Aurivillius oxides family has attracted great interest in the last years due to their promising electrical properties as high temperature piezoelectric materials. Piezoelectric materials that could operate in extreme conditions of use (elevated temperatures and hostile environments) could be of particular interest for different technological applications. Furthermore, increasing concerns for environmental issues have promoted the study of new lead-free piezoelectric materials. This article examines how the development of these materials has taken place from their discovery at the end of the 40's and the existing knowledge about their processing and properties.

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SiC fabric with or without alumina powder was joined to the surfaces of SiC compact under the applied pressures of 5-39 MPa. The stress-strain curve, strength, damage tolerance using Vickers indentor and crack healing effect were investigated for both the SiC with and without SiC fabric layers. The strength of monolithic SiC was greatly decreased by the surface damage but easily recovered to the original strength by the healing at a relatively low temperature of 1100°C in air. When a simultaneous processing using an SiC compact covered with SiC fabric was applied, which promoted the densification of inside SiC compact, the surface SiC fabric dissolved in the liquid of sintering additives included in the SiC compact during the hot-pressing at 1950°C. The mechanical properties of this type composite were similar to those of monolithic SiC compact. The SiC fabric joined to dense SiC compact under a low applied pressure at 1300-1600°C prevented the propagation of the cracks formed by Vickers indentor and showed a significant nonlinear stress-strain curve. As a result, no change in the strength was measured before and after the introduction of cracks. However, increased joining pressure resulted in the creep rupture of dense inside SiC compact. Decrease of the joining temperature and decrease of the joining pressure were effective to increase the flexural strength.

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To investigate the defect structure of Zn_2-x/2Ti_1-xTa_xO₄ and the subsequent oxide ion conduction, equimolar Al³⁺ with Ta⁵⁺ have been partly substituted instead of Ti⁴⁺ ions in Zn₂TiO₄, forming Zn₂Ti_1-2xTa_xAl_xO₄ with no significant cation vacancy despite of tantalum substation. Inverse spinel-type structured solid solution was approximately formed up to x = 0.3 and the measured powder density agreed with the nominal model where all the cation sites ware almost occupied. A slight decrease in oxide ion conductivity was observed for Zn₂Ti_1-2xTa_xAl_xO₄ with the dual substitution by x, while apparent increase for Zn_2-x/2Ti_1-xTa_xO₄, indicating that the cation vacancy is responsible for the oxide ion conduction in Zn₂TiO₄-based system. Powder neutron diffraction revealed the defect structure, which were then discussed in terms of the oxide ion conduction mechanism with the deduced isotropic temperature factors of oxide ions.

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Ultraviolet (UV) light was irradiated in air for 1 h on titania (rutile) films prepared by thermal oxidation of titanium substrates from 300°C up to 800°C, coded as HT300UV, HT400UV, HT500UV, HT600UV, HT700UV, and HT800UV, respectively. All samples were then soaked in a simulated body fluid (SBF, Kokubo solution) and their in vitro apatite-forming ability was evaluated. It was found that bone-like apatite particles were deposited on HT500UV, HT600UV, and HT700UV within 7 d whereas that was not the case with others during the same period. Moreover, the apatite particles were deposited more on HT500UV than on the others. Therefore, the ultraviolet light irradiation enhanced the in vitro apatite-forming ability of the thermally oxidized titanium.

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(K_0.52Na_0.48)_1-xLi_x (Nb_1-xSb_x)O₃ lead-free ceramics were prepared by solid state reaction and the electrical properties of the ceramics were characterized. The crystalline phases and microstructure of the ceramics exhibit much dependence on the content of x, and the orthorhombic and tetragonal phases of the samples coexisted in the composition range of 0.04 ≤ x ≤ 0.05 at room temperature. The ceramics with x = 0.05 show the better die-, piezo- and ferroelectric properties: piezoelectric constant d₃₃ = 303 pC/N, planar electromechanical coupling coefficient k_p = 0.50, the relative dielectric constant K = 1228, syntonic impedance R_r = 66.1Ω, remnant polarization P_r = 31.2 μC/cm², and coercive field E_c = 0.770 kV/mm.

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Magnetoelectric laminated composites of a length-magnetized magnetostrictive Tb_0.3Dy_0.7Fe_1.92 (Terfenol-D) alloy plate sandwiched between two thickness-polarized, electro-parallel-connected piezoelectric 0.7Pb (Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) single crystal plates were fabricated and their converse magnetoelectric properties were evaluated. An electromagnetic control device using a laminated composite as the control element and an Alnico biasing magnet, two Mn-Zn F-yokes and a Mu-metal movable plate as the magnetic circuit was developed and characterized. The distribution of the dc magnetic flux lines and magnetic inductions of the device were analyzed using a finite element method. The quasistatic and dynamic magnetic inductions of the device were measured, together with the generative forces. The results revealed that the device has linear voltage-controlled magnetic inductions in excess of 0.6 G/V with flat responses in the measured frequency range of 0.1-40 kHz and large generative forces over 0.7 N at 160 V at the designated gaps of 1.0-1.2 mm. This coil-free device could be useful in broadband and precision magnetic flux/force control applications with negligible Joule heating losses.

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Microwave dielectric properties of MgB₂O₆ (B⁵⁺ = Nb, Ta, Sb) and their solid solutions have been investigated to control the temperature coefficient of resonant frequency (TCF) of MgTa₂O₆ ceramics. At the composition range of single phase, TCF of the sintered specimens was depended on the distortion of oxygen octahedra by the substitution of Nb and/or Sb for Ta of MgTa₂O₆. For the Mg(Ta_1-xNb_x)₂O₆ (0.2 ≤ x ≤ 0.8) and Mg(Ta_1-xSb_x)₂O₆ (0.1 ≤ x ≤ 0.4) sintered specimens, the quality factor (Qf) was decreased with x content. The dielectric constant (K) of the sintered specimens was dependent on the dielectric polarizabilities.

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For the integration of multi-chip module required thermally stable epoxy adhesive, the effects of clay incorporation on the thermal stability of cured epoxy adhesive were investigated. Various epoxy adhesives were prepared as a function of a number of epoxy rings and the amount of hardener. Based on the relationship between the glass transition temperature (T_g) and cross-linking density obtained from the curing mechanism analyzed by FT-IR, the epoxy adhesive with T_g higher than 200°C was synthesized by raising cross-linking density to the maximum. With the incorporation of clay, the curing reaction rate and the degradation of epoxy adhesive can be controlled. The epoxy/clay composite showed the higher height of tanδ peak than that of pure epoxy adhesive.

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We investigated photoelectrochemical behavior of rhodamine 6G (R6G) dye intercalated in layered oxides of semiconducting hexaniobate and photochemically inert saponite clay. The R6G-clay intercalation compound generated comparable cathodic and anodic photocurrents. Photocurrent action spectra indicated that both the photocurrents were ascribed to photoexcitation of R6G monomers and dimers present in the interlayer spaces. On the other hand, the R6G-niobate intercalation compound exhibited a relatively large cathodic and small anodic photocurrents. Action spectra of the R6G-niobate system indicated that the photocurrents were generated by photoexcitation of only the R6G monomers while that the coexisting dimeric species were apparently silent. This result was explained by that the photocurrents were generated through photosensitization of the photocatalytically active semiconducting niobate layers with electron transfer from the photoexcited R6G monomers, whereas that the dimers were deactivated through dye-dye interactions.

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We have developed borosilicate glasses with high softening points for glass-ceramic / copper multilayer substrates. The softening points of this glass ranged from 900°C to 1000°C. Glass-ceramics made using this glass barely sintered below 850°C, but sintered compactly at temperatures just below 1050°C. Green sheets made using this glass-ceramics could be fired around 850°C to remove the binder. Binder removal was caused very fast at this temperature. The glass-ceramics could be co-sintered with copper and had various advantages, such as easy binder removal, a coefficient of thermal expansion approximately equal to that of silicon, a low dielectric constant, sufficient flexural strength, and high water durability. These advantages helped make the manufacturing process of the substrate more productive.

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Electrical resistivity of AlN ceramics was examined with various amounts of Y₂O₃ within 0 to 4.8 mass%. The electrical resistivity at room temperature varied from 10¹⁶ to 10¹⁰ Ω·cm with different Y₂O₃ amounts and at sintering temperatures. In the typical samples sintered at 1900°C, a smaller amount of Y₂O₃ addition with 0.1 to 0.5 mass% gives the lowest electrical resistivity of 10¹⁰ Ω·cm, whereas the higher amount of Y₂O₃ maintains high resistivity of more than 10¹³ Ω·cm. The results derived from different analytical techniques such as impedance analysis, cathodoluminescence spectrum and microstructural analysis explain the importance of the oxygen concentration in the AlN grain for the electrical resistivity of AlN ceramics.

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Solid-state reactive sintering a stoichiometric mixture of commercial γ-Al₂O₃, Y₂O₃, Nd₂O₃ and Cr₂O₃ powders was conducted at 1800°C with tetraethoxysilane (TEOS) as sintering aid and CaO as charge compensator. The cubic garnet structure of YAG (Y₃Al₅O₁₂) as well as orthorhombic structure of YAP (YAlO₃) formed in the sample due to mass loss of γ-Al₂O₃ during sintering. The sample obtained was fully dense but not transparent and the width of grain boundary phase was about 300 nm contained a significant amount of Si and Nd, compared with the inner grains. The doping concentration of Nd and Si in YAlO₃ phase is much larger than that in Y₃Al₅O₁₂ phase. However, when a little more γ-Al₂O₃ than stoichiometric composite was added, transparent Cr,Nd:YAG ceramic could be obtained. The optical transmittance of the sample sintered at 1800°C for 10h is 68.5% at 1064nm and the average grain size is about 10 μm.

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We prepared two new water-soluble complexes of titanium with L-serine and L(-)-threonine amino acids. It was demonstrated that these compounds can be outstanding precursors for a hydrothermal synthesis of nanocrystalline TiO₂. The obtained powders were composed of anatase or a mixture of anatase and brookite. Particles diameters were ~10 nm and BET surface areas were ~120 m²/g. The powder composed of anatase and brookite synthesized by hydrothermal treatment of the titanium-threonine complex aqueous solution at 200°C for 24 h exhibited higher photocatalytic activity for oxalic acid oxidation than the commercial anatase-type TiO₂ photocatalyst (ST-01, Ishihara Sangyo Kaisya, average diameter: 7 nm, specific surface area: 257.5 m²/g).

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Fine-sized BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu) phosphor powders with regular morphology were prepared by flux-assisted spray pyrolysis. The precursor powders with hollow structure and large size obtained by spray pyrolysis were mixed with aluminum fluoride flux. The post-treated BAM:Eu phosphor powders had fine sizes, narrow size distributions, and plate-like morphologies without milling process. The mean size of the BAM:Eu phosphor powders obtained from the optimum amount of aluminum fluoride flux was 1.1μm. The photoluminescence intensity of the phosphor powders obtained from the precursor powders without flux was 84% of that of the commercial phosphor powders. On the other hand, the photoluminescence intensities of the phosphor powders obtained from the precursor powders with 3 and 5 mass% aluminum fluoride flux were each 90% and 93% of that of the commercial phosphor powders.

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The electronic structure of antiferromagnetic Bi₂CuO₄ is calculated by using generalized gradient approximation considering on-site Coulomb interaction between d-electrons (GGA+U). The GGA+U calculation indicates clearly that the antiferromagnetic phase is the stablest among non-magnetic, ferromagnetic and antiferromagnetic phases. By using U parameter (7.48 eV) and J parameter (0.95 eV), the band gap energy of Bi₂CuO₄ is calculated to be ca. 2.4 eV, which is comparable to the experimental one. The valence band maximum is approximately located at the X-point and the conduction band minimum at the Γ-point. This means that antiferromagnetic Bi₂CuO₄ is an indirect energy gap material. The calculated total density of states of Bi₂CuO₄ well corresponds to the state density experimentally deduced by x-ray photoelectron and electron-energy-loss spectroscopy. Also, it is found from the partial density of states analysis that the top of the valence band is mainly formed by O 2p orbitals, whereas the lower conduction band mainly consists of Cu 3d_x²_-y² orbitals. The magnetic moment at Cu sites is calculated to be 0.72 μ_B, which is close to experimental values.

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