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

We report a non-Pb piezoelectric ceramic system Ba(Ti(0.8)Zr(0.2))O(3)-(Ba(0.7)Ca(0.3))TiO(3) which shows a surprisingly high piezoelectric coefficient of d(33) approximately 620 pC/N at optimal composition. Its phase diagram shows a morphotropic phase boundary (MPB) starting from a tricritical triple point of a cubic paraelectric phase (C), ferroelectric rhombohedral (R), and tetragonal (T) phases. The high piezoelectricity of the MPB compositions stems from the composition proximity of the MPB to the tricritical triple point, which leads to a nearly vanishing polarization anisotropy and thus facilitates polarization rotation between 001T and 111R states. We predict that the single-crystal form of the MPB composition of the present system may reach a giant d(33) = 1500-2000 pC/N. Our work may provide a new recipe for designing highly piezoelectric materials (both Pb-free and Pb-containing) by searching MPBs starting from a TCP.

Large Piezoelectric Effect in Pb-Free Ceramics

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?

Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature.

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Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

Lead has recently been expelled from many commercial applications and materials (for example, from solder, glass and pottery glaze) owing to concerns regarding its toxicity. Lead zirconium titanate (PZT) ceramics are high-performance piezoelectric materials, which are widely used in sensors, actuators and other electronic devices; they contain more than 60 weight per cent lead. Although there has been a concerted effort to develop lead-free piezoelectric ceramics, no effective alternative to PZT has yet been found. Here we report a lead-free piezoelectric ceramic with an electric-field-induced strain comparable to typical actuator-grade PZT. We achieved this through the combination of the discovery of a morphotropic phase boundary in an alkaline niobate-based perovskite solid solution, and the development of a processing route leading to highly textured polycrystals. The ceramic exhibits a piezoelectric constant d33 (the induced charge per unit force applied in the same direction) of above 300 picocoulombs per newton (pC N(-1)), and texturing the material leads to a peak d33 of 416 pC N(-1). The textured material also exhibits temperature-independent field-induced strain characteristics.

Lead-free piezoceramics

The present invention provides crystal oriented ceramics, and a production method of the same, having a basic composition of isotropic perovskite-based potassium sodium niobate, demonstrating superior piezoelectric characteristics, and having a specific crystal plane oriented to a high degree of orientation. The crystal oriented ceramics as claimed in the present invention is composed of a polycrystalline substance of an isotropic perovskite compound represented by the general formula: {Li x (K 1-y Na y ) 1-x }{Nb 1-z-w Ta z Sb w }O 3 (wherein, 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 1, 0 ≤ z s 0.4, 0 s w ≤ 0.2, x + z + w > 0), and a specific crystal plane of each crystal grain that composes said polycrystalline substance is oriented. 
Such crystal oriented ceramics are obtained by molding a mixture of a first anisotropic shaped powder, for which the growth plane has lattice coherency with a specific crystal plane of the isotropic perovskite compound to be produced, and a first reaction raw material, so that the first anisotropic shaped powder is oriented, followed by heating.

Crystal oriented ceramics and production method of same

To provide a grain oriented ceramic capable of exerting excellent piezoelectric properties, a production method thereof, and a piezoelectric material, a dielectric material, a thermoelectric conversion element and an ion conducting element each using the grain oriented ceramic, there is provided a grain oriented ceramic comprising, as the main phase, an isotropic perovskite-type compound which is represented by formula (1): {Lix(K1−yNay)1−x}(Nb1−z−wTazSbw)O3 in which x, y, z and w are in respective composition ranges of 0≦x≦0.2, 0≦y≦1, 0≦z≦0.4, 0≦w≦0.2 and x+z+w>0. The main phase comprises a polycrystalline body containing from 0.0001 to 0.15 mol of any one or more additional element selected from metal elements, semimetal elements, transition metal elements, noble metal elements and alkaline earth metal elements belonging to Groups 2 to 15 of the Periodic Table, per mol of the compound represented by formula (1). A specific crystal plane of each crystal grain constituting said polycrystalline body is oriented.

Grain oriented ceramics and production method thereof

PROBLEM TO BE SOLVED: To provide a crystallographic orientation ceramic which can demonstrate excellent piezoelectric characteristics, and its manufacturing method, as well as a piezoelectric material using the crystallographic orientation ceramic, a dielectric material, a thermoelectric element, and an ionic conductive element. SOLUTION: The crystallographic orientation ceramic has as the main phase an isotropic perovskite compound represented by general formula (1): aLi x (K 1-y Na y ) 1-x }(Nb 1-z-w Ta z Sb w )O 3 , wherein x, y, z and w are each within the composition range of 0≤x≤0.2, 0≤y≤1, 0≤z≤0.4, 0≤w≤0.2, and x+z+w>0, respectively. The main phase consists of a polycrystal containing one or more kinds of additive elements of 0.0001-0.15 mol selected from among a metallic element belonging to group II-XV in the periodic table, a metalloid element, a transition metal element, a noble metal element, and an alkaline earth metal element to a compound represented by general formula (1) of 1 mol. Specific crystal faces of each crystal grain composing the polycrystal are oriented. COPYRIGHT: (C)2006,JPO&NCIPI

Crystallographic orientation ceramic, and its manufacturing method

To provide a production method of a polycrystalline ceramic body with excellent density, a preparation step, a mixing step, a forming step and a heat-treating step are performed. In the preparation step, a coarse particle ceramic powder, and a fine particle powder having an average particle diameter of ⅓ or less of the average particle diameter of the coarse particle ceramic powder are prepared. In the mixing step, the coarse particle ceramic powder and the fine particle powder are mixed to produce a raw material mixture. In the forming step, the raw material mixture is formed to a shaped body. In the heat-treating step, the shaped body is heated and thereby sintered to produce a polycrystalline ceramic body. In the heat-treating step, a temperature elevating process and a first holding process are performed and at the same time, a second holding process and/or a cooling process are performed. In the temperature elevating process, heating is started to elevate the temperature and in the first holding process, the shaped body is held at a temperature T1° C. In the second holding process, the shaped body is held at a temperature T2° C. lower than the temperature T1° C. In the cooling process, the shaped body is cooled at a temperature dropping rate of 60° C./h or less from the temperature T1° C.

Masaya Nakamura

Papers

Lead-free piezoceramics

Crystal oriented ceramics and production method of same

Grain oriented ceramics and production method thereof

Crystallographic orientation ceramic, and its manufacturing method

Production method of polycrystalline ceramic body