lead-free, piezoceramic, d15 shear-mode, torsion, transducer, experiment