Recent research activities of the author's group concerning the structure-property relationship and property design by defect control of bismuth layer-structured ferroelectrics (BLSFs) are described. The polarization measurements for various single-crystal BLSFs showed that the remanent polarization P_r and the coercive field E_c of these ferroelectrics are related to Curie temperature and the number of perovskite units in one layer, m, respectively. For SrBi₂Ta₂O₉ (SBT), Bi substitution at the A site increased P_r, and rare-earth-element substitution at the A site decreased or increased E_c depending on the type and amount of rare-earth element used. These property changes were due to changes in lattice distortion induced by the substitution, and the softening and hardening of polarization property were attained in SBT. A decrease in the concentration of oxygen vacancies was found to be very effective in improving the polarization and insulating properties of Bi₄Ti₃O₁₂ (BIT). Conductivity analysis and ab initio band-structure calculations showed that the doping of higher-valence cations at the B site and the substitution of rare-earth elements for Bi at the A site decrease the concentration of oxygen vacancies, which cause domain pinning, by charge compensation and lattice stabilization, respectively. Such defect control was demonstrated to be a promising approach to designing the polarization properties of BLSFs.

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Unstabilized and yttria stabilized ZrO₂ fibers were prepared from a monodispersed ZrO₂ particles derived from hydrolysis of Zr(OBu)₄. Unstabilized ZrO₂ fibers with 71 to 151 μm of width and yttria stabilized ZrO₂ fibers with 96 to 214 μm of width, were formed by drying the ethanol suspension of monodispersed ZrO₂ particles with 116 nm in mean diameter. The morphology of the ZrO₂ fibers were plate like and consisted of densely packed ZrO₂ nano particles. The preparation conditions affected the fiber width. This was due to the lower concentration of ZrO₂ particles in suspension, or the higher drying temperatures, which gave the narrower fiber width. The mean particle size of the 5 mol% Y₂O₃ doped ZrO₂ fiber heat treatment at 1473 K was 0.14 μm and the fiber showed 11.0 GPa on the Vickers Hardness Test.

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Oxidation behavior of MgO-based composites with 5 vol% Ni particle dispersoid was investigated at temperatures ranging from 1100 to 1300°C in air. Oxidized zone consisted of (Mg, Ni)O solid solution and included voids. Growth kinetics of the oxidized zone followed a parabolic law, which meant that mass transport in the oxidized zone was the rate-controlling process. An oxidation model of Ni-dispersed MgO composites was established as a basis of cation diffusion via vacancy diffusion with defect chemistry of formation of cation vacancy in the MgO-NiO system. The parabolic rate constant and its apparent activation energy estimated from the proposed model agreed with experimental results.

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The changes in microstructure and properties of ZnO-added alumina upon sliding under water lubrication were studied. Although the frictional force was lower than that of conventional alumina in the early stages, it increased upon long-term friction testing. Of the acicular ZnO-nAl₂O₃ (n=3-9) and granular ZnAl₂O₄ phases dispersed in the samples, ZnAl₂O₄ with its low hardness was worn preferentially and pulled out during testing. The increase of frictional force during the sliding process was attributed to the pull-out of ZnAl₂O₄ particles and their traction on the sliding surface during the experiment.

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The ferroelectric PbTiO₃ (PT) thin films were deposited on MgO(100) and Si(001) substrates by Liquid Source Mist Chemical Vapor Deposition (LSMCVD) method. The Pb(DPM)₂ and Ti(iOC₃H₇)₄ (TTIP) were used as metal sources. Metal-organic sources were dissolved in 2-metoxyethanol. The PT thin films have (h00) and (00l) preferred orientations at lower metal source concentrations on MgO(100) substrate. The epitaxial PT thin film could be prepared on MgO(100) substrate at 0.02 mol/L solution at 600°C. The epitaxial PT thin films having stoichiometric composition and smooth surfaces were prepared on MgO(100) substrates. In this study, the solution concentration is an important process parameter to fabricate epitaxial PT thin films. The PT thin films which have polycrystalline phases on Pt(111)/TiO₂/SiO₂/Si(001) showed about 320 of dielectric constants and 3uC/cm² of remanent polarization with 109.54 kV/cm of coercive field.

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The phase transition of Zr_1-xHf_xV₂O₇ (x=0-1) solid solutions substituted for Zr(IV) sites was investigated using X-ray diffraction, TMA and DSC methods. X-ray diffraction experiments revealed that all compositions of Zr_1-xHf_xV₂O₇ (x=0-1) were of a single phase having a cubic structure. Lattice parameters of Zr_1-xHf_xV₂O₇ (x=0-1) at room temperature decreased linearly with increasing Hf content, due to the smaller ionic radius of the Hf(IV) ion than that of the Zr(IV) ion. Abrupt positive thermal expansions in TMA were observed for all samples at two phase transition temperatures in the vicinity of T₁=350 K and T₂=375 K, and negative thermal expansions were seen above about 380 K. DSC measurements clearly showed that all of the Zr_1-xHf_xV₂O₇ (x=0-1) samples also underwent two successive phase transitions between 330 and 390 K. Two transition temperatures and phase transition enthalpies of Zr_1-xHf_xV₂O₇ (x=0-1) samples decreased with the increase of x content, reflecting the decrease of superlattice structure. The sum of transition entropy for successive two phase transitions increased with increasing the normalized relative intensity of the superlattice line at room temperature.

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The dielectric temperature characteristics of the high-k (Ba_1-xLa_x)(Ti_1-x/4-0.05Ce_0.05)O₃ ceramics (BLTC: where x=0.01 to 0.05) with diffuse phase transition (DPT) behavior at different frequencies were studied. The ‘relaxor’ behavior of BLTC with respect to temperature (at 1 kHz) and frequency was quantified by means of some parameters, FWHM, δ, γ, and ΔT_mf′, Δε_mf′/ε_m′, repectively. DPT behavior and thermal hysteresis effect were discussed. The results indicated that the co-doping with La and 5 at% Ce causes strong diffusion of ferroelectric phase transition of BaTiO₃ and pronounced rising of the permittivity peak (ε_m′>10000 for 0.02≤x≤0.05) in a frequency range 1 to 100 kHz. The rate that the permittivity peak shifts towards low temperature decreases slightly with increasing frequency, from 30.7°C/at% La at 1 Hz to 29.5°C/at% La at 100 kHz. This rate is faster than any BaTiO₃ dopant reported previously. The x=0.03 sample meets Y5V and Z5U specifications at 1 kHz when the thermal hysteresis effect is considered. The increase in La concent (x) can markedly suppress the dielectric loss (tan δ).

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Recently, the development of new nonsulfide phosphors with high efficiency is urgently needed for VFDs and FEDs. The fabrication for hexagonal Zn_1-x Mg_xO (0.0≦x≦0.15) solid solution and the effect of partially substituted MgO on the cathode luminescence (CL) were investigated in this research. A limited range of (Zn_1-xMg_x)O solid solution was prepared using the thermal decomposition of complex Zn-Mg oxalate. The solubility of Mg in ZnO was estimated to be ca. 15%. In the samples annealed at 1373 K for 2 h in a reduced atmosphere, green to blue cathode luminescence was observed. It is evident that the partial substitution of MgO results in the shift of green emission band at low wavelength side. The CL material is expected as a low-cost and blue light-emitting phosphor for lowvoltage luminescence in flat panel displays.

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Silicate gels were prepared by mixing K₂O•3.9SiO₂ (0.3 mol/L) and Al(NO₃)₃•9H₂O (1 mol/L) solutions in various ratios, using potassium hydroxide solution (1 mol/L) to regulate the pH. Nine gel samples were thus prepared at a range of pH conditions, filtered, washed and air-dried. About 1 mol% of potassium was incorporated into the gels at low pH, but up to 20 mol% was incorporated under high pH conditions. On heating, characteristic DTA exotherms were observed at higher temperatures, possibly providing an indication of the degree of polymerization of the gels. The low-potassium gels exhibited a sharp exothermic peak at about 1000°C corresponding to mullite formation, whereas the high-potassium gels exhibited a small, gentle exotherm at about 1000-1100°C corresponding to the formation of KAlSiO₄ (PAS, considered to be one of the modifications of kalsilite) and/or KAlSi₂O₆ (leucite), depending on the gel composition. The ²⁹Si and ²⁷Al MAS-NMR spectra showed that the potassium-poor gels contain predominantly tetrahedral Si(1-2Al) and Q1 silicate units, and both tetrahedral and octahedral Al³⁺, whereas the potassium-rich gels contain predominantly Si(4Al) units and solely tetrahedral Al³⁺. The implications of these results for the formation of potassium geopolymers are discussed.

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We investigated the relation between the crystal structure and ferroelectric properties of Bi₂SiO₅, Bi₄Si₃O₁₂ and Bi₂O₃-added Sr_0.8Bi_2.2Ta₂O₉. Moreover, we investigated that the effect of heat treatment using one of the Bi₄Si₃O₁₂ added Sr_0.8Bi_2.2Ta₂O₉ compounds after a vacuum and high pressure oxygen treatment. The remanent polarization(P_r) increased with the added Bi₄Si₃O₁₂ or Bi₂O₃, however, it decreased due to added Bi₂SiO₅. It was considered that the volume of the tetrahedrons, which makes the top of Bi, increased with the addition of Bi₂O₃ in the (Bi₂O₂)²⁺ layer, and the displacement of the atom becomes easy for the applied field due to the pseudo perovskite (SrTa₂O₇)^2- received stress. It was noted that the T_c decreased with the decreasing tilting angle(α_b) of the TaO₆ octahedron by heat treatment of the reduced direction.

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We established a quantitative analytical method of nanoparticle dispersibility, which includes the following steps; 3D reconstructed image by TEM-CT, particle separation by 3D image analysis, and calculation of a dispersibility index. First the 3D image was reconstructed by a series of 121 projections collected along a single tilt axis on TEM. Second particles were separated from the reconstructed image by binarization. The distance between the gravity centers of particles was measured from the reconstructed images. Finally a dispersibility index was defined as the average of the shortest distances for adjacent nanoparticles divided by an ideal distance. The proposed method was applied for alumina nanoparticles in polymer nanocomposites under different synthetic processes, and the dispersibility of them was calculated by the index. The correlation between the dispersibility as a structure and the transmittance at 700 nm as a function was found to be linear. This method is applicable to evaluate the 3D dispersibility quantitatively for the nanoparticle arrays.

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The viscoelastic properties of phosphate and borate glasses at and below the transition temperature (T_g) were investigated using the dynamic viscoelastic measuring method. The viscosity in these glasses was found to increase with decreasing temperature, from 10¹² Pa•s at T_g to between 10¹⁵-10¹⁶ Pa•s at around 50°C. The free volume-viscosity relation in glass is discussed considering the free volume theory as applied to polymers. As a result, the free volume was found to be applicable to glass at below T_g. But in contrast to polymers, the free volume fraction was found to differ from one glass to another. Glass structure and bond strength are believed to affect the free volume fraction.

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Reactivity of the mixed powder of Li₂CO₃ with several metal oxides (Y₂O₃, Al₂O₃, ZrO₂, SiO₂ and ZrSiO₄) in synthetic air and 100%CO₂ was examined to develop a high temperature repeatable CO₂ absorbent. The mixture of Li₂CO₃ and Y₂O₃ in molar ratio of 1 : 1 was stable in CO₂ up to 950°C but decomposed to form LiYO₂ at around 850°C in synthetic air (N₂ 79%+O₂ 21%, CO₂<0.5 ppm). The newly formed LiYO₂ started to absorb the CO₂ at 300°C with the reaction of 2LiYO₂+CO₂→Li₂CO₃+Y₂O₃. Since the mixture was fairly stable in CO₂ up to 980°C, the reversed reaction directed to CO₂ emission was not observed in CO₂. LiYO₂ is a new material for a CO₂ absorbent available in a wide range of temperature.

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The novel hydrothermal synthesis assisted with ball milling during hydrothermal treatment was developed. Barium titanate (BaTiO₃) powder prepared by this method and the effect of the ball milling was evaluated. The starting materials were sub-micron sized TiO₂ powder and Ba(OH)₂. The synthesized BaTiO₃ powders were characterized by X-ray diffraction (XRD), a laser scattering particle size distribution analyzer and a field emission scanning electron microscopy (FE-SEM). The XRD patterns showed that the BaTiO₃ powders were synthesized at 100°C and for 5 h with little contamination. The present BaTiO₃ powders observed by FE-SEM were regularly agglomerated. The agglomerated particle size estimated from SEM micrograph was 152±42 nm, which corresponded to the particle size distribution measured by a lazar scatter method. Furthermore, as for BaTiO₃ synthesis from Ba(OH)₂ and sub-micron sized TiO₂ powder, the rate constant of BaTiO₃ powder fabricated from assistance of ball milling process was increased (2.5×10^-2), as compared to a conventional hydrothermal reaction.

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A previously proposed method for depositing Ag nanoparticles on silica particles was extended to the preparation of ZnO-supported Pd (Pd/ZnO) catalysts. The method presented in this work consists of two steps: (1) Sn²⁺ ions are adsorbed on the surfaces of ZnO particles, and (2) Pd²⁺ ions added are reduced by oxidization of Sn²⁺ to Sn⁴⁺ and simultaneously adsorbed on the surface. TEM observations revealed that Pd nanoparticles with an average size of 2-3 nm were formed on the 20 nm ZnO particles. The Pd nanoparticles were transformed into a Pd-Zn alloy by partial oxidation and steam reforming of methanol, and consequently the Pd/ZnO attained CH₃OH conversion efficiencies of 35-50% at reaction temperatures of 310-370°C.

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Highly c-axis-oriented aluminum nitride (AlN) thin films were prepared on Inconel substrates using the RF magnetron sputtering technique. The AlN film characteristics were evaluated under pressures of 10.0 to 300.0 MPa and frequencies of 0.1 to 30 Hz at room temperature. The deviation from the linearity of charges with pressures for the AlN films were within 0.58% of a full scale at 300.0 MPa, which indicated a good linearity between 10.0 and 300.0 MPa. Furthermore the time dependence of charge for the AlN films hardly changed under pressure of ±0.8 MPa at 450°C in the time range from 0 to 54 h, which indicated a good durability. It is confirmed that the AlN thin films showed good potential as a pressure sensor under high temperatures and high pressures.

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Organic-inorganic hybrid low-melting glasses with extremely low water-absorption were obtained by the complete removal of OH groups which are hydrophilic substituents from phenyl-modified siloxane glasses by heat-treatment. The saturated water-absorption was estimated to be below 0.1 mass%. The thickness, bulk density and refractive index of such glasses remained unchanged even after soaking in water at 23°C for 192 h.

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