Transmission Electron Microscopy Studies of Phase Transformations in Lead-free Morphotropic Phase Boundary Ferroelectrics

Piezoelectric materials that convert mechanical to electrical energy (and vice versa) are used extensively in medical imaging transducers, actuators, and other electronic devices. The most widely used piezoelectric ceramics are lead oxide based ferroelectrics, especially Pb(Zr,Ti)O3(PZT). PZT ceramics are high-performance piezoelectric materials and exhibit high piezoelectric properties close to a morphotropic phase boundary (MPB). However, PZT-based ceramics contain a large amount of lead, which has recently been expelled from many commercial applications due to its toxicity. Using lead-free materials is desired for environmental protection. High piezoelectric properties have recently been discovered in modified (Na1/2Bi1/2)TiO3(NBT) and (Na1/2K1/2)NbO3(NKN) ceramics of compositions close to MPBs. This is an important and timely discovery, about which much research and development remains to be done. The objectives of this project are (i) to investigate the mechanism by which high piezoelectricity is achieved in lead-free materials, and (ii) to identify similarities and differences in microstructure between MPBs in lead-free and lead-based systems. Developing lead-free ferroelectric ceramics with high piezoelectric properties is an important area of research not only scientifically, but also technically, as these lead-free systems will eventually be the cornerstone of a billion dollar world-wide industry.