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Titanium dioxide nanocrystalline particles were synthesized by peroxo titanium acid (PTA) approach from titanium alkoxide and inorganic salt precursors, and their structural and surface properties, porosities, and photocatalytic activities were comparatively examined by XRD, TG/DTA, DRIFT, UV-vis, low temperature N-2 adsorption, and methyl orange (MO) degradation. It was found that nanoparticles with single anatase phase can be obtained from alkoxide precursor even near room temperature if synthesis conditions are appropriately controlled. PTA-derived anatase nanoparticles from titanium alkoxide precursor have smaller crystalline sizes and better porosities, and contain less amount of peroxo group and no organic impurities as compared to those from TiCl4 precursor. The advantages in structural property, porosity, and surface properties (few deficiencies) lead to a much better photocatalytic activity for TiO2 nanoparticles from titanium alkoxide precursor in comparison with those from TiCl4 precursor. (C) 2008 Elsevier Inc. All rights reserved.

It is well known that eutectic system forms characteristic structures in which different phases are entangled each other. Generally, such eutectic structures are formed by cooling a melt of eutectic composition of the components. These structures generally have submicron scale. We developed a new method to form very fine microstructures having one order or two orders smaller structures compared with the ordinary methods in Gd2O 3-Al2O3 and Y2O3-Al 2O3 systems. In our method, such structure was obtained by crystallization from amorphous. The reason of such ultra fine structure is attributed to a suppression of convection in the mother phases during the crystallization. Materials formed by this method are film or flakes. For the actual use, it should be consolidated. Well sintered body having ultra fine eutectic structure was successfully obtained using SPS method.

A mixture Of Y2O3 and Al2O3 with a eutectic composition was melted and quenched rapidly to form an amorphous phase. A eutectic microstructure, which was formed from the amorphous phase, was investigated. A heat-treatment of the amorphous phase at 1000 degrees C and 1300 degrees C for 30 min formed an Y3Al5O12 (YAG: Yttrium Aluminium Garnet)-Al2O3 eutectic microstructure. The eutectic microstructure, which was formed from the amorphous phase at 1300 degrees C for 30 min, was ultra fine. The amorphous film was pulverized and sintered both by conventional sintering and Spark Plasma Sintering (SPS). Following conventional sintering the eutectic microstructures of the conventionally sintered specimens became coarse. By using the conventional sintering method, a high sintering temperature (1600 degrees C) and long sintering time (24 h) was required to form dense specimens. This resulted in grain growth. On the contrary, the SPS sintered body had an ultra fine eutectic microstructure with a high bulk density. SPS was successful in suppressing grain growth. (c) 2007 Elsevier Ltd. All rights reserved.

Homogeneous-eutectic microstructure of Y(3)Al(5)O(12)-Al(2)O(3) system without coarse primary crystals was formed at an off-eutectic composition. This method utilizes a low migration rate in an amorphous phase. A mixture Of Y(2)O(3) and Al(2)O(3) having the off-eutectic composition was melted and quenched rapidly to form an amorphous phase. A heat-treatment of the amorphous phase at 1000 degrees C and 1300 degrees C for 30 min formed Y(3)Al(5)O(12) and Al(2)O(3) phases. SEM observation of this material, which was formed from the amorphous phase at 1300 degrees C for 30 min, showed homogeneous eutectic-like microstructure. The formation of the primary crystals (coarse Al(2)O(3)), which are always observed in the off-eutectic compositions by ordinary method, was completely suppressed. (c) 2008 Elsevier Ltd. All rights reserved.

The titania particles were prepared by aging the mixture of titanium isopropoxide (TIP) and H2O at 318 K. The anatase titania particles were obtained by the aging procedure at 318 K for more than 16 It. The aging temperature was quite low to obtain anatase-type titania particles. According to the DTA measurement, the amount of amorphous phase included in the titania particles decreased with increases in the aging time. Furthermore, the titania particles obtained by aging the mixture of TIP and H2O at 318 K for 24 h contained no amorphous phase. The obtained titania particles had a high BET specific surface area of more than 250 m(2)/g. To characterize the titania surface, the adsorption isotherms of the organic dye molecules in an aqueous solution were measured. The negatively charged Evans blue molecules strongly adsorbed on the titania surface obtained by the low-temperature hydrolysis reaction as compared with the results of the methylene blue molecules. Furthermore, the decomposition kinetics of the dye molecules by the photocatalytic activity also deepened with the charge of the dye molecules. The relation between the UV irradiation time and the molar ratio of the decomposed dye molecules followed the Avrami equation. According to the results of the analysis using the Avrami equation, the Evans blue molecules were decomposed on the titania particle surface. In contrast, the methylene blue molecules were decomposed in the aqueous solution. The difference in kinetics was related to the interaction of the dye molecules and the titania surface. The high surface area of the titania particles obtained the low-temperature hydrolysis reaction of titanium alkoxides enhanced the effect of the surface interaction on kinetics of the photocatalytic activity.

BaTiO3 particles were prepared by heating a suspension of titania derived from the hydrolysis of titanium isopropoxide in a barium hydroxide [Ba(OH)(2)] aqueous solution. Well-crystal lized cubic phase BaTiO3 fine particles were obtained by heating at a temperature >328 K for 24 h. The morphology and size of the obtained particles were affected by the reaction temperature and the Ba(OH)(2)/titanium alkoxide molar ratio. The secondary particles with a larger size were obtained at a lower reaction temperature. The nucleation process of BaTiO3 depended on the reaction temperature. The formation mechanism of BaTiO, and the formation kinetics were investigated by measuring the concentrations of Ba2+ ions in the solution during the heating process. The BaTiO3 particle formation occurred on the surface of the titania particles after strong adsorption of the Ba2+ ions from the solution. The experimental results showed that the heterogeneous nucleation of BaTiO3 occurred on the titania surface.

A controlled procedure leads to formation of pure anatase nanoparticles from titanium alkoxide near room temperature, without using any organic solvent by the peroxotitanic acid approach. The nanoparticles are highly mesoporous, with the surface covered by peroxo groups, and have excellent photode-composition activity as compared to those prepared from ordinary procedures.

Boride ceramics are useful materials because of their high strengths, hardness and melting points, which allow them to be used as high-temperature structural materials. In this study, sintered bodies of a solid solution of ZrB2-TiB2 system were prepared using hot pressing (HP) and spark plasma sintering (SPS). The sintering behavior was evaluated, and the effect of pulverization on sinterability and reactivity was examined using a Nanomizer. The combination of SPS processing at 2200 degrees C and pulverization yielded a nearly single-phase Zr0.5Ti0.5B2 solid solution having a relative density of 95%. (C) 2006 Elsevier Ltd. All rights reserved.

Zinc oxide (ZnO) nanoparticles were obtained by heating Zn(OH)(2) in a diol solution. When ethylene glycol, 1,3-propanediol and 1,4-butanediol were used for the heat treatment of Zn(OH)(2), ZnO nanoparticles can be obtained by heating at more than 308 K. In particular, when ethylene glycol was used for the heat treatment of Zn(OH)(2), the stable sols with the dispersion of the ZnO nanoparticles whose average diameter was less than 20 nm were obtained. Furthermore, when the heating temperature was 308 K, the spherical secondary particles with ZnO primary nanoparticles were obtained. The porosity in the secondary particles can be controlled by the diol solution used for heating of Zn(OH)(2). (c) 2006 Published by Elsevier B.V.

Porous materials were prepared by stacking needle-like titania particles. The uniform, needle-like titania particles were synthesized by hydrothermal treatment of titanium hydroxide gel containing ethylenediamine. A seeding technique controlled the particle size of them. The obtained particles were dispersed in aqueous solutions with various pH values and vacuum-filtered to form bulk materials. Porous materials with uniform microstructure were obtained when the pH of the suspension was adjusted to the value suitable for generating electrostatic repulsion between dispersed titania particles. Changing the size of component particles also controlled the pore size of the porous titania.

Porous materials were prepared by stacking needle-like titania particles. The uniform, needle-like titania particles were synthesized by hydrothermal treatment of titanium hydroxide gel containing ethylenediamine. A seeding technique controlled the particle size of them. The obtained particles were dispersed in aqueous solutions with various pH values and vacuum-filtered to form bulk materials. Porous materials with uniform microstructure were obtained when the pH of the suspension was adjusted to the value suitable for generating electrostatic repulsion between dispersed titania particles. Changing the size of component particles also controlled the pore size of the porous titania.

A thin film of Bi₄Ti₃O₁₂ was prepared from a layered assembly by alternative spin-coating of a sol-gel solution and a Bi₄Ti₃O₁₂ seed suspension on a glass substrate. The layered assembly was heated at various temperatures and the crystallization behavior was studied. For comparison the thin film of Bi₄Ti₃O₁₂ was also prepared from a spin-coated sol-gel solution without the seed crystal. In case of the layered assembly with seed crystal Bi₄Ti₃O₁₂ was crystallized at 450°C, while without the seed crystal Bi₄Ti₃O₁₂ was not crystallized at the same temperature. Without the seed crystal, higher temperature was required for the crystallization and pyrochlore phase was also observed. Higher temperature led a reaction between the spin-coated layer and the glass substrate, causing a deterioration of the substrates. Formation of thin film of Bi₄Ti₃O₁₂ crystal at temperatures below 450°C is required for the LSI fabrication, and the process developed in this study meets such requirements.

A method to estimate compositional fluctuation in (Ti<SUB>1-<I>x</I></SUB>, Zr<SUB><I>x</I></SUB>) B<SUB>2</SUB> system using a value of the width of the fluctuation of lattice spacing was developed. This system forms a complete solid solution. All the compositions have hexagonal symmetry. The fluctuations of lattice spacings of (<I>hk</I>·0) planes and (00·<I>l</I>) planes have different values, because the dependencies of a-spacing and c-spacing on the composition are different. The compositional fluctuation was determined from the measured values of the fluctuation of the lattice spacings. Effect of the mechanical strain on the determination of the compositional fluctuation was examined, because the mechanical strain also affects the measured values of the fluctuation of lattice spacings. The examination showed that the mechanical strain can be neglected in this measurement. Relation between measured compositional fluctuation and composition showed that (Ti<SUB>0.5</SUB>Zr<SUB>0.5</SUB>) O<SUB>3</SUB> had largest compositional fluctuation for samples prepared under the same conditions. (Ti<SUB>1-<I>x</I></SUB>, Zr<SUB><I>x</I></SUB>) B<SUB>2</SUB> by spark plasma sintering had smaller compositional fluctuation compared with those by hot press sintering.

Complexes between TiO2 and sugar alcohol molecules or polyol molecules were prepared by heating the mixture of titanium isopropoxide (TIP) and ethylene glycol, glycerin, meso-erythritol, or D-mannitol aqueous solution at 368 K for 24 h. The degree of crystallization of TiO2 in the obtained TiO2-sugar alcohol or polyol complex depended on the concentration of the polyol and sugar alcohol aqueous solution. When the TiO2-sugar alcohol or polyol complex was prepared by using the same concentration of the sugar alcohol or polyol aqueous solution, the degree of crystallization of the TiO2 in the complex decreased with increase in the number of OH groups per molecule. According to the results of the DTA measurements and the element analysis, the strength of the interaction between Ti4+ ions and polyol or sugar alcohol molecules increased with increases in the number of OH groups in the molecules. The heat treatment of TiO2-D-mannitol complex in 0.5 mol/l HNO3 aqueous solution at more than 318 K enabled to obtain TiO2-D-mannitol complex nanoparticles by breaking the bonds between the D-mannitol molecules and Ti4+ ions. The obtained TiO2-D-mannitol complex nanoparticles had large surface area which was more than 300 m(2)/g and showed photocatalytic activity. Furthermore, the complex nanoparticles can be dispersed into the distilled water with high stability.

Rod-shaped sintered body of a composition, 0.25La2O 3-0.75SiO2, was melted and rapid quenched. It formed an amorphous film. It was ground and sintered both by the normal sintering method and by the spark plasma sintering technique. By the normal sintering method, it crystallized before it was densified. By the spark plasma sintering technique the amorphous powder was densified before it crystallized. Optimum condition for obtaining well sintered material without crystallization was 850°C without soaking.

本研究では、水熱法を用いて粒径が均一で、かつ針状に形状異方性を有するチタニアおよびアルミナ系粒子を合成し、得られた粒子を用いての多孔体作製を試みた。この際、様々な粒径の粒子を調製することにより、孔径の制御も試みた。得られた粒子を、それぞれpHを調製した分散媒に分散し、吸引濾過によりバルク状の多孔体としての成形を試みたところ、粒子間に反発力が生じやすいような条件の分散媒を用いた場合に、割れやひびの生じにくい多孔体を作製することが出来た。用いる粒子の粒径を変えた場合も均一な多孔体を成形することが可能であり、得られた多孔体は、粒子の粒径に依存した孔径を有していた。

本研究では、針状に形状異方性を有するチタニア粒子の積層によるセラミックス多孔体の作製を試みた。まず、水酸化チタンをアミン類等の吸着物質存在下で水熱処理することにより、粒径が均一で、かつ針状に形状異方性を有するチタニア粒子を合成した。また、酸性条件下での水熱合成により調製した、非常に微細なチタニアナノ粒子を種結晶として用いることにより、針状チタニア粒子の粒径を変化させてそれぞれ合成した。得られた粒子を水中に分散、吸引濾過を用いて成形することにより、多孔体の作製を行った。均一な粒径を有する異方性粒子を用いたことにより、得られる多孔体は気孔率が大きく均一な細孔径を有していた。

ZrB2とTiB2の固溶体は単体よりも機械的特性が向上することが報告されている。しかし、これらの物質は緻密な焼結体を得ることが難しい材料として認識されている。本研究では、低温短時間で緻密な焼結体を得ることができる放電プラズマ焼結(SPS)法を用いてZrxTi1-xB2固溶体セラミックスの作製・評価を行い従来法であるホットプレス(HP)法と比較した。SPS法を用いることで、HP法より焼結温度が300℃も低く保持時間も1/12程度で、HP法と同程度の相対密度・ビッカース硬度・電気伝導度をもつ焼結体を得ることができた。また、SPS法による低温・短時間での焼結により組成変動幅の小さな固溶体を得ることが出来た。

Sintering of a mixture of different compositions generally causes a change. in the compositional distribution in the starting material. Change in the compositional distribution during sintering was examined for normal sintering, hot pressing and spark plasma sintering (SPS). Only SPS method produced a highly sintered material without changing the initial compositional distribution. Combination of pyroelectric properties of different compositions was accomplished by SPS. A mixture of three compositions corresponding to pyroelectric materials having the peak at 0 degrees C, 25 degrees C and 50 degrees C were mixed and sintered by the normal sintering method. The normal sintering resulted in a pyroelectric material having single peak, due to the homogenization process during the sintering. Sintered material by SPS produced a material having pyroelectric peaks corresponding to the initial compositions. Combination of SPS and diffusion-treatment produced a pyroelectric materials having high pyroelectric coefficient in the temperature range between 25 degrees C and 50 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.

Complexes between TiO<sub>2</sub> and sugar alcohol molecules or polyol molecules were prepared by heating the mixture of titanium isopropoxide (TIP) and ethylene glycol, glycerin, meso-erythritol, or D-mannitol aqueous solution at 368 K for 24 h. The degree of crystallization of TiO<sub>2</sub> in the obtained TiO<sub>2</sub>-sugar alcohol or polyol complex depended on the concentration of the polyol and sugar alcohol aqueous solution. When the TiO<sub>2</sub>-sugar alcohol or polyol complex was prepared by using the same concentration of the sugar alcohol or polyol aqueous solution, the degree of crystallization of the TiO<sub>2</sub> in the complex decreased with increase in the number of OH groups per molecule. According to the results of the DTA measurements and the element analysis, the strength of the interaction between Ti<sup>4+</sup> ions and polyol or sugar alcohol molecules increased with increases in the number of OH groups in the molecules. The heat treatment of TiO<sub>2</sub>-D-mannitol complex in 0.5 mol/l HNO<sub>3</sub> aqueous solution at more than 318 K enabled to obtain TiO<sub>2</sub>-D-mannitol complex nanoparticles by breaking the bonds between the D-mannitol molecules and Ti<sup>4+</sup> ions. The obtained TiO<sub>2</sub>-D-mannitol complex nanoparticles had large surface area which was more than 300 m<sup>2</sup>/g and showed photocatalytic activity. Furthermore, the complex nanoparticles can be dispersed into the distilled water with high stability.<br>

Transparent lanthanum-doped lead zirconate titanate (PLZT) ceramics with high density were fabricated using spark plasma sintering (SPS), a recently developed hot-pressing method. A wet-dry combination method was used to prepare the fine PLZT powders. The average grain size of the PLZT ceramics was less than 1 mu m, because of a relatively low sintering temperature and a very short sintering time. The transmittance of PLZT ceramics increased with an increase of calcination temperature up to 700 degrees C and then it slightly decreased with further increase of calcination temperature. The transmittance strongly depended on the SPS temperature and heat-treatment temperature. The pellet sintered at 900 degrees C for 10 min and heat treated at 800 degrees C for 1 h with a thickness of 0.5 mm showed a transmittance of 31% at a wavelength of 700 nm. The relationships between the transmittance and the microstructure were investigated.

A new method for bonding blocks of Si3N4 has been developed that produces bonds whose maximum service temperature is equal to the temperature used during the bonding process. In the present paper a system consisting of blocks of Si3N4 coated with a preceramic film containing a fine dispersion of silicon and a thin layer of germanium powder has been investigated to determine the effect of the thickness of the germanium film. The maximum service temperature is not determined by the melting point of the germanium since the germanium forms a higher melting point solid solution with the silicon in the film. Control of the thickness of the germanium film is found to be critical as a thicker layers results in lower strength bonds owing to differences in thermal expansion, and the maximum service temperature is lower owing to the lower liquidus temperature of the leaner Ge-Si solid solution. This technique has potential applications in fuel cells as a result of the small differences in thermal expansion coefficients and firing shrinkage in fuel cell materials, thus allowing successful fabrication and joining of monolithic solid oxide fuel cells (MSOFCs) with few defects.

チタンの水酸化物ゲルを水熱処理することにより、粒径、形状が均一なチタニア粒子を合成した。その際に形態制御剤としてエチレンジアミンを添加することで、粒子の形態を針状に制御することが出来た。さらに、微細なチタニア種結晶粒子を系内に添加することにより、長軸径を数十から数百ナノメートルの間で連続的に制御して、均一な針状粒子を作製出来た。また、この針状粒子においては、(100), (110)面が優先的に成長していることも確認された。メチレンブルーの光分解試験においても、針状粒子を用いた場合、等方的な粒子に比べて高い光分解活性が確認されたため、(100), (110)面が他の面と比較して良好な光触媒特性を有している可能性が示唆された。

水熱条件下でのチタン酸ビスマス粒子合成時における、チタン源と鉱化剤の影響を詳細に調べた。チタン源としては、アルカリ水溶液中に直接チタンアルコキシドを投入して得た水酸化チタン、アルコキシド法により合成した水和チタニア、水和チタニアを仮焼して得られるアナターゼ型に結晶化したチタニア粒子をそれぞれ用いた。その結果、チタン源の反応性および硬化剤の種類、濃度が生成する粒子の形状、結晶相に大きく影響することが判明した。水和チタニアを原料に用いた場合には、比較的高温で水熱処理を行うことによって、平均粒径が数十ナノメートルオーダーのBi₄Ti₃O₁₂粒子を得ることが出来た。

Lead titanate (PbTiO3) is difficult to sinter without additives, even when a spark-plasma-sintering technique is applied. The high tetragonality, c/a, of PbTiO3 causes destructive strain after sintering. We found that a sintered body of PbTiO3 could be obtained, when the PbO/TiO2 value was <0.9. However, decreasing the ratio did not increase the bulk density; rather, it caused a decrease in the grain size. The mechanical strain that resulted from the phase change from cubic, at the sintering temperature, to tetragonal, at room temperature after the sintering, was released by the decrease in the grain size.

A mixture of Al2O3 and GdAlO3 was melted and rapid quenched to produce an amorphous film. Dense eutectic composites were consolidated from ground amorphous powder using both conventional and spark plasma sintering (SPS). Conventional sintering at temperatures above 1600degreesC for 24 h was required for complete sintering. However, using SPS complete sintering could be obtained at temperatures between 1300 and 1500degreesC with no soaking. The SPS technique could consolidate ultrafine eutectic structure from rapid quenched amorphous material, whilst conventional sintering was not successful owing to grain growth. A combination of rapid quenching and SPS resulted in an ultrafine eutectic Al2O3-GdAlO3 structure.

Spark plasma sintering (SPS) combined with heat treatment was investigated to prepare laminated ceramics from compositions having quite different sintering temperatures. Although the optimal sintering temperature of BaNd2Ti4O12 (BNT) ceramics was much higher than that of Bi4Ti3O12 (BIT) ceramics, sandwiched BaNd2Ti4O12/Bi4Ti3O12/BaNd2Ti4O12 (BNT/BIT/BNT) composite ceramics were successfully prepared with this new method. The results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the BNT layers and the BIT layer were well bonded and no significant diffusion between them was observed. The temperature coefficient of dielectric constant of the laminated ceramic was found to be much smaller than that of BNT ceramic. (C) 2003 Elsevier Science B.V. All rights reserved.

As an application of characteristic of spark plasma sintering (SPS) method, which can produce highly sintered material with almost no change in compositional distribution, sintered materials that consist of different compositions were prepared. Perovskite three component system, xPb(Zn1/3Nb2/3)O-3-yPbZrO(3)-(1-x-y)PbTiO3, exhibits a very sharp pyroelectric peak at phase transition temperature between F-RL and F-RH phases. When a mixture of calcined materials having different compositions of this system was sintered by SPS, the compositional distribution in the starting mixture was almost maintained. The sintered material exhibited high pyroelectric coefficient over a wide temperature range. (C) 2002 Elsevier Science B.V. All rights reserved.

The sintering characteristics and the change in the compositional distribution in the PbTiO3PbZrO3-Pb(Mg1/3Nb2/3)O-3 system during the sintering process by spark plasma sintering (SPS) method were-examined. They were compared with those by a normal sintering method. The densification by the normal sintering was slow even at high temperatures. When SPS method was employed, much lower temperature and shorter period resulted in sintered bodies having almost the theoretical density. As expected in normal sintering, the compositional distribution decreased as the sintered density increased. On the contrary, the change in the compositional distribution by SPS was much smaller than that in the normal sintering. This sintering characteristic of SPS suggested a possibility of fabrication of sintered material having a desired compositional distribution.

Laminated ceramics have received widely scientific and commercial attention because their properties, such as mechanical properties and electrical properties, can be tailored by adjusting the structure, thickness and composition of the different layers. For example, ferroelectric Bi4Ti3O12 (BIT) which has a positive temperature coefficient of dielectric constant (T.) can be used to modify the negative tau(epsilon) of typical microwave dielectric ceramic BaNd2Ti4O12 (BNT). However, BaNd2Ti4O12/Bi4Ti3O12/BaNd2Ti4O12 (BNT/BIT/BNT) laminated ceramics could not be prepared by the general method because the optimal sintering temperature of BaNd2Ti4O12 ceramic (around 1350degreesC) was much higher than that of Bi4Ti3O12 ceramic (around 1100degreesC). In this research, a new method of spark plasma sintering (SPS) combined with post-sintering was successfully proposed to prepare BNT/BIT/BNT laminated ceramics. It was divided into three steps. In first step, the BaNd2Ti4O12 ceramics were prepared by conventional sintering method. In second step, the calcined and pre-pressed Bi4Ti3O12 powders were sandwiched between BaNd2Ti4O12 ceramic pellets and spark plasma sintered at 900degreesC for 10min to synthesize BNT/BIT/BNT composite ceramics. In the last step, a post-sintering was employed to reoxidize the partially reduced BNT/BIT/BNT composite ceramics. The results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that BNT layer and BIT layer were well bonded and no significant interfacial infiltration between them was observed. The-sandwiched BNT/BIT/BNT ceramic with 10.7% BIT in volume has a dielectric constant of 92.8, a low dielectric loss of 0.0068 and a small temperature coefficient of dielectric constant of 35. ppm/degreesC at 1 MHz.

The microstructure, compositional fluctuation and dielectric properties of Pb(Zr0.3Ti0.7)O-3 ceramics prepared by spark plasma sintering (SPS) and heat treatment were investigated. The sample heat-treated for 1 h had a large compositional fluctuation, which decreased significantly with increasing heat treatment time up to 2 h and thereafter decreased slightly. It was found that the dielectric constant of above ceramics strongly depended on the compositional fluctuation. Specially, a linear relation between the peak width at two-third maximum dielectric constant of dielectric constant-temperature peak and the compositional fluctuation was observed. (C) 2002 Elsevier Science B.V All rights reserved.

The microstructures and pyroelectric properties of multicomposition 0.9PbZrO(3).xPbTiO(3).(0.1-x)Pb(Zn1/3Nb2/3)O-3 (PZPT-PZN) ceramics were investigated. The PZ-PT-PZN ceramics with nearly theoretical density were prepared by spark plasma sintering at low temperature (800degreesC) for a very short time (10 min) from two original compositions with x = 0.025 and x = 0.050. The heat treatment was successfully used to control the diffusion between the different compositions in such ceramics. For ceramics heat-treated at 900degreesC, two pyroelectric peaks corresponding to the original compositions were observed. When the heat-treatment temperature was increased to 1200degreesC, these two pyroelectric peaks combined into one sharp pyroelectric peak, which corresponds to average composition. When the spark-plasma-sintered ceramics were heat-treated at 950degreesC, a high and stable pyroelectric coefficient (>100 nC.cm(-2).K-1) over a wide temperature range (23degrees-47degreesC) was obtained. It was found that the pyroelectric properties strongly depended on the microstructures.

Sintered body of PbZrO₃-PbTiO₃-Pb (Zn_1/3Nb_2/3) O₃ system with high pyroelectric coefficient over a wide temperature range was obtained. Sintered body of a mixture of three compositions having pyroelectric peaks at different temperatures exhibited single pyroelectric peak. This was caused from the diffusion during the sintering. To avoid the effect of the diffusion, granules with different compositions were mixed, pressed into a powder compact and sintered. The compositional change by diffusion was suppressed by this method. This technique enabled the combination of different pyroelectric properties.

A new method of preparing transparent PbZrO3-PbTiO3-Pb(Zn1/3Nb2/3)O-3 (PZ-PT-PZN) ceramics was proposed. This is a multiprocess in which the mixtures of calcined powders were spark plasma sintered for 10 min and then thermally treated for 1 h. Although the sintering time was very short, the densities of the samples prepared by this method were nearly theoretical and the samples were optically transparent, The transparent PZ-PT-PZN ceramics could be promising candidates for applications to areas such as electrooptics and pyrooptics.

Pyroelectric properties of 0.9PbZrO(3-x)PbTiO3-(0.1-x)Pb(Zn(1/3)Nb(2/3))O(3) composite ceramics prepared with spark plasma sintering technique (SPS) combined with a thermal treatment were investigated. Dense composite ceramics were obtained from starting compositions of x = 0.025 and x = 0.05 by spark plasma sintering at 800degreesC for 10 minutes. Two pyroelectric peaks near 23degreesC and 47degreesC, which corresponded to two starting compositions, were observed for samples thermal treated at low temperatures. The diffusion between two compositions increases with increasing heat treatment temperature. Meanwhile, two pyroelectric peaks gradually transformed to one peak at 38degreesC, which corresponded to the average composition. When thermal treatment at 950degreesC for 1 h was employed, ceramics with gradient compositional distribution was obtained. This ceramic had high and stable pyroclectric coefficient in a wide temperature range.

La-doped lead magnesium niobate (Pb1-xLax[Mg(1+x)/3Nb(2-x)/3]O-3, PLMN, x= 0.1, 0.2) was prepared by a polyethylene glycol-based process (PEG method) as follows: PEG-cation (La3+, Mg2+, Nb5+) complex was oxidized and the obtained oxide was mixed with PbO. This oxide mixture was fired to obtain PLMN. This PEG method enabled to prepare the single phase of perovskite structure of PLMN at 1023 K, This temperature is lower than that used in the solid state reaction method. The PLMN prepared by the PEG method had quite little compositional fluctuation and structural strain. PLMN has an ordering domain with the super lattice structure of B site cations in the perovskite structure, The crystallite size of the ordering domain in the PLMN obtained by the PEG method increased when the molecular weight of the initial PEG increased (from 150 to 7500). The formation process of the ordering domain was under the influence of the cation distribution in the PEG-cation complex.

Multicomponent oxalate consisted of Fe3+ and M2- (M=Ni, Cu, CO, Zn) was prepared by heating the polyethylene glycol (PEG) solution of metal nitrate hydrate at 358 K for 3 h. The PEG-cation complex in the solution was oxidized by the nitrate ion so that the oxalate was obtained. The structure and the composition of the cations in the obtained oxalate depended on not only the composition of the PEG solution but also the molecular weight of PEG. The crystallinity and the particle size of the oxalate increased with an increase of the molecular weight of PEG. The relation between the cation composition in the PEG solution and that in the obtained oxalate also depended on the molecular weight of PEG. The two models that describe the formation process of the PEG-cation complex and the oxalate was examined. In the first model, it is assumed that the coordination of Fe3+ ions and that of M2+ occurs independently. In the second model, it is assumed that the coordination of Fe3+ and that of M2+ occurs cooperatively. The relation between the cation composition in the PEG solution and that of the obtained oxalate was derived from these models. According to the comparison between the experimental result and the consequences derived from the models, it is shown that the coordination of M2+ to PEG always occurs near the site where the coordination of Fe3+ occurred. The PEG-cation complex was formed under the cooperative process.

The adsorption isotherm and IR spectra of acetonitrile adsorbed on MCM-41 (pore-width = 3.2 mm) were measured at 303 K. The adsorption isotherm had a sharp jump at P/P-0 = 0.3 without adsorption hysteresis. The CN stretching nu(2)-band of adsorbed acetonitrile had two-component alpha- and beta-bands at 2263 and 2254 cm(-1), respectively, assigned to hydrogen-bonded molecules on surface hydroxyls of MCM-41 and physisorbed molecules in mesopores whose walls are coated with hydrogen-bonded molecules, respectively. The beta-band was analyzed with a time correlation function, giving a reorientation time tau. The tau value of the adsorbed molecule before capillary condensation was smaller than that of the bulk liquid, indicating a gas-like state. After capillary condensation, tau was the same as for the bulk liquid. (C) 1998 Elsevier Science B.V. All rights reserved.

The compositional homogeneity in the ceramic solid solutions is settled both by the process of the mixing of raw materials and by that of the diffusion during the firing. The mechanical mixing of raw materials is not effective against the homogenization below the grindable size. The homogenization process by the diffusion is not effective at large size. The gap where neither mechanical mixing nor diffusion is effective was considered to be the origin of the inhomogeneity in solid solutions. In order to verify this, a method to evaluate the region size of inhomogeneity was developed. Five areas having a certain size were randomly chosen on the EPMA image of a sample. Each area was divided into sixteen portions and the standard deviation of composition among these portions was estimated. This standard deviation can be considered as a degree of compositional inhomogeneity. The average standard deviation among the five areas was calculated. Such calculation was tarried out for various sizes. The average standard deviations were plotted against the size. Plots for models, in which the distribution of the composition forms a cheek pattern, exhibited peaks. The position of the peaks corresponded to the size of the check patterns. This method was applied to PZT samples prepared by the solid state reaction. The plots revealed the presence of the gap where neither mechanical mixing nor diffusion is effective.

Defective state of C-60 crystals was controlled by the recrystallization and annealing. The defective structure was examined by the X-ray diffraction and N-2 adsorption at 77 K. Recrystallized C-60 crystals without annealing showed broad diffraction peaks and the N-2 adsorption isotherm had marked low pressure uptake and a hysteresis in the high pressure region, indicating presence of both micropores and mesopores. The average micropore width was 8 Angstrom, which is closed to the C-60 molecular size, while the average mesopore one was 50 Angstrom. The mesopores disappeared by annealing up to 393 K. On the other hand micropores of 8 Angstrom remained even by heating up to 673 K.