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 <001> 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.

O 3 polycrystals exhibit piezoelectric properties comparable to those of lead zirconium titanate ceramics which are high-performance piezoelectric materials. The properties of the Pb-free piezoelectric ceramic are due to the existence of a morphotropic phase boundary in the alkaline niobate-based perovskite solid solution. It is expected that the new material is a leading candidate for environmentally friendly piezoelectric devices. -(SAITO, Y.; TAKAO, H.; TANI, T.; NONOYAMA, T.; TAKATORI, K.; HOMMA, T.; NAGAYA, T.; NAKAMURA, M.; Nature (London, UK) 432 (2004) 7013, 84-87; Toyota Cent. Res. Dev. Lab., Nagakute, Aichi 480-11, Japan; Eng.) -W. Pewestorf 03-016

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The microstructural development of crystalline-oriented (K 0.5 Na 0.5 )NbO 3 (KNN)-based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens containing 0.5-1.0 mol% CuO sintered at 11001C for 1 h were found to have relative densities and pseudo-cubic {100} orientation degrees of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO 3 and KNbO 3 , after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of transmission electron microscopy observation showed that textured KNN ceramics have a unique pectinate-like domain structure with domain walls consisting of {101} planes. 1951J ournal

Polycrystalline rectangular-platelike KNbO 3 particles with an orthorhombic perovskite structure were synthesized by the topochemical microcrystal conversion (TMC) method from rectangular-platelike precursor particles of layer-structured K 4 Nb 6 O 17 at 850 • C in molten KCl-salt. TMC-synthesized KNbO 3 particles preserved the shape of precursor particles, and had a thickness of about 1 m, a width of 5-10 m and a length of 20-40 m. However, TMC-synthesized rectangular-platelike KNbO 3 particles exhibited a polycrystalline morphology having preferred pseudo-cubic {0 0 1} orientation. Oriented particulate layer (OPL) X-ray diffraction analysis revealed that, in the TMC reaction, the crystallographic {0 1 0} plane of K 4 Nb 6 O 17 , which is the largest extensive face, is converted into the {0 0 1} plane of polycrystalline KNbO 3 particles, which is the largest developed face, in spite of polycrystalline morphology. Using the polycrystalline rectangular-platelike KNbO 3 particles as template in the reactive templated grain growth method, grain-oriented (K 0.5 Na 0.5 )NbO 3 -1 mol% CuO ceramics having a pseudo-cubic {0 0 1} orientation degree (Logering's factor) of 39.7% could be fabricated. The result indicates that not only single crystalline particles, which were generally used, but also the polycrystalline particles can be act as template in the templated grain growth process. The availability of polycrystalline particles will give a new synthesis design of templates for texturing of various kinds of ceramics.