Solid-state electrochemical sensors for volatile organic compounds (VOCs) based on commercial yttria stabilized zirconia (YSZ) sheet were fabricated using Pt or Pt covered with SmFeO₃ layers as electrodes. The sensing performances were strongly influenced by the surface morphology of YSZ. The overcoat with SmFeO₃ layer on the one side electrode enhanced the sensitivity for some VOCs. Even for 0.5 ppm of methyl ethyl ketone, ethanol and acetic acid, the changes of the electromotive force (EMF) in the levels of 20 mV and higher were confirmed at 400°C for the monolithic type sensor in which one side electrode was over-coated with SmFeO₃ powders.

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High-density SiC-AlN composites (50:50 in mol) were fabricated from powder mixtures of SiC and AlN by SPS process in the temperature range of 1800-2100°C. Relative densities of the composites increased with increasing firing temperature. It revealed that the mixed phases of 3C and 2H formed at 1800°C, 1900°C and 2000°C, and only 2H phase formed at 2050°C and 2100°C. The sintering of SiC and AlN particles proceeded hardly at 1800°C. The densely sintered SiC-AlN composites were obtained above 1900°C. At 1900°C and 2000°C, 3Css (β-SiC/AlN solid solution) and 2Hss (α-SiC/AlN solid solution) were found, in which Si-rich 2Hss and Al-rich 2Hss existed at 2000°C. Homogeneous SiC-AlN composites were obtained with grain-growth at 2100°C.

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Authors have been trying to fabricate cristobalite-containing mullite bodies with high strength and toughness by reheating mullite-glass sintered bodies. In this process, a phenomenon that once-crystallized cristobalite layer changed back to amorphous again was observed by the microstructure observation of the sample contaminated with Na₂O. In this study, the minimum amount of Na₂O to change the cristobalite phase into amorphous was quantitatively determined by the electron probe microanalysis (EPMA) method. As a result, the amount of Na₂O in the amorphous phase just near the cristobalite-amorphous phase boundary was 1.6-1.9 mass%, which almost corresponded with the minimum amount of Na₂O in the liquid phase coexisting with mullite, estimated from a phase diagram.

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Co-firing of a La_0.8Sr_0.2MnO_3-δ(LSM)-gadolinium doped ceria(GDC)/GDC/NiO-GDC cell is investigated by the application of a mixed GDC powder. A fine starting GDC powder is synthesized by the homogeneous precipitation process, using hexamethylenetetramine (HMT), and mixed with a commercially available GDC powder. Shrinkage behavior of the chemically prepared, the commercial, and the mixed GDC powders is examined by thermo-mechanical analysis (TMA), which suggests that the mixed powder has good sinterability and compatible shrinkage with electrodes. A LSM-GDC/GDC/NiO-GDC cell prepared by lamination of electrode and electrolyte green sheets is co-fired at 1300°C for 4h. The prepared fuel cell gives an output power density of 0.35 W/cm² at 600°C.

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Many lead-free materials, such as Bi-based compounds, BaTiO₃ or alkaline niobate compound, have been intensively studied. The microstructure and characteristics of BaTiO₃ ceramic are significantly influenced by addition of 4PbO-B₂O₃. Under low sintering temperatures, the grain growth of BaTiO₃ ceramic is enhanced by capillary action, rearrangement and solution-reprecipitation of the liquid phase. At high sintering temperatures, exaggerated grain growth of BaTiO₃ ceramic is restrained by the presence of a liquid phase. The glass frit also has significant effect on the dielectric and piezoelectric properties of BaTiO₃ ceramic. The measured density of BaTiO₃ ceramic with suitable addition of 4PbO-B₂O₃ glass frit and sintering temperature can get 95.7-98.8% dense. The peak value of the K^T₃₃ was 2500 with addition of 0.2 mol% glass frit at the sintering of 1250°C for 4 h. The maximum value of the k_p was 0.36 with addition of 0.2 mol% glass frit at the sintering of 1350°C for 4 h. With suitable amounts of glass frit and an optimized sintering temperature, the density is enhanced and the values of the dielectric and piezoelectric properties are improved.

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A series of Li₂O-La₂O₃-SiO₂ sinters were prepared with the various ratios of the associated elements, Li: La: Si = x: (10-x): 6, and their ionic conductivities were examined. All the sinters were mainly composed of the apatite-type Li_xLa_10-x(SiO₄)₆O_3-x crystalline phases but sub-phases were produced in some cases. The lattice parameters of the main phase decreased with an increase in the Li-content, x, up to x = 2.0 and became constant above x = 2.0, indicating that La 4f-site was partially replaced by Li up to the maximum of x = 2.0. The conductivity of the sinters gradually increased with an increase in x to 1.5, but it suddenly dropped down at x = 2.0 and increased again by a further increase in x. The XRD and ²⁹Si-NMR results suggested that the first conductivity increase was due to the decrease in the content of the La₂SiO₅ sub-phase with the Li replacement. Furthermore, the ⁷Li-NMR measurements gave evidence that lithium silicate sub-phase was formed at above x = 2 in the grain-boundary of the crystalline phase as a high Li-ionic conducting phase. The Nernst's EMF response of the O₂ and CO₂ concentration cells suggested that the main ionic carriers were oxide ion at x < 2.0 and lithium ion at x ≥ 2.

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The aim of present study is to investigate the effect of preforms on the synthesis of micro β-SiC. For this purpose, preforms were prepared from commercially available phenol resin and silicon powders by pyrolysing at 650°C and 750°C in vacuum. Then, preforms were hot isostatically pressed (HIPed) at 1400°C for 10 min in an argon atmosphere of 50 MPa to synthesize micro β-SiC. X-ray diffraction analyses showed that the formation of β-SiC was enhanced in the specimens prepared by HIPing the preforms pyrolyzed at 750°C, which might be due the more carbonization and the development of porous structure in the range 600-800°C. Scanning electron microscopy observations revealed the formation of micro-crystals (up to 8 μm in size) with facets in the HIPed specimens. In addition, the degree of crystallites in the specimen obtained from the preforms pyrolyzed at 750°C was higher than the preforms pyrolyzed at 650°C. The energy dispersive spectroscopy showed that crystals were of SiC because the atomic ratio of silicon and carbon atoms in the crystals was almost 1 : 1. The density of the specimens obtained by HIPing the preforms pyrolyzed at 750°C was (3.11 g/cm³) more than the specimens obtained by HIPing preforms pyrolyzed at 650°C (2.95 g/cm³). The HIPing process, in addition to densification, led to the formation and growth of β-SiC.

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An effective approach for preparing electrically conductive SiAlON-TiN composites have been developed. Granules of a designed composition of α-β SiAlON were obtained by spray drying and coated with varying amounts of TiO₂ powder (0-10 vol%) homogenously by mechanical mixing. Fully dense composites were obtained by spark plasma sintering (SPS) under a pressure of 50 MPa at 1650°C for 5min. According to the scanning electron microscope (SEM) analysis, unique microstructures containing continuously segregated in-situ formed TiN phase in 3D were achieved. Additionally, X-ray diffraction (XRD) studies revealed that all TiO₂ was successfully converted to TiN. The resistivity of the α-β SiAlON (1 × 10¹¹ Ω·m) was drastically reduced down to 2 × 10^-4 Ω·m at 5 vol% TiO₂ addition.

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Hydroxyapatite (HA) whiskers were synthesized by a hydrothermal method and ion conductive property was investigated in order to develop HA whisker electrets for biomedical utilization. Based on infrared (IR) spectroscopy and inductively coupled plasma optical emission spectrometry (ICP-OES), the obtained whiskers were assumed to be Ca deficient HA with a composition of Ca_9.18[HPO₄]_0.82[PO₄]_5.18[OH]_1.18·n H₂O. The results of complex impedance measurements proved that the conduction properties of whiskers and powders showed almost the same temperature dependence as those of sintered HA above 600°C. The mechanism is understood by the migration of protons originating in OH^- ions. In the temperature range below 600°C, however, the non-linear Arrhenius relationship of conductivity (σ vs. 1/T) was only observed in the whiskers and powders. In particular, a drastic change in conductivity with temperature appeared in the whiskers within 250-600°C; the conductivity increased to 5.0 × 10^-9 S/cm at 500°C, then decreased to 1.7 × 10^-9 S/cm with the temperature elevated to 600°C. Since HPO₄^2- ions are reportedly supposed to convert into P₂O₇^4- in almost the same temperature range where the drastic change in conductivity appeared, the increase in whisker conductivity up to 500°C is presumably the result of an increase in the number of mobile protons generated from HPO₄^2-. The subsequent decrease in conductivity seemed to be caused by a decrease in the number of protons achieved by water elimination, causing the conversion of HPO₄^2- to P₂O₇^4-.

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Hot pressing (HP) at higher sintering temperature has been a traditional and prevalent technique for the fabrication of α-SiAlON. In order to prepare translucent SiAlON more easily, LiF was used as a non-oxide sintering additive to lower the sintering temperature to ≤ 1650°C. As a result, all of the samples possessed a good hardness and fracture toughness. At the same time, the lower temperature sintered samples showed a higher optical transmittance in the range of 2.5-5.5 μm wavelength (0.5 mm in thickness). The maximum infrared transmission reached 68% at a wavelength of 3.3 μm. The present work shows that the sintering process has a strong effect on microstructure and property of α-SiAlON. To be exact, a lower sintering temperature and longer holding time can produce some fully-developed microstrcture, which is beneficial for the optical transmittance.

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The influences of alkali oxides as glass constituents for producing LTCC (Low Temperature Co-fired Ceramics) materials were investigated in terms of variations in physical and dielectric parameters. The LTCC materials were based on typical calcium zinc aluminoborosilicate glasses containing 1-3.5 mol% alkali oxides such as K₂O, Na₂O and Li₂O. All samples were prepared in the same experimental condition, i.e., the ratio of glass/filler and the final firing temperature of 850°C. Densification and crystallization behavior strongly depended on the type and amount of alkali oxides used. For example, crystallization peaks in the DTA curves tended to shift towards the lower temperature region by increasing the content of Na₂O and K₂O. Specifically, the effect of Li₂O was distinct in determining the crystallization behavior and subsequent dielectric properties of the LTCC system. Dielectric constant was measured as values of 7.18-7.78 but dielectric loss was significantly degraded specifically with the addition of 3 mol% Li₂O.

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The effects of melting temperature and glass composition on the Near-infrared (NIR) luminescent characteristics of Te-containing borate glasses are investigated and compared with previous works. Three absorption bands are detected at around ~370 nm, ~430 nm and ~530 nm, however, the absorption band at around ~600 nm could not be detected in all borate glasses. And no NIR luminescence was observed under the excitation of a 974 nm laser diode. The NIR luminescence was observed in Te-green and Te-purple glasses, which showed the absorption band at around ~600 nm. This absorption band was ascribed to ²Πg → ²Πu transition of Te₂^-. Consequently, it is suggested that the origin of NIR luminescence of Te-containing green and purple glass is likely to be caused by Te₂^- center. (Not to sure of the meaning of this sentence...)

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Silica/poly(vinyl alcohol) organic-inorganic hybrid gas barrier layers on PP were prepared by the sol-gel method by microwave irradiation. The effects of microwave irradiation on the oxygen barrier property and surface hardness of the films were investigated. From IR measurement, no difference was observed in the spectra of the film prepared by microwave irradiation and by conventional heating. The oxygen barrier property of the film prepared by microwave irradiation was better than that of the film prepared by conventional heating. The results indicated that microwave irradiation was effective for synthesizing the organic-inorganic hybrid gas barrier layers in a short time. The hybrid barrier film obtained by microwave irradiation exhibits oxygen barrier properties.

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Aluminum oxide has been well known as the host matrix for the luminescent materials doped by luminescent centers such as Eu or Ce because of the low cost and the ease of forming. In this work, a fluorescent characteristic of the solid alumina was examined using low cost sol-gel technique. As a result, amorphous alumina sintered at 500°C generated visible luminescence at ~430 nm, and that sintered at 700°C showed visible luminescence at ~390 nm.

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Single crystals of BiFeO₃ were prepared by hydrothermal synthesis using hydrate sodium bismuth oxide (NaBiO₃·nH₂O) and iron nitrates (Fe(NO₃)₃·9H₂O) in the potassium hydroxide solutions. The size of BiFeO₃ single crystals increased with the reaction temperature and duration. Single crystals of sillenite-type Bi_12.5Fe_0.5O_19.5 and Bi₂Fe₄O₉ were also obtained depending on the conditions. From the chemical analysis, the chemical composition of the crystals was deduced to be Bi_0.96K_0.03FeO₃. Although the crystals contained a small amount of potassium, the lattice parameters of the crystals agreed well with the pure BiFeO₃ and the Curie temperature was not affected by this replacement.

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