A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Electroactive phases of poly(vinylidene fluoride) : determination, processing and applications

Multiferroic magnetoelectric composite systems such as ferromagnetic-ferroelectric heterostructures have recently attracted an ever-increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Recent Progress in Multiferroic Magnetoelectric Composites: from Bulk to Thin Films

Investigations in the development of lead-free piezoelectric ceramics have recently claimed comparable properties to the lead-based ferroelectric perovskites, represented by Pb(Zr,Ti)O3, or PZT In this work, the scientific and technical impact of these materials is contrasted with the various families of “soft” and “hard” PZTs On the scientific front, the intrinsic nature of the dielectric and piezoelectric properties are presented in relation to their respective Curie temperatures (T
 C) and the existence of a morphotropic phase boundary (MPB) Analogous to PZT, enhanced properties are noted for MPB compositions in the (Na,Bi)TiO3-BaTiO3 and ternary system with (K,Bi)TiO3, but offer properties significantly lower The consequences of a ferroelectric to antiferroelectric transition well below T
 C further limits their usefulness Though comparable with respect to T
 C, the high levels of piezoelectricity reported in the (K,Na)NbO3 family are the result of enhanced polarizability associated with the orthorhombic-tetragonal polymorphic phase transition being compositionally shifted downward As expected, the properties are strongly temperature dependent, while degradation occurs through the thermal cycling between the two distinct ferroelectric domain states Extrinsic contributions arising from domains and domain wall mobility were determined using high field strain and polarization measurements The concept of “soft” and “hard” lead-free piezoelectrics were discussed in relation to donor and acceptor modified PZTs, respectively Technologically, the lead-free materials are discussed in relation to general applications, including sensors, actuators and ultrasound transducers

Lead-free piezoelectric ceramics: Alternatives for PZT?

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

Effects of grain size on the dielectric properties and tunabilities of sol–gel derived Ba(Zr0.2Ti0.8)O3 ceramics

Lead magnesium niobate-lead titanate 0.67Pb (Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.33PbTiO/sub 3/ (PMN-0.33PT, abbreviated as PMN-PT) single crystals were used to fabricate PMN-PT/epoxy 1-3 composites with different volume fractions of PMN-PT ranging from 0.4 to 0.8. The electromechanical properties of the 1-3 composites were determined by the resonance technique. Theoretical modeling of the 1-3 composites matched quite well with the measured material properties. It was demonstrated that the thickness electromechanical coupling coefficients of the composites could reach as high as 0.8. A 2.4 MHz plane ultrasonic transducer was fabricated using a PMN-PT/epoxy 1-3 composite with 0.37 volume fraction of PMN-PT. It shows a -6 dB bandwidth of /spl sim/61% and an insertion loss of -14 dB.

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Single crystal PMN-0.33PT/epoxy 1-3 composites for ultrasonic transducer applications

Piezoelectric and ferroelectric properties of KxNa1−xNbO3 lead-free ceramics with MnO2 and CuO doping

A microfluidic approach for fabrication of Janus hydrogel particles with magnetic anisotropy is demonstrated. Using this technique, cells and magnetic beads (MBs) can be separately embedded in one hydrogel particle to maintain optical performance, and reduce the contact between cells and magnetic beads (nano- or submicron-particles). Alginate cell capsules prepared by this method can be easily controlled and manipulated by external magnetic fields and require no specific surface modification. Bio-degradability and super-paramagnetic properties of these hydrogel particles were also demonstrated experimentally.

Generation of Janus alginate hydrogel particles with magnetic anisotropy for cell encapsulation

Multiferroic nanocomposite films composed of P(VDF-TrFE) copolymer and CoFe2O4 (CFO) nanoparticles have been prepared by a modified polymeric processing Structural characterizations reveal that CFO nanoparticles with 80–100 nm diameters are well distributed in the P(VDF-TrFE) matrix The crystalline and microstructure of P(VDF-TrFE) are strongly dependent on the volume fraction of CFO nanoparticles, which are further analyzed by Raman spectra Consequently, the ferroelectric and magnetoelectric responses are strongly influenced by the concentration of CFO nanoparticles A significant magnetoelectric coupling effect of around 40 mV/cm Oe is obtained from the nanocomposites A relatively simple model has been adopted to calculate the magnetoelectric coefficient, which is also in agreement with the experimental results

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H.L.W. Chan

Papers

Effects of grain size on the dielectric properties and tunabilities of sol–gel derived Ba(Zr0.2Ti0.8)O3 ceramics

Single crystal PMN-0.33PT/epoxy 1-3 composites for ultrasonic transducer applications

Piezoelectric and ferroelectric properties of KxNa1−xNbO3 lead-free ceramics with MnO2 and CuO doping

Generation of Janus alginate hydrogel particles with magnetic anisotropy for cell encapsulation

The effect of magnetic nanoparticles on the morphology, ferroelectric, and magnetoelectric behaviors of CFO/P(VDF-TrFE) 0–3 nanocomposites