Journal of the Ceramic Society of Japan
Online ISSN : 1348-6535
Print ISSN : 1882-0743
ISSN-L : 1348-6535
Volume 116, Issue 1360
(December)
Displaying 1-15 of 15 articles from this issue
Special Article: The 62th CerSJ Awards for Academic Achievement in Ceramic Science and Technology: Review
  • Hiroshi FUNAKUBO
    2008 Volume 116 Issue 1360 Pages 1249-1254
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Degradation -free dielectric property was obtained by using films of bismuth layer-structured dielectrics (BLSDs) having a natural superlattice structure. Investigation of the effects of the stack direction of the bismuth oxide and pseudoperovskite layers on the dielectric properties of c-axis-oriented epitaxial BLSD films revealed that those with an even number of octahedra in the pseudoperovskite layer did not show significant degradation in the dielectric constant and retained good insulating characteristics when the film thickness was decreased despite the increased strain applied to the film. This was found not only in epitaxially grown films but also in one-axis-oriented ones with in-plane random orientation. In addition, films with a-/b-axis-oriented epitaxial BLSDs can be used a mold with a periodic nano-structure.
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Papers
  • Hiroyuki HIJIYA, Tetsuo KISHI, Atsuo YASUMORI
    2008 Volume 116 Issue 1360 Pages 1255-1259
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Glass ceramic phosphors containing fresnoite (Ba2TiSi2O8) were prepared from glasses both within and outside the immiscibility region of the BaO-TiO2-SiO2 system by conventional melt-quenching and subsequent heat treatment. The phosphors showed blue-white photoluminescence (PL) under ultraviolet excitation, and the effects of the crystalline phase precipitated and the fine structure of the ceramics on their PL properties were examined. Phase-separated textures were observed in the samples with compositions within the immiscibility region. The predominant crystalline phase precipitated in the heat-treated sample was fresnoite. Sample PL intensity was related not only to the amount of precipitated fresnoite, but also to the microstructure of the sample resulting from phase separation. The highest PL intensity was obtained from a 22BaO·11TiO2·67SiO2 sample from the immiscibility region, because of the formation of an appropriate fine glass-ceramic structure for photo-excitation of fresnoite.
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  • Sang-Kee LEE, Ikuko YAMADA, Shoichi KUME, Hiromi NAKANO, Kimihito HATO ...
    2008 Volume 116 Issue 1360 Pages 1260-1264
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    High-thermal-conductivity AlN ceramic with eliminated grain boundary phase was prepared by long-term sintering with Y2O3 addition at 1900°C for 100 h in a reducing N2 atmosphere. The thermal conductivity of polished surfaced of obtained ceramic was quantitatively measured at the micrometer-scale by using a thermoreflectance technique with periodic heating. This equipment measures the phase lag, which is the delay between the signal of periodic heating laser and the reflectance signal of detecting laser, to calculate thermal effusivity using the calibration curve obtained from standard materials. The conductivity of polished surface of the ceramic is calculated from obtained thermal effusivity, density and specific heat. The thermal conductivities on the densified and polished surface of the ceramic were ranged from 219 to 318 W/m·°C. Low-thermal-conductivity region (< 20 W/m·°C) relating to presence of hidden pores was observed in thermal conductivity map of the polished surface. Furthermore, high-resolution map of thermal conductivity demonstrated no significant reduction in thermal conductivities due to presence of grain boundaries.
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  • Tomoe SANADA, Masashi KAWAI, Hiroshi NAKASHITA, Taichi MATSUMOTO, Nori ...
    2008 Volume 116 Issue 1360 Pages 1265-1269
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Undoped and Tb3+-doped HfO2 spherical particles were prepared by a sol-gel method, by using hafnium tetra-t-butoxide (Hf(O-t-C4H9)4) as a precursor of hafnium dioxide, SPAN85® as a surfactant, mixed solvent of C2H5OH and n-C4H9OH, and H2O, followed by investigation of their structural and optical properties. Spherical particles with good morphology and comparatively high dispersibility were obtained from solutions with the molar ratio SPAN85®:H2O = 1:8-17.5, their sizes being 0.2-5 μm in diameter. Particles became small and aggregated when the molar ratio of H2O was more than 17.5, but became large when it was less than 8. Spherical particles heat treated at 400°C or below were amorphous, and those heat treated at 600°C or above were crystallized. Tb3+-doped HfO2 spherical particles showed green luminescence due to the 5D47FJ (J = 6, 5, 4, 3) transitions of the Tb3+ ion, and relatively strong luminescence was observed both in dried gel particles and particles heat treated at 1000°C. These Tb3+-doped HfO2 spherical particles can be expected for new optical materials.
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  • Hiroshi OHNISHI, Hironori NAKA, Tohru SEKINO, Yuichi IKUHARA, Koichi N ...
    2008 Volume 116 Issue 1360 Pages 1270-1277
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    The crystal phase and mechanical properties of 2.0 to 3.5 mol% Y2O3-stabilized zirconia polycrystals sintered from agitator milled powders (solid phase mixing, SPM) were investigated. Powders containing 2.5 and 2.8 mol% Y2O3 showed higher sinterability than those containing 2.0 and 3.5 mol% Y2O3. The thermal expansion curve of the 2.5 and 2.8 mol% Y2O3 samples exhibited a monoclinic to tetragonal phase transformation during the heating stage, with a linear relationship observed during cooling. However, a hysteresis was not observed during the heating and cooling stages when the Y2O3 content and sintering temperature were increased. The 2.0 mol% Y2O3 sample exhibited the transformation and hysteresis, even though the sintering temperature was increased. The relationship between the flexural strength and grain size for the sample with 2.0 mol% Y2O3 was not linear, but exhibited a peak. The flexural strength of the 2.5 and 2.8 mol% Y2O3 samples increased as the grain size increased, and then over a certain grain size the flexural strength remained constant and independent of the grain size. The flexural strength and fracture toughness of the 2.0 mol% Y2O3 sample might be dominated by microcrack-toughening. On the other hand, those for the 2.5 and 2.8 mol% Y2O3 samples were dependent not only on the stress-induced transformation, but also on the compressive residual stress and microcrack-toughening caused by the transformation. The relationship between the fracture toughness and Vfh, where Vf is the tetragonal phase fraction and h is the transformation depth, for the 2.0, 2.5 and 3.5 mol% Y2O3 samples was non-linear and exhibited a peak; however, that for the 2.8 mol% Y2O3 sample was linear.
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  • Tohru SUGAHARA, Michitaka OHTAKI, Takeshi SOUMA
    2008 Volume 116 Issue 1360 Pages 1278-1282
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Doping effects for the A-site in double-perovskite type oxide Sr2-xMxFeMoO6 (M = Ba, La) are investigated on the thermoelectric properties of the oxides. The Seebeck coefficient, S, shows that all the samples of both Ba- and La-doped Sr2FeMoO6 systems are n-type over the measured temperature range. In particular, the power factor, S2σ, of the Sr2FeMoO6 system largely increased with increasing Ba doping level up to x = 0.3. As a consequence, S2σ of Sr1.7Ba0.3FeMoO6 reached ca. 0.8 × 10-4 W/mK2, the largest value of all the samples in this study. The thermal conductivity, κ, shows a general trend in which the value decreases from ca. 1 W/mK at room temperature to ca. 0.7 W/mK at 1100 K. The dimensionless figure of merit, ZT, of the Ba-doped samples increased with increasing Ba doping level. Moreover, the ZT value drastically increased above 700 K due to the S2σ value increasing above 700 K and the κ value decreasing monotonically. As a result, the ZT value of Sr1.7Ba0.3FeMoO6 reached 0.31 at 1100 K.
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  • Takeshi OKUMURA, Yusuke MATSUKURA, Kimika GOTOU, Katsuyoshi OH-ISHI
    2008 Volume 116 Issue 1360 Pages 1283-1288
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Particle size dependence of CO2 absorption rate of powdered Li4SiO4 with four kinds of particle sizes was studied by SEM observation, particle size distribution measurement, and thermogravimetry. Average particle sizes of the powdered single phase Li4SiO4 samples were estimated about 26 μm, 34 μm, 53 μm, 70 μm, respectively by the particle size distribution measurement and SEM observation. The measurement of apparent rate constant k for the CO2 absorption reaction showed that k values of all the powdered Li4SiO4 samples increase with the increasing measurement temperature T, following the Arrhenius equation in the region of 620-660°C, while the k values abruptly increase deviating the Arrhenius equation over 670°C. It was also noted that the k values seem to depend on the particle size of the powdered Li4SiO4 samples, that is, the k values increase with the decreasing particle size. Moreover, difference between the k values of all the powdered samples at same temperature was found small in the region of 620-660°C, while the difference was found large over 670°C. For Li4SiO4 with smaller particle size, Δk = k700°C - k660°C was found larger, vice versa, the Δk was found smaller for Li4SiO4 with larger particle size. The values seem to correspond with reaction mechanism for CO2 absorption of Li4SiO4 particle.
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  • Jin Man HAN, Dae Soo JUNG, Jung Sang CHO, Yun Chan KANG
    2008 Volume 116 Issue 1360 Pages 1289-1294
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Spherical shape BaNd2Ti5O14 (BNT) powders were prepared by post-treatment of the precursor powders obtained by spray pyrolysis. The mean size and geometric standard deviation of the powders prepared at a low flow rate of the carrier gas as 5 Lmin-1 were 0.73 μm and 1.30. The powders post-treated at a temperature of 1000°C had a single phase of BNT without impurity peaks. The BNT powders had similar compositions to that of the spray solution. Necking between the powders occurred at a sintering temperature of 1100°C. The BNT powders with spherical shape changed to the rod-like crystals after sintering at temperatures above 1200°C. The aspect ratio of the rod-like crystals increased with increasing the sintering temperatures.
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  • Yoshitoyo NISHIO, Masakuni OZAWA
    2008 Volume 116 Issue 1360 Pages 1295-1298
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Lanthanum modified γ-alumina support that embedded highly dispersed LaAlO3 nano-particles in γ-alumina matrix were prepared by an impregnation process using aqueous lanthanum (III) nitrate. 5 mol% La added alumina was heated in the temperature range of 600-1200°C and characterized by surface area measurement, X-ray powder diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The added lanthanum should react with γ-Al2O3 to form LaAlO3 nano-particles in the secondary particle of alumina. LaAlO3 nano-particles with an average crystallite size of about 11 nm were found after heat treatment at 800°C, and the crystallite size of LaAlO3 nano-particles increased with the rise of heat treatment temperature.
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  • Ryo SAKAMAKI, Takuya HOSHINA, Hirofumi KAKEMOTO, Kouichi YASUDA, Hiroa ...
    2008 Volume 116 Issue 1360 Pages 1299-1303
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    A new heat radiation substrate for high power modules has been proposed by utilizing Al2O3 thick films formed by the aerosol deposition method (ADM) on Al substrates. Dense Al2O3 thick films (AD-Al2O3) could be obtained by the ADM at room temperature. A heat-cycle endurance test between -80°C and 180°C revealed that the AD-Al2O3/Al substrates were superior to the conventional direct brazed aluminum (DBA) substrates using AlN ceramics bounded to Al substrates. No lamination was observed between the AD-Al2O3 films and Al substrates after heat-cycle test in spite of the difference of thermal expansion coefficient between Al2O3 and Al. The in-plane thermal expansion coefficient of AD-Al2O3 films was almost the same as that of Al substrates, indicating that plastic deformation was induced in the AD-Al2O3 films consisting of nano-sized grains to relax the stress caused by the difference of thermal expansion coefficient.
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  • Keisuke ISHII, Shinjiro TASHIRO
    2008 Volume 116 Issue 1360 Pages 1304-1308
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    As a new technique to fabricate bismuth-layer-structured ferroelectric ceramics having a large size in the direction of c-axis orientation, the rolling-extended orientation method was developed. The green compacts having a large size in c-axis were easily obtained with lower lamination by piling up thicker uniaxially-oriented green sheets, which were fabricated by the rolling-extended orientation method. The rectangular bars having c-axis along their length direction were cut out of the green compacts. The relationships between the orientation degree and the fabrication conditions, such as the repetition number of the rolling-extended process, the size and the concentration of the templates in green sheets, were studied. The piezoelectric properties were compared between two rectangular samples having c-axis along their length direction and width direction.
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  • Makoto OGAWA, Takayuki MATSUTOMO, Tomohiko OKADA
    2008 Volume 116 Issue 1360 Pages 1309-1313
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Smectite like layered silicates with cation exchange capacity ranges from 60 to 90 mequivalent/100g clay were synthesized from LiF, Mg(OH)2 and colloidal silica. The controlled cation exchange capacity achieved by changing the composition of the starting mixture (namely the added LiF amount) successfully influenced the nanostructures of intercalation compounds prepared by the ion exchange with dioctadecyldimethylammonium ion.
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  • Tsuyoshi HONMA, Phan Thao NGUYEN, Takayuki KOMATSU
    2008 Volume 116 Issue 1360 Pages 1314-1318
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Crystal growth behaviors in CuO-doped Li2O-2SiO2 glasses by continuous-wave (cw) Ytterbium doped fiber laser (wavelength: 1080 nm) irradiations are examined. The lines (width: ~5 μm) consisting of highly oriented nonlinear optical lithium disilicate (Li2Si2O5) crystals are patterned in various laser powers (1.2-2.4 W) and scanning speeds (2-42 μm/s), and it is found that the crystal growth having the rates of 1 to 32 μm/s gives crystal lines with smooth surface morphologies. The critical (maximum) growth rates of Li2Si2O5 crystals in cw fiber laser irradiations are compared with the crystal growth kinetics (the reference data) in the Li2O-2SiO2 glass system determined by a conventional crystallization method in electric furnaces. It is proposed that the temperature of the fiber laser irradiated region for the Li2Si2O5 crystal growth would be 650-850°C. It is of importance to avoid crystal nucleation during laser irradiations for the patterning of homogeneous crystal lines.
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Express letters
  • Takeshi KUMAZAWA, Toru HONDA, You ZHOU, Hiroyuki MIYAZAKI, Hideki HYUG ...
    2008 Volume 116 Issue 1360 Pages 1319-1321
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Densification of boron carbide (B4C) was studied by pressureless sintering at temperatures ranging from 2108° to 2226°C with Al gas and Si compound gas derived from SiC. High purity boron carbide compacts attained a bulk density of a nearly full density (2.455 g/cm3) after being sintered at 2226°C.
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  • Manabu FUKUSHIMA, Masayuki NAKATA, Yu-ichi YOSHIZAWA
    2008 Volume 116 Issue 1360 Pages 1322-1325
    Published: 2008
    Released on J-STAGE: December 01, 2008
    JOURNAL FREE ACCESS
    Cordierite with ultra high porosity and oriented micrometer-sized cylindrical pores was prepared using a novel gelation-freezing method. Gelatin (used as the gelation agent), water (for formation of pores), and cordierite powder were mixed and cooled at 7°C. The obtained gel was frozen at -20 or -50°C, was dried using a freeze drier under vacuum, and then degreased at 600°C and sintered at 1200-1400°C for 2 h. The porosity was determined to be 93-79%, and was dependent on the powder content in the gel and the sintering temperature. SEM observations of the sintered body showed the microstructure of orderly uni-directionally oriented micrometer-sized cylindrical cells. The cell size was 25-235 μm, and these values were confirmed by the freezing temperature. The numbers of cells for the samples frozen at -20 and -50°C were 20-30 and 500-1500 cells/mm2, respectively, in the cross sections of the sintered bodies. The resulting porous cordierite with a total porosity of 87% showed a compressive strength of 4 MPa; this was thought to be due to the tight packing during freezing. The porosity, number of cells and strength were significantly higher than the reported values for other porous cordierite ceramics.
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