Perspective on the Development of Lead‐free Piezoceramics

Abstract

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.

Hallmarks of mechanochemistry: from nanoparticles to technology

“…PZT. 271,272 So far, the (K,Na)NbO 3 (KNN) solid solution has been one of the most studied among the alternatives. 273 The research on KNN was reinforced in 2004 by the paper of Saito et al, 274 who showed that piezoelectric properties comparable to PZT could be achieved by modifying KNN with Li, Ta and Sb, or by grain orientation (texturing).…”

“…However, the high piezoelectricity of these materials originates from the enhanced polarizability associated with the compositional shift of the orthorhombicto-tetragonal polymorphic phase transition (PPT) from 195 1C for pure KNN 275 downward to room temperature. 271,272 This inevitably leads to temperature-dependent properties and partial depoling of the ceramics by thermal cycling through the PPT. 271,276 The interest in KNN has been recently revived by the discovery of the excellent functional properties of the niobate sintered in reducing atmosphere.…”

Unusual Phase Behavior in the Piezoelectric Perovskite System, LixNa1–xNbO3

“…1 A leading candidate amongst a range of promising materials is the solid solution KNN (K x Na 1-x NbO 3 ). 2,3 Sodium niobate (NaNbO 3 ) itself is an intriguing material, with perhaps one of the most complex temperature-dependent phase diagrams amongst simple perovskites. 4 , 5 , 6 Although itself antiferroelectric (orthorhombic, Phase P, space group Pbcm) at ambient temperature, NaNbO 3 becomes ferroelectric (rhombohedral, Phase N, space group R3c, Glazer tilt system 7 a -a -a -) below 173 K. Depending on sample synthesis conditions, a ferroelectric polymorph, Phase Q (orthorhombic, space group P2 1 ma, Glazer tilt system a -b + a -) can co-exist with Phase P at room temperature.…”

“…4 , 5 , 6 Although itself antiferroelectric (orthorhombic, Phase P, space group Pbcm) at ambient temperature, NaNbO 3 becomes ferroelectric (rhombohedral, Phase N, space group R3c, Glazer tilt system 7 a -a -a -) below 173 K. Depending on sample synthesis conditions, a ferroelectric polymorph, Phase Q (orthorhombic, space group P2 1 ma, Glazer tilt system a -b + a -) can co-exist with Phase P at room temperature. 8,9 Moreover, the orthorhombic ferroelectric phase of NaNbO 3 can be made via chemical doping; indeed doping as little as 2% of either potassium or lithium, to form the solid solutions K x Na 1-x NbO 3 or Li x Na 1-x NbO 3 , induces both a change in the octahedral tilt system of Phase P and a polarization to produce Phase Q. 10 The composition-dependent phase diagram of KNN has recently been re-analysed and is now fairly well understood, 11,12 but that of LNN has received much less attention.…”

(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics Synthesized by a Gel-Casting Method

“…Therefore, a continual search for a more environmentally friendly piezoelectric materials is carried out around the world, particularly as the European Union issued a directive that limits the potential use of PZT in applications. 4 (Ba 0.85 Ca 0.15 ) (Zr 0.1 Ti 0.9 )O 3 (BCZT) is a type of lead-free material with a perovskite structure. Compared with many other lead-free candidates which possess a low piezoelectric coefficient (d 33 ), such as bismuth sodium titanate (BNT; d 33 = 64 pC/N) 5 and CuOadded KNbO 3 (xCKN; d 33 = 65-110 pC/N).…”