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

Muon spin rotation-relaxation (SR) spectroscopy has been used to investigate the magnetic properties of polycrystalline Ca 3Ϫx M x Co 4 O 9 (xр0.5,M ϭSr,Y, and Bi͒ and Na 0.7 CoO 2 samples in the temperature range between 2.5 and 300 K. It was found that Ca 3 Co 4 O 9 exhibits a magnetic transition at around T c ϭ100 K; at lower temperatures, two types of relaxation were observed using a weak transverse field SR technique with Hϭ104 Oe: one with a fast relaxation rate F ϳ10 s Ϫ1 and the other with a slow S ϳ0.1 s Ϫ1 . Zero-field SR measurements suggest the existence of an incommensurate spin-density-wave ͑SDW͒ state below T c ͑i.e., T c ϭT SDW ), although a ferrimagnetic M -H loop was observed by a dc susceptibility measurement below 19 K. The substitution of Y or Bi for Ca increased T SDW , while the substitution of Sr for Ca did not affect T SDW . This indicates that the SDW transition depends strongly on the average valence of the Co ions. The related material Na 0.7 CoO 2 showed no magnetic transitions below 30 K. Considering the difference between the crystal structures of Ca 3 Co 4 O 9 and Na 0.7 CoO 2 , we suggest that Co ions in the rocksalt-type layers of Ca 3 Co 4 O 9 are likely to play a significant role in inducing the SDW transition around 100 K.

Textured bulk ceramics have been prepared of various cobaltites including the common CdI 2 -type CoO 2 layer (i.e., [Ca 2 (Co 0.65 Cu 0.35 ) 2 O 4 ] 0.624 [CoO 2 ]: CCO-4-layer, [Bi 2 M 22x O 4 ] p [CoO 2 ] (M 2 ~Sr 2 : BSCO, M 2 ~Ca 1 Sr 1 : B(SC)CO, M 2 ~Ca 2 : BCCO)) by using b-Co(OH) 2 (CdI 2 -type) platelets as reactive templates, and their thermoelectric (TE) properties have been examined. All the specimens were found to be highly c-axis aligned ceramics. Especially for CCO-4-layer, B(SC)CO and BCCO, the present study is the first report on the fabrication of textured ceramics. Our textured ceramic specimens exhibited larger values of electrical conductivity (s) than the ceramics prepared by a conventional solid-state reaction (SSR specimens): e.g., s ab ~0.46 6 10 4 S m 21 for the textured specimen and s SSR ~y0.26 6 10 4 S m 21 at 1060 K for the SSR specimen for BCCO. This study indicated that our preparation method using b-Co(OH) 2 templates is a versatile and effective technique to fabricate cobaltites, including CoO 2 layers, with a high degree of orientation and improved TE properties.

Dense CaBi4Ti4O15 (CBT) and Na0.475Ca0.05Bi4.475Ti4O15 (NCBT) ceramics with a highly preferred {001} orientation were prepared by the reactive templated grain growth (RTGG) method. Plate-like Bi4Ti3O12 (BIT) particles were synthesized by a molten salt technique and used as the reactive template. The template particles were mixed with other oxide and carbonate powders and aligned by tape-casting. During the sintering, oriented CBT and NCBT were formed in situ topotaxially on the oriented BIT particles, and textured CBT and NCBT ceramics were eventually fabricated by the templated grain growth and densification. The Lotgering {001} orientation degree of the textured ceramics exceeded 90% for secondary-laminate sintered specimens. Textured CBT and NCBT ceramics poled in the perpendicular direction to the preferred <001> axis exhibited electromechanical coupling coefficient (k 33) and piezoelectric coefficients (d 33 and g 33) three times higher than the values for nontextured ceramics with the same composition.