Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4236/msa.2015.64035

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We prepared nano-micrometer-architectural acidic silica from a natural amorphous iron oxide with structural silicon which is a product of the iron-oxidizing bacterium Leptothrix ochracea. The starting material was heat-treated at 500 C in a H2 gas flow leading to segregation of α-Fe crystalline particles and then dissolved in 1 M hydrochloric acid to remove the α-Fe particles, giving a gray-colored precipitate. It was determined to be amorphous silica containing some amount of iron (Si/Fe = ∼60). The amorphous silica maintains the nano-microstructure of the starting material - ∼1-μm-diameter micrometer-tubules consisting of inner globular and outer fibrillar structures several tens of nanometer in size - and has many large pores which are most probably formed as a result of segregation of the α-Fe particles on the micrometer-tubule wall. The smallest particle size of the amorphous silica is ∼10 nm, and it has a large surface area of 550 m2/g with micropores (0.7 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, we found that it has relatively strong Brønsted and Lewis acidic centers that do not desorb pyridine, even upon evacuation at 400 C. The acidity of this new silica material was confirmed through representative two catalytic reactions: ring-opening reaction and Friedel-Crafts-type reaction, both of which are known to require acid catalysts. © 2013 American Chemical Society.

DOI： 10.1021/am401029r

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

A chemical recycling process of inorganic wastes has been developed, where after vitrifying wastes, the glasses were heat-treated and soaked in an acid, obtaining colorless and transparent SiO2-abundant glasses. In the present study, distribution behavior of the constituents such as Si, P, Ti, Al and so on present in a municipal waste slag was examined. According to compositional analyses, the recovered solids after acid treatment consisted of SiO2, P2O5 and TiO2, suggesting the preferential distribution of P and Ti atoms into SiO2-rich phase during phase separation. In high resolution microscopic analyses, however, it was observed that P and Ti atoms were distributed separately from Si atoms, and they were present in the different particles insoluble in the acid. It was finally concluded that the insoluble solids were produced by a dissolution-reprecipitation process, that is, once all the constituents of the vitrified slag were dissolved in the acid, P2O5 and TiO2 coprecipitated as particles, and TiO2 was indispensable for the precipitation of P2O5. SiO2 also precipitated as particles separately from P- and Ti-containing particles. © 2013 The Ceramic Society of Japan and the Korean Ceramic Society.

DOI： 10.1016/j.jascer.2013.03.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

By heating an amorphous iron oxide produced by Leptothrix ochracea, an iron-oxidizing bacterium species, at 600-1100 degrees C in air for 2 h, vivid red-colored powdered materials including alpha-Fe2O3 (hematite) and amorphous silicate with high thermostability were prepared which offer potential for use as over-glaze enamels on porcelain. The precise color tone of the materials greatly depends on the heat-treatment temperature. The most strikingly beautiful sample, heat-treated at 800 degrees C, is light yellowish-red in color (L* = 47.3, a* = 34.1, and b* = 34.6), has a unique microstructure, and does not fade in color even with reheating at 800 degrees C, which is the firing temperature for over-glaze enamel on porcelain. The sample primarily consists of crystalline hematite particles similar to 40 nm in diameter with slightly longer axis unit-cell parameters than those of pure hematite. The particles are covered with amorphous silicate phase similar to 5 nm in thickness and are intricately interconnected into microtubules with an average diameter of 1.26 mu m. The attractive color of this material is due to the following structural features: small particle size (similar to 40 nm). nanocomposite of hematite and amorphous silicate, and a microtubule structure that inhibits aggregation of individual hematite particles and microtubules. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.dyepig.2012.06.024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In nature, there are various iron oxides produced by the water-habitant bacterial group called "iron-oxidizing bacteria". These iron oxides have been studied mainly from biological and geochemical perspectives. Today, attempts are made to use such iron oxides as novel functional materials in several applications. However, their quantitative structural characteristics are still unclear. We studied the structure of iron oxide of microtubular form consisting of amorphous nanoparticles formed by an iron-oxidizing bacterium, Leptothrix ochracea, using a combination of high-energy X-ray diffraction and reverse Monte Carlo simulation. We found that its structure consists of a framework of corner- and edge-sharing distorted FeO6 octahedral units, while SiO4 tetrahedral units are isolated in the framework. The results reveal the atomic arrangement of iron oxide of bacterial origin, which is essential for investigating its potential as a functional material. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2012.10.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Sodium borosilicate glasses containing phosphorus were prepared, and the effect of Al2O3 and TiO2 addition on the distribution behavior of phosphorus atoms associated with the phase separation was investigated. After heat treatment, a phase separation by the spinodal decomposition was commonly confirmed by SEM observation. In the additive-free sample, phosphorus was preferentially distributed into B2O3-rich phase after the phase separation, and after adding Al2O3 or TiO2, the amount of phosphorus distributed into SiO2-rich phase increased. It was also suggested that TiO2 had a stronger influence on the phosphorus distribution into SiO2-rich phase than Al2O3. P-31 MAS-NMR revealed that most of phosphorus atoms in the additive-free glass were present in PO4 units consisting of two terminal oxide ions, and the terminal oxide ions decreased and increased after the additions of Al2O3 and TiO2, respectively. It was suggested that this structural change brought about a change in the distribution of phosphorus. (C) 2012 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.120.490

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

SnO-P2O5 glasses have high refractive index and low glass transition temperature but have poor water durability. To improve water durability, NbO2.5 was added to SnO-P2O5 glasses, preparing SnO-NbO2.5-P2O5 glass. It was found that addition of only 4 mol % NbO2.5 was enough to achieve significant improvement of water durability, and at the same time, no degradation in thermal and optical properties was observed. (C)2012 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.120.530

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Surface crystallized glass-ceramics with nonlinear optical Bi2ZnB2O7 (BZB) crystals were prepared by ultrasonic surface treatment (UST) followed by crystallization heat treatment for stoichiometric glass with a composition of 33.3Bi(2)O(3)-33.3ZnO-33.3B(2)O(3). According to the surface XRD measurements and microscopic observations, UST technique was found to be quite effective for lower temperature precipitation of BZB, indicating the ability of crystallization control of the target phase, such as phase selectivity, small size of precipitates, high orientation and their morphology. After the optimization of the process condition parameters for improving transparency and suppressing deformation of the sample, the effective optical nonlinearity of the transparent surface crystallized glass-ceramics was estimated as 0.7 pm/V. (C)2012 The Ceramic Society of Japan. All sights reserved.

DOI： 10.2109/jcersj2.120.509

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Multiple regression analyses were applied to the prediction of glass structures, such as O 1s binding energy and fraction of fourfold coordinated boron atoms, N-4. In the case of linear combination of the content of glass constituents, an acceptable prediction accuracy was obtained for O 1s binding energy, and as for N-4, however, a poor agreement was observed between the prediction and measurement. After introducing quadratic and cubic interaction terms into the regression formula, a drastic improvement was achieved in the prediction of N-4. Some regression coefficients were dependent on basicity of each glass constituent, suggesting the feasibility of prediction for the glasses containing novel constituents whose regression parameters have never been determined. (C)2012 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.120.98

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：American Ceramic Society  

Transparent glass ceramics with highly oriented surface crystalline layers of fresnoite Ba2TiSi2O8 were prepared by heat treatment of precursor glasses in BaO-TiO2-SiO2 system. The orientation along c-axis of fresnoite crystals normal to the glass surface was evaluated by the surface XRD patterns, and it was remarkably enhanced by ultrasonic surface treatment (UST) before the crystallization using fresnoite powder suspension in water. The effect of UST disappeared after heat treatment in the glass transition region, and the mechanism of UST was discussed on the basis of the persistence at elevated temperatures.

DOI： 10.1002/9781118472590.ch18

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Basicity is defined as an electron donating ability of a material, and hence, an oxide material containing oxide ions with high electron density is regarded to be in high basicity. It has been demonstrated that basicity can be evaluated by binding energy of core level electrons, which is measured by X-ray photoelectron spectroscopy. Based on the experimental results obtained from a large number of oxide glasses, correlations among basicity, O1s binding energy, structure and properties of glasses have been investigated. In the present paper, some of the research outcomes are introduced. (C)2011 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.119.720

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Language：Japanese  

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J-GLOBAL

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Various non-oxides, such as SiC, Si3N4 and AlN were added to MgO-Al2O3 refractory, and the effect on the slag corrosion resistance was investigated. The specimens were prepared by a spark plasma sintering (SPS) method. Slag corrosion tests were carried out using a button method under a reducing atmosphere. Improvement in corrosion resistance was confirmed for the SiC-added specimens, and the addition of nitrides, however, resulted in deterioration. Wettability was also examined, and the compositional dependence was not observed in contact angle. Quantitative relation was not found between contact angle and penetration depth.

DOI： 10.1088/1757-899X/18/22/222015

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Language：English   Publishing type：Research paper (international conference proceedings)  

Sodium borosilicate glasses containing P2O5 and Al2O3 were prepared, and the behavior of phosphorus associated with the phase separation and the effect of Al2O 3 addition have been investigated. After the heat treatment, phase separation by spinodal decomposition was observed in the all samples. In the Al2O3-free glasses, phosphorus was preferentially distributed into B2O3-rich glass phase after the phase separation. With increasing Al2O3 content, the amount of phosphorus distributed into SiO2-rich glass phase increased. According to 31P MAS NMR measurements, in the Al2O 3-containing glasses, Q4 units free from terminal oxygen atoms were formed. It was suggested that the distribution of phosphorus depend on the PO4 units. © 2011 Ceramic Society of Japan.

DOI： 10.1088/1757-899X/18/11/112022

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

Li+ and H+ ions were electrochemically inserted into amorphous WO3 films prepared on an ITO-coated glass substrate by an R. F. magnetron sputtering method under Ar/O-2 flow ratios of 4/1 (SP1) and 1/1 (SP2). The cation distribution was estimated indirectly by depth profiles of refractive-index obtained from prism coupler measurements and was evaluated directly by glow discharge spectrometry (GDS). H+ ions inserted were segregated only at deeper region around ITO electrode, which was independent to the preparing condition. In the case of Li+ insertion into SP1 film, Li+ ions were initially segregated at around ITO electrode, and after further insertions, they were also distributed at around the surface of WO3 film. In SP1 film, Li+ ions at around ITO electrode seemed to contribute to coloration. In SP2 film, however, Li+ ions subsequently inserted, which were uniformly distributed in the film, were only involved in coloration. The difference in depth distribution and coloration was due to the difference in atomic structure of WO3 films.

DOI： 10.1088/1757-899X/18/9/092039

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Surface crystallized glass ceramics with fresnoite (Ba2TiSi 2O8) phase were prepared by conventional heat treatment of 30BaO-20TiO2-50SiO2 glass together with ultrasonic surface treatment (UST) technique. The precursor glass was fully crystallized in a bulk form without any cracks, and the optical transparency and crystallographic orientation of the crystalline layers were evaluated by UV-Vis spectroscopy and XRD diffraction analyses, respectively. These properties were both enhanced significantly by applying UST using fresnoite/water suspension before the crystallization process, which is advantage for nonlinear optical applications of bulk glass ceramics. The effects of UST on the crystallization behavior were investigated by applying UST with various conditions. © 2011 Ceramic Society of Japan.

DOI： 10.1088/1757-899X/18/11/112015

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Glasses based on lead oxide have excellent properties in general such as low melting point, high chemical durability and high stability of glassy form, which are suitable for the preservation of volatile nuclear wastes in a permanent vitrified form. In order to confirm the long-term performance of lead borate based glasses it is necessary to establish dissolution and diffusion processes based on a reliable model of the glass structure. In the present study molecular dynamics (MD) simulation of lead borate based glasses was carried out introducing a dummy negative point charge to reproduce asymmetric PbO n units. Parameters for the dummy charge were optimized based on the comparison between calculated radial distribution function and experimental one. Asymmetric coordination around Pb, for example trigonal bipyramid, was successfully reproduced in the MD simulated binary and ternary glass models. The simple model using the dummy charge was confirmed to be valid for further simulations of multicomponent glasses containing nuclear wastes and heavy elements. © 2011 Ceramic Society of Japan.

DOI： 10.1088/1757-899X/18/2/022014

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Language：English   Publishing type：Research paper (international conference proceedings)  

The planar waveguides of 12Na2O10NbO2.525WO 353TeO2+1Er2O3 ([NbWEr]) glasses were prepared by Ag+-Na+ ion-exchange at 320-380°C for 5-30 h. The optical properties of the waveguides were characterized. Waveguiding property was successfully confirmed under all the ion-exchange conditions in this study. The thickness of the waveguides increased with increasing ion-exchange temperature and time. The minimum propagation loss of the waveguides was approximately 0.8 dB/cm at 632.8 nm. Hence, the [NbWEr] glass waveguides were considered to be promising for broadband optical amplifiers. © 2011 Ceramic Society of Japan.

DOI： 10.1088/1757-899X/18/11/112018

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

A 10Na(2)S center dot 30B(2)O(3)center dot 60SiO(2) (mol %) glass was prepared, and the changes in glass structure and chemical state of sulfur caused by phase separation were investigated. In the as-prepared and heat-treated glasses, sulfur was present as S2- anion and polysulfide S2- and S3- anions, and Si-S and B-S bonds were not confirmed. A phase separation by spinodal decomposition was observed after heat-treatment, where sulfur was preferentially distributed to borate-rich phase. Even after the phase separation, formation of non-bridging oxygen was not recognized. The preferential distribution of sulfur anions in the present glass was explainable on the basis of the change in population of sodium ions, which compensated the negatively-charged sulfur anions. (C)2010 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.118.603

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The authors describe progress in the development of low temperature vitrification with BiPbO2I (BPI) as a promising immobilization technique by which Iodine-129 is recovered by BiPbO2NO3 to form BPI, and then solidified into a lead-boron-zinc glass matrix (PbO-B2O3-ZnO) using a low temperature vitrification process. The microscopic structure of BPI glass was analyzed by various analytical techniques, such as XRD (X-ray diffraction), NMR (nuclear magnetic resonance analysis), and XPS (X-ray photoelectron spectroscopy), using several types of glass samples. The results obtained provide structural information on key elements in BPI glass and can be applied for modeling the structure of the BPI glass, simulated by molecular dynamics. The previous work suggested that the leaching behavior of iodine from BPI glass depended upon the chemical conditions of the solution. Further leaching tests using solutions under varying conditions were carried out in order to predict mechanisms of iodine leaching. Normalized elemental mass loss values of iodine in simulated seawater and bentonite pore water are almost the same as those of boron, showing that iodine dissolves congruently with BPI glass, whereas iodine dissolves incongruently in Ca(OH)(2) solutions of pH 9 and 11. To demonstrate the feasibility of the BPI vitrification process, recovery tests of iodine from spent iodine filters were conducted and a prototype melting furnace was developed for scale-up tests of glass sample. It was found that more than 95% of iodine can be recovered from the spent iodine filter and that the prototype furnace can produce approximately 0.5 liters of homogeneous glass.

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

A chemical recycling method by using phase separation was applied to municipal waste slags. Glasses were prepared from incineration ash and ash-melted slag, where B2O3 was added to promote phase separation. The glasses were heat-treated at temperatures higher than their glass transition temperatures, and they were soaked in hydrochloric acid, leaching CaO, Fe2O3, K2O, and S. Transparent and colorless solids containing ca. 80 mass% of SiO2 were successfully obtained as residues. It was suggested that phase separation took place not in the heat-treatment but in the vitrification process, and further characterizations are however required to investigate the phenomena at microscopic levels in the recycling processes. (C) 2009 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.117.1195

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC GLASS TECHNOLOGY  

Borosilicate cluster models were constructed, and the Si-21 NMR chemical shift was estimated by molecular orbital calculations. For Q(4) species (an SiO4 unit consisting of four bridging oxygen atoms), a higher frequency shift was confirmed due to the replacement of the surrounding SiO4 with BO4 units, and for Q(4) species associated with more than one BO4 unit, the chemical shifts were nearly identical to those for Q(3) species (an SiO4 unit including one nonbridging oxygen) in alkali silicates. The chemical shifts of Q(4) species in borosilicates were interpreted in terms of the change in bond angle of Si-O-(Si,B4) bridges. A change in chemical shift anisotropy of Q(4) species was also found. The Q(4) species associated with two BO4 units indicated an anisotropy maximum, which was smaller than the anisotropy of Q(3) species.

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC GLASS TECHNOLOGY  

Various quaternary borosilicate glasses in the general system M(2)O-M'O-Al(2)O(3)-B(2)O(3)SiO(2) (M=Li, Na or K; M'=Ca, Sr or Ba) were prepared, and the concentration of four-fold coordinated boron (B4) atoms was determined using (11)B magic angle spinning NMR. Regression analyses were performed to predict the B4 fraction, in which B4 fraction and glass basicity were used as dependent and independent variables, respectively. Except for Al(2)O(3)-containing glasses, regression formulae giving high correlation coefficients were successfully obtained by using B4/(B+Sixf) (where f is a tunable coefficient) as the dependent variable. As for the glasses containing Al(2)O(3), however, the necessity of a different dependent variable was indicated.

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Borosilicate cluster models were constructed, and the 29Si NMR chemical shift was estimated by molecular orbital calculations. For Q 4 species (an SiO4 unit consisting of four bridging oxygen atoms), a higher frequency shift was confirmed due to the replacement of the surrounding SiO4 with BO4 units, and for Q4 species associated with more than one BO4 unit, the chemical shifts were nearly identical to those for Q3 species (an SiO4 unit including one nonbridging oxygen) in alkali silicates. The chemical shifts of Q4 species in borosilicates were interpreted in terms of the change in bond angle of Si-O-(Si,B4) bridges. A change in chemical shift anisotropy of Q4 species was also found. The Q4 species associated with two BO4 units indicated an anisotropy maximum, which was smaller than the anisotropy of Q3 species.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN ASSOC CRYSTAL GROWTH, INC  

Ternary alkali borosilicate glasses containing sulfur were prepared by a conventional melt quenching method, and their chemical bonding states were investigated based on XPS and Si-29,B-II MAS-NMR measurement. The glass samples changed in color from blue to reddish brown due to the state of the sulfur and their glass compositions. From S2p photoelectron spectra, it can be seen that the sulfur exists with a negative charge in the glass. The forming of non-bridging oxygen components was observed from O1s photoelectron spectra of the glasses, which colored to brown and reddish brown. Furthermore, a signal from silicon atoms coordinated to the sulfur was detected in these glasses by the Si-29 MAS-NMR measurement. From these results, it is considered that sulfur atoms bonded silicon atoms at the forming range of the non-bridging oxygen component.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

A chemical recycling process using phase separation of glass was applied to a granulated blast furnace slag with high CaO content. Glasses were prepared by adding B2O3 to the slag in order to promote phase separation, and the glasses were heat-treated above glass transition temperature. In the subsequent acid-treatment, however, gelation due to the elution of SiO2 phase containing CaO occurred, not obtaining high SiO2 Solids. Then, pretreatment was introduced to reduce CaO content in slag, where the raw slag was briefly washed in acid. The slag glasses prepared from the pretreated slag were commonly phase-separated by heat-treatment regardless of B2O3 content. After subsequent acid-treatment, colorless insoluble solids were successfully recovered. The end products consist of 70-90 mass% SiO2, and coloring ions such as Mn, Fe and Cr were almost completely removed from the slag glasses. Reutilization as raw materials for glass is expected.

DOI： 10.2109/jcersj2.116.220

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The planar waveguides of 12Na(2)O center dot 35WO(3) center dot 53TeO(2) center dot 1Er(2)O(3) glass (in mol%) were prepared by Ag+-Na+ ion-exchange at 300-360 degrees C for 5-30 h. The effective mode indices and propagation losses of the waveguides were measured at the wavelengths of 473, 632.8, 983.1 and 1548 nm by means of a prism coupler technique. The waveguide depths from glass surface increased with increasing ion-exchange temperature and time. The diffusion parameters such as diffusion coefficient and activation energy were calculated on the basis of an Arrhenius temperature dependence of the diffusion coefficient of Ag+ ions in the ion-exchanged glasses. The propagation losses of the waveguides were 5.04-6.64, 2.70-4.77, 5.44-6.73 and 7.32-8.31 dB/cm in the first half in the propagation distance from 0 to 3.0 cm and 3.52-4.82, 1.92-2.99, 3.78-5.06 and 3.91-5.15 dB/cm in the latter half at 473, 632.8, 983.1 and 1548 nm, respectively. The relationship between the optical properties of the waveguides and the ion-exchange conditions is discussed. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2007.01.010

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The sol-gel method was applied to create Al2O 3-Cr2O3 ceramics using aluminum ethylacetoacetate diisopropylate and chromium (III) chloride hexahydrate as starting materials. In the calcination at 600-1200°C it was found that the grains of Cr2O3-rich solid solution grew when they were exposed to the surrounding Al2O3-rich amorphous particles. The composition of the powders obtained by the sol-gel process changed with calcining temperature. Cr2O3-rich solid solutions firstly crystallize at low temperature and the composition of the crystallites changes as the crystals grow and react with the surrounding Al2O 3-rich phases. The final sintered bodies fired under an Ar atmosphere showed higher relative densities as compared with those fired in air. A dense sintered body was not obtained when abnormal grains grew when calcining occurred. © 2007 The Society of Materials Science.

DOI： 10.2472/jsms.56.526

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The planar waveguide of 12Na(2)O-35WO(3)(.)53TeO(2)lEr(2)O(3) glass (in mol%) was prepared by Ag+-Na+ ion-exchange at 330 degrees C for 5 h. The effective mode indices and propagation losses of the waveguide at the wavelengths of 473, 632.8, 983.1 and 1548 nin for TE and TM modes were measured by means of a prism coupler technique. The results were compared with those of a planar waveguide of the tungsten tellurite glass without Er3+ ions. Especially, the propagation losses of ion-exchanged tellurite glass waveguides were estimated for the first time to the best of our knowledge. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2006.03.024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The Si-29 MAS NMR spectra of P2O5-SiO2 binary glasses were measured before and after annealing to examine the local structure around Si atoms in the glasses. The glasses were composed of SiO6 octahedra and Q(4) (SiO4 tetrahedra with four bridging oxygens). By increasing the P2O5 content, the fractions of SiO6 octahedra increased and those of Q4 decreased. The fractions of SiO6 octahedra increased by 6-8% in the range of 29.7 to 47.4 mol % P2O5 by annealing for 5 h. This result was found for the first time in binary glasses. On the basis of the results obtained, the local structure around Si atoms in the glasses and the structural change by annealing are discussed.

DOI： 10.1246/cl.2006.1268

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Ceramic Society of Japan  

Ternary alkali borosilicate glasses containing sulfur were prepared by conventional melt quenching method, and their chemical bonding states were investigated based on X-ray Photoelectron Spectroscopy (XPS) and 29Si, 11B Magic Angle Spinning (MAS)-Nuclear Magnetic Resonance (NMR) measurement. The glass samples changed in color from blue to reddish brown due to the remaining sulfur and their glass compositions. These phenomena is closely related with the glass structure. From S2p photoelectron spectra, it can be seen that the sulfur exists with a negative charge in the glass. The formation of non-bridging oxygen components was observed from O1s photoelectron spectra of the glasses, which colored to brown and reddish brown. Furthermore, the signal of silicon atoms coordinated to the sulfur was detected in these glasses by the 29Si MAS-NMR measurement. From these results, it was considered that sulfur atoms bonded silicon atoms at the formation range of non-bridging oxygen component, and the bond of silicon to sulfur in the glasses caused the change in the sample coloration.

DOI： 10.2109/jcersj.114.697

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The hardening mechanism of refractory patching materials with a phosphate binder was investigated by means of 31P static and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Ten refractory patching materials were made of refractory powders of SiO 2 and fused alumina and five mixed solutions of phosphoric acid and aluminum biphosphate as phosphate binders. 31P static and MAS NMR spectra were measured of five phosphate binders and twenty soft and hard refractory patching materials, respectively, to reveal the local structure around P atoms. The 31P static and MAS NMR spectra revealed that PO 4 tetrahedra in the phosphate binders have no P-O-P linkage between PO 4 tetrahedra and that as the patching materials become hard, the ratio of PO 4 tetrahedra with bridging oxygens increases, respectively. This result suggests that the hardening of the patching materials is caused by the condensation of the phosphate binder. But the ratio of PO 4 tetrahedra with bridging oxygens was not enough to form the network by P-O-P linkage between PO 4 tetrahedra. On the basis of these results, the hardening mechanism of refractory patching materials with a phosphate binder is proposed.

DOI： 10.2472/jsms.55.670

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Local structure around oxygen is directly elucidated by 17O nuclear magnetic resonance (NMR). However, the 17O NMR spectra in borosilicate glasses are quite complicated, and hence the assignments of the peaks have been empirically done. In the present study, 17O NMR parameters for the various oxygen sites in the borosilicate system were obtained from the ab-initio molecular orbital calculations using the Gaussian03 programs. As for the oxygen atoms in SiOSi, SiOB[3], and B[3]OB[3] bridging bonds (B[n]: n-fold coordinated boron), the isotropic chemical shift δiO decreased with increasing the bond angle. The oxygen atoms coordinated by B[4] as SiOB[4], B[3]OB[4], and B[4]OB[4] bridges showed weak dependency in δiO against the bond angle, and B[4]OB[4] showed a maximum in δiO at 150°. The quadrupole coupling constant Cq of all the bridging oxygens increased with increasing the bond angle. When the oxygen atoms in SiOB[4], B[3]OB[4] bridges were coordinated by Na ion, δi O decreased by 5 ∼ 10 ppm. The oxygen atoms in trimeric ring clusters showed different δiO from dimeric clusters, indicating that δiO was also influenced by the second neighboring cations. The order of δiO was expected as SiOSi &lt
SiOB[4] &lt
SiOB[3] &lt
B[4]OB[4] &lt
B[3]OB[4] &lt
B[3]OB[3], which was in accordance with the order of bond covalency.

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O1s binding energy measured by X-ray photoelectron spectroscopy (XPS) is candidate as a new tool to determine a new scale of Lewis basicity of oxide ions in glass. Some mathematical expressions for the basicity or XPS chemical shift, such as charge parameter and optical basicity, were compared with the experimental O1s binding energy in binary alkali oxide glasses. The expressions so far in use needed some modification in parameters. A new empirical expression introduced in this paper gives a new concept and universal scale of basicity.

DOI： 10.2109/jcersj.113.44

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DOI： 10.14853/pcersj.2005s.0.468.0

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DOI： 10.14852/jcersjsuppl.112.0.S1250.0

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In Si-29-NMR, it has so far been accepted that the chemical shifts of Q(n) Species (SiO4 units containing n bridging oxygens) were equivalent between alkali borosilicate, and boron-free alkali silicate classes. In the sodium borosilicate glasses with low sodium content. however. a contradiction was confirmed in the estimation of alkali distributions B-11 NMR suggested that Na ions were entirely distributed to berate groups to form BO4 units, whereas a -90 ppm component Was also observed in Si-29-NMR spectra, which has been attributed to Q(3) species associated with a nonbridging oxygen (NBO). Then. cluster molecular orbital calculations were performed to interpret the -90 ppm component in the borosilicate, glasses. It Was found that a silicon atom which had two tetrahedral borons (B4) as its second nearest neighbors was similar in atomic charge and Si2p energy to the Q(3) species in boron-free alkali silicates. Unequal distribution of electrons in Si-O-B4 bridging bonds was also found. where much electrons Were localized oil the Si-O bonds. It was finally concluded that the Si-O-B4 bridges with narrow bond angle were responsible for the -90 ppm Si-29 component in the borosilicate glasses. There still remained another interpretation: the Q(3) species were actually present in the glasses. and NBOs in the Q(3) species were derived from the tricluster groups. such as (O3Si)O(BO3)(2). In the classes With low sodium content. however. it was concluded that the tricluster groups were not so abundant to contribute to the -90 ppm component. Copyright (C) 2004 Elsevier Ltd.

DOI： 10.1016/j.gca.2004.05.042

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The structural changes in amorphous WO3 films were investigated both on the atomic and electronic levels, and the experimental findings were interpreted using molecular orbital calculations. Electrochemical fast intercalation resulted in the splitting of a peak in the valence band region of the X-ray photoelectron spectrum. This splitting could be attributed to the formation of non-bridging oxygen. Decomposition Of WO6 units into WO4 units could also be inferred from the data. This decomposition was, however, not responsible for the split of the photoelectron peak. From the population analyses it was found that the average bond strength decreased due to the intercalation, while select W-O bonds increased in strength. It was expected that these changes in the chemical bonding character lead to localization of electrons and distortion of WO6 units, which was consistent with the theoretical interpretations of electrochromism, the intervalence charge transfer model and the small polaron absorption theory. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0040-6090(03)01188-X

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The alkali distribution in borosilicate glass has been discussed on the basis of the different quantities obtained by various experimental methods. The NBO fraction was chosen as a common quantity for evaluating the alkali distribution models. The NBO fractions in sodium borosilicate glasses were estimated from B-11 and Si-29 NMR as well as XPS. However, the best model was not found among the existing models. The amounts of sodium oxide consumed for the NBO formation in borate and silicate networks and for the formation of BO4 units were separately estimated from the B-11 and Si-29 NMR data. A new trend was found in the alkali distribution suggesting the possibility for a new universal distribution model.

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The structure of (100 -lambda)Bi2O3 . xLi(2)O (25less than or equal toxless than or equal to35 mol%) glasses has been investigated by means of X-ray and neutron scattering methods. Comparing the glasses with several bismuthate crystals in total correlation function T(r), it is concluded that a large amount of edge-sharing BiOn polyhedra are present in the glasses and the network structure is similar to the Bi2O4 crystal. In the crystal, BiO6 octahedra form a layer sharing their four corners mutually, and the BiO4+4 distorted polyhedra are placed between the layers sharing all the edges with the neighboring polyhedra. Assuming two different Li sites in the Bi2O4-based structure, structural models were constructed to compare T(r), from which it was suggested that some Li ions substituted for the octahedral Bi site and some occupied an interstitial vacant site, In addition, the glasses have various defects such as excess 0 ions, positive-holes on 0 ions, vacant space to accept atmospheric oxygens, and Bi vacancies. The glass formation is sensitive to the melting conditions, such as temperature and period, suggesting that there exists some optimum quantity in the defect structures. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(01)00921-8

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X-ray photoelectron spectra of RNa2O . B2O3 . KSiO2 (R = 0.2 to 5.0, K = 0.5 to 6.0) glasses were measured by a monochromatised Al-Ka XPS instrument. Chemical shifts of the core-level photoelectron spectra of the glass constituent ions were investigated. Peaks at the higher and lower energy sides of an Ols signal were ascribed to bridging oxide (BO) and non-bridging oxide (NBO) components, respectively. The BO component could not be separated into the oxide ions with different environment such as Si-O-Si, B-O-Si and B-O-B. Na1s signal could not be separated into two components of Na+ ions associated with [BO4/2](-) tetrahedron and NBO. For the small K values (=0.5 and 1.0), the NBO fractions measured by XPS agreed very well with the structural model proposed by Dell et al. [J. Non-Cryst. Soilds 58 (1983) 1], where NBO did not appear until R = 0.5 regardless of K values. With increasing K, however, the dependence of the NBO fraction upon R gradually came to disagree with the Dell model. At smaller R values than Rv = 0.5 +K/16, the NBO component already appeared to a considerable extent and the discrepancy between the XPS results and the Dell model became more significant with increasing K. This fact meant that additional sodium oxides were shared proportionally between silicate and borate networks even at the small R when K was larger than 2. A new sharing model was proposed on the basis of an acid-base concept. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(01)00720-7

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The electron paramagnetic resonance signals attributed to the triplet state of the positive-hole pairs on oxide ions are observed in (100-x) Bi2O3. xLi(2)O glass (x = 25, 30, 35 mol%). So far as we know, this is the first experimental observation of the triplet oxygen hole center in oxide glasses.

DOI： 10.1246/cl.2001.156

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The structure of Na2O-GeO2 glasses has been investigated, using molecular dynamics (MD) simulations based on an empirical three-body interaction model. A multi-body potential function with two energy minima in the angular term for a given three-atom unit was introduced to permit a transformation between different coordination states, such as 4- and 6-fold coordinated Ge sites. Parameters in the potential function were optimized with a non-linear least-squares (NLS) method. The optimal parameter set obtained with a Na4Ge9O20 crystal was employed for the structural models of pure GeO2 and 2Na2O·9GeO2 glasses. In the model for the binary glass, however, a number of 5-fold coordinated Ge, non-bridging O and 3-fold coordinated O formed. Another binary model free from 5-fold Ge was prepared using a simple scheme in which no three-body interaction was applied to the structural units containing 5-fold coordinated Ge. All the structural models produced showed good agreement with the experiments, including vibrational spectra and radial distribution functions (RDFs). No significant difference between the experimental observables of the two binary glass models was revealed, except for the coordination environment of Ge. This is because 5- and 6-fold Ge do not occur in a discrete arrangement through a corner-sharing of GeO4, e.g. GeO5,6-GeO4-GeO5,6, but in a dense configuration, e.g. as edge-sharing GeO5,6-GeO5,6, forming smaller rings than those in pure GeO2 glass.

DOI： 10.1016/S0022-3093(00)00313-6

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X-ray photoelectron spectra of Na2O Al2O3-SiO2 glasses were measured by a monochromatised Al-k alpha XPS instrument with a novel charge control method Chemical shifts of cove level photoelectron spectra of the glass constituent ions were investigated with glass composition with respect to the external energy reference of Au 4f(7/2). Peaks at higher and lower energy sides of the Ols signal were observed and they were ascribed to bridging oxide (BO) and nonbridging oxide (NBO) components, respectively The BO component was successfully separated into two parts: Si-O Si (BO(1)) and Al-O-Si (BO(2)). The compositional change for the relative amount of the three O1s components follows an equation derived from an assumption that all aluminium ions were four-coordinated. The Na1s signal could not be separated into two components of Na+ ions associated with [AlO4/2](-) tetrahedra and NBOs. However, the Na1s chemical shift reflected the change in the bonding characteristics of Na+ ions in the glasses.

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Photoluminescence (PL) of Er3+ doped in xNaO(0.05)-xNbO(2.5)-(100 - 2x)SiO2 (mol%) (x = 24, 27, 30, 33, 36) glasses was investigated before and after crystallization. After crystallization, Er3+ was determined to be in the glass phase. Following the precipitation of the NaNbO3 crystalline phase in these glasses, PL intensity of S-4(3/2) --> I-4(15/2) transition of Er3+ increased. A maximum of >100-fold increment in the PL intensity was observed after crystallization as compared with that of the uncrystallized glass. The mechanism of augmentation of the PL intensity is discussed in terms of the theory of PL intensity. We assume that the difference in the refractive index between the residual glass and crystallized phases was a dominant factor causing the increase of the PL intensity after crystallization. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(99)00525-6

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Surface crystallization of LiNbO3 on xK(2)O .(35-x)Li2O . 30Nb(2)O(5). 35SiO(2) (0 less than or equal to x less than or equal to 35) (mol%) glasses was investigated. The c-axis orientation of surface crystallized LiNbO3 was Improved when the glass contained 10 mol% K2O. Furthermore, Li ions in the LiNbO3 crystallites were partially replaced by K ions from the glass. Transparent surface crystallized LiNbO3 films on glasses were prepared by controlled heat treatment, which showed optical second harmonic generation. The estimated second-order non-linear optical susceptibilities were d(33) = 6.40 pm/V and d(31) = d(21) = d(34) = d(15) = 1/3d(33) = 2.14 pm/V for a film 1.33 mu m in thickness prepared after heating at 620 degrees C for 3 h, when the c-axis oriented film was described by a space group C-infinity v. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(99)00502-5

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The compositional dependences of Judd-Ofelt intensity parameters Omega(t) with t=2,4,6 of Er3+ were investigated systematically in xN(n)2O .(40-x)B2O3. 60SiO(2). 0.25Er(2)O(3) (mol%) glasses. The value of Omega(2) reveals a maximum around 10 mol% Na2O, inconsistent with a maximum shown at a Na:B ratio of about I in some physical properties of sodium borosilicate glasses. Whereas those of Omega(4) and Omega(6), decrease monotonically, with increasing Na2O content. The compositional dependences of the intensity, parameters were also compared with those of silicate and borate glasses. It was found that the borosilicate glass compositions can be tailored to obtain those intensity parameter values in both silicate and borate glasses.

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InxNa(2)O . (40-x)B2O3 . 60SiO(2) (mol%) (x = 5,10,15,20,25,30) glasses with 0.25mol% Eu2O3 as additive, the local structure around Eu3+ was explored by employing the phonon sideband spectra of Eu3+ associated with the D-5(2) <--F-7(0), transition. It was found that the types and fraction of the structural units around Eu3+ varied with glass composition. Moreover, the B-O- vibrational mode of BO3 unit exists around Eu3+ when x ≤ 15, which is not present in the same composition glasses free of Eu3+. A greatest asymmetry in the surrounding, of Eu3+ occurs at x = 10, inconsistent with a maximum of some physical properties found in sodium. borosilicate glasses at a Na:B ratio of about unity. In addition, various structural units possess different coordination preference to Eu3+. The highest theoretical microscopic optical basicity on the oxygen atoms in these units was advocated as a criterion of the coordination preference, which successfully elucidated a series of coordination preference phenomena occurring in silicate, borate and borosilicate glasses.

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Two sodium borosilicate glasses containing Er3+ were isothermally heat treated for phase separation, followed by the formation of the droplet and interconnected textures, respectively. The effects of heat treatment condition and the phase separated texture on photoluminescence (PL) intensity of S-4(3/2) --> I-4(15/2) transition of Er3+ were studied. It was found that the PL intensity increased with phase separation developing in both glasses. Moreover, the maximum PL intensities obtained by the phase separation in both glasses are 8.5 and 4.1 times as high as those in the respective untreated samples, the droplet texture being superior to the interconnected one. The mechanism of augmentation of the PL intensity was discussed in terms of the derived expression of the PL intensity. It was supposed that the induced interface after phase separation, causing notable increase in the radiative decay rate from the S-4(3/2) to I-4(15/2) levels, was responsible for the significant enhancement in the PL intensity.

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Eu3+ containing 3Na(2)O . 42B(2)O(3). 55SiO(2) (mol%) glass was isothermally heat-treated for phase separation. The photoluminescence (PL) behavior of Eu3+ was investigated. It was found that PL intensity of D-5(0)-->F-7(2) transition of Eu3+ increases with evolution of phase separation. A maximum 6.5 times increment in the PL intensity can be obtained after phase separation as compared to that of the as-cast sample. Moreover, the maximum increment of the PL intensity seems to be related to the texture induced by phase separation, the droplet texture being superior to the interconnected one. The mechanism of augmentation of the PL intensity was interpreted in terms of the derived expression of the PL intensity. It was then suggested that the induced interface after phase separation, causing remarkable increase in light scattering intensity and therefore notable increase in the population of Eu3+ On the D-5(0) energy level, accounted for significant enhancement in the PL intensity. On the other hand, from the emission intensity ratio of D-5(0)-->F-7(2) to D-5(0)-F-7(1) transitions of Eu3+, it was estimated that Eu3+ partitioned into the berate-rich phase after phase separation.

DOI： 10.2109/jcersj.106.1043

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The 6NaO.31B(2)O(3).63SiO(2) (in mot%) glass was chosen. The photoluminescence(PL) characteristics of Eu3+ doped in the glass, which was subjected to different phase separated heat treatments, were investigated systematically, It was found that PL intensity of D-5(0)-->F-7(2) transition of Eu3+ increased with phase separation developing, Furthermore, the maximum PL intensities obtained by the different heat treatment processes seem to depend on the morphology induced by phase separation, the droplet morphology having the advantage over the interconnected one with the PL intensities of 6.4 and 5.5 times as high as that in the as-cast sample, respectively. The mechanism of enhancement of the PL intensity was then discussed on the basis of the derived expression of the PL intensity. It was concluded that the induced interface after phase separation, engendering significant increase in light scattering intensity and thereby notable increase in the population of Eu3+ on the D-5(0) energy level, accounted for considerable increase in the PL intensity. On the other hand, from the emission intensity ratio of the D-5(0)-->F-7(2) to D-5(0)-->F-7(1) transitions (R) of Eu3+, the phases into which Eu3+ segregated after various phase separation processes were estimated.

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X-ray photoelectron spectra were measured on the fresh surfaces of silica, binary alkali silicate and mixed alkali silicate glasses fractured in ultra-high vacuum by irradiating with focusing monochromatic Al K alpha X-ray. Binding energies and chemical shifts of Ols, Si2p, Li1s, Na1s, K2p, Rb3d(5/2) and Cs4d(5/2) have been investigated, and charge densities of oxide, silicon and other alkali ions have been discussed. For xNa(2)O .(100-x)SiO2 glasses, electron densities of bridging oxide ion (BO), non-bridging oxide ion (NBO) and sodium ions increased with increasing the Na2O content, suggesting that the bond order between O2p and Na3s (or 3p) increased with increasing the Na2O content. In addition, the difference in binding energies between BO1s and NBO1s decreased with increasing Na2O content indicating that electrons were delocalized considerably in O2p-Si3d pi bonds, For 33.3R(2)O . 66.7SiO(2) (R = Li, Na, K, Rb, Cs) glasses, charge densities of BO increased with increasing ionic radius of alkali ions (Li-->Na-->K, Rb-->Cs). The degree of polarization of BO increased with increasing ionic radius of alkali ions, For 33.3 ((1-y)Li2O . yCs(2)O]. 66.7SiO(2) glasses, O1s peak of NBO could not been discriminated between the components belonging to Si-O-... Li+ and Si-O-... Cs+, Ols chemical shifts of 33.3((1-x)Li2O . xCs(2)O}. 66.7SiO(2) glasses with increasing Cs2O content were similar to the shifts of 33.3R(2)O.66.7SiO(2) glasses with increasing ionic radius of alkali ions. The area-weighed mean values of Ols peaks appeared to have good correlation with an empirical expression of optical basicity.

DOI： 10.2109/jcersj.106.415

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The structure and electronic states of Na_2S-SiO_2 oxysulfide glasses were investigated and the role of sulfur in the glasses is discussed. Na_2S formed stable glass with SiO_2 at an alkali concentration range similar to that of Na_2O-SiO_2 systems by the conventional melt-quench method. The obtained glasses were reddish brown in color and a remaining of sulfur was confirmed. X-ray photoelectron spectroscopy(XPS)was used to study the chemical bonding state of bridging and nonbridging anionic species in Na_2S-SiO_2 glass. The S2p binding energy of the glass was observed to be approximately 161 eV. This value is lower than that of orthorhombic crystalline sulfur and almost the same as the value of Na_2S. From the results, the electron density around sulfur was near to that of S^<2->. Furthermore, by ^<29>Si magic angle spinning(MAS)and unclear magnetic resonance(NMR)measurement, three clear-cut peaks were detected between 0 and -120 ppm. It was assumed that a sulfur atom was joined to silicon via substitution for an oxygen atom, and was present as nonbridging sulfur in Na_2S-SiO_2 glass with low alkali ion concentration. On the other hand, it was revealed that a portion of the sulfur ions existed in an isolated state from the glass-network structure at high alkali content. The glass composition changed to a chemical composition that was more silica rich than predicted. The sulfur ions made sulfide clusters with the sodium ions isolated from the glass-network.

DOI： 10.2109/jcersj.106.150

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The structure anal electronic states of Na2S-SiO2 oxysulfide glasses were investigated and the role of sulfur in the glasses is discussed. Na2S formed stable glass with SiO2 at an alkali concentration range similar to that of Na2O-SiO2 systems by the conventional melt-quench method. The obtained glasses were reddish brown in color and a remaining of sulfur was confirmed. X-ray photoelectron spectroscopy (XPS) was used to study the chemical bonding state of bridging and nonbridging anionic species in Na2S-SiO2 glass. The S2p binding energy of the glass was observed to be approximately 161 eV, This value is lower than that of orthorhombic crystalline sulfur and almost the same as the value of Na2S. From the results, the electron density around sulfur was near to that of S2-. Furthermore, by Si-29 magic angle spinning (MAS) and nuclear magnetic resonance (NMR) measurement, three clear-cut peal-rs were detected between 0 and -120 ppm. It was assumed that a sulfur atom was joined to silicon via substitution for an oxygen atom, and was present as nonbridging sulfur in Na2S-SiO2, glass with low alkali ion concentration. On the other hand, it was revealed that a portion of the sulfur ions existed in an isolated state from the glass-network structure at high alkali content. The glass composition changed to a chemical composition that was more silica rich than predicted. The sulfur ions made sulfide clusters with the sodium ions isolated from the glass-network.

DOI： 10.2109/jcersj.106.150

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A wavelet analysis of x-ray diffraction patterns is introduced for analyzing glass structures. The analysis indicates that within a short distance (∼0.8 nm for silica glass) atoms in the glass are arranged around the most probable positions which are almost as regular as the equilibrium positions in crystal. However, in glass the atomic distribution around the most probable position increases exponentially with increasing interatomic distance (exponentially damped regularity), whereas the crystal does not have this kind of damping. Beyond this distance, it is difficult to determine the structure in atomic scale due to the large atomic distribution. But, the analysis shows that the arrangement of quasiatomic planes in glass is still statistically regular (with damped regularity) up to an intermediate distance, e.g., 2.5-3.0 nm for silica glass. Then glass structure might be quantitatively determined by means of the structure of corresponding crystals and of the extent of the distributions around the most probable positions for atoms, as well as of the sizes of the structurally correlated group. © 1998 The American Physical Society.

DOI： 10.1103/PhysRevB.58.14279

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The reason for the optical frequency doubling in the 70Ga2S3-30La2S3 glass is investigated. The tetragonal Ga6La10/3S14 phase due to crystallization of the glass is responsible for the frequency doubling. Dense and transparent Ga6La10/3S14 crystalline thin films have been prepared by means of the controlled surface treatment of the glass due to an ultrasonic surface treatment. The effective second-order nonlinear optical susceptibilities of the crystalline thin films are analyzed. © 1998 American Institute of Physics.

DOI： 10.1063/1.121985

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Wavelet analysis of X-ray diffraction patterns was made for structures of silica glasses manufactured by electrical fusion, oxy-hydrogen flame fusion of quartz powder, and flame hydrolysis of SiCl4. The analysis indicates that their structures were not affected by the manufacture methods. It is believed that there is a thermodynamically most favoured or unique structure for glass in an intermediate range up to a few nm. It is expected that amorphography (in analogy to crystallography for crystal) for glass will emerge as a new branch of science. According to our statistical crystallite model, glass structure could be determined by the crystallography of corresponding crystals and the damping with interatomic distance for the crystalline regularity. (C) 1997 Elsevier Science B.V.

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ZrO_2-dispersed MgO-Al_2O_3 ceramics with various MgO to Al_2O_3 compositional ratios were prepared from Mg(OH)_2 powder, α-Al_2O_3 powder and Zr-n-butoxide by calcining at 1000°C for 2h and sintering at 1600°C for 1h. The influence of the MgO-Al_2O_3 compositional ratio on the sinterability and mechanical properties was studied. Addition of 10 vol% ZrO_2 improved the relative density of the sintered specimens containing 50 and 62.5 mol% Al_2O_3. However, the addition was not effective at other compositional ratios. The bending strength was improved at composition containing more than 50 mol% Al_2O_3, Where the dispersed ZrO_2 Particles were in the form of tetragonal phase. The bending strength increased with increase in Al_2O_3 content in the ZrO_2 dispersed specimens. The fracture toughness was improved for all specimens by ZrO_2 dispersion, especially, for the specimen in which MgO-Al_2O_3 component was in a single crystalline phase.

DOI： 10.2109/jcersj.105.588

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ZrO2-dispersed MgO-Al2O3 ceramics with various MgO to Al2O3 compositional ratios were prepared from Mg(OH)(2) powder, alpha Al2O3 powder and Zr-n-butoxide by calcining at 1000 degrees C for 2h and sintering at 1600 degrees C for 1h. The influence of the MgO-Al2O3 compositional ratio on the sinterability and mechanical properties was studied. Addition of 10 vol% ZrO2 improved the relative density of the sintered specimens containing 50 and 62.5 mol% Al2O3. However, the addition tvas not effective at other compositional ratios. The bending strength was improved at composition containing more than 50 mol% Al2O3, where the dispersed ZrO2 particles were in the form of tetragonal phase. The bending strength increased with increase in Al2O3 content in the ZrO2 dispersed specimens. The fracture toughness was improved for all specimens by ZrO2 dispersion, especially, for the specimen in which MgO-Al2O3 component was in a single crystalline phase.

DOI： 10.2109/jcersj.105.588

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Photochromic properties were investigated for glass in the system CdO-Bi2O3-Al2O3. Optical density increased with increasing BiO1.5 content in the glasses at fixed CdO content. The darkening degree could be effectively enhanced by oxidation treatments. The composition dependence and effect of oxidation treatment were studied by X-ray photoelectron and Raman scattering spectroscopies. With increasing BiO1.5 content the Lewis basicity of oxygen atoms increased and the fraction of covalently bonded cadmium decreased. The trap density of holes increased and the photogeneration yield decreased. The darkening degree showed a maximum around BiO1.5=13 cation%. The effect of oxidation treatment on the darkening degree may be related to production of a large amount of monovalent O- ions with holes in their 2p valence band, and to formation of electron centers in cadmium atoms.

DOI： 10.2109/jcersj.105.322

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X-ray photoelectron spectra of R2O-TeO2 (R: Li, Na, K, Rb and Cs) glasses were measured, using a fresh surface fractured in an ultra high vacuum (≈ 7 × 10-8 Pa) and irradiated with a monochromatic Al K α X-ray (hv = 1486.6 eV). The O 1s photoelectron spectra showed only a single Gaussian-Lorentzian peak and the peak shifted toward smaller binding energy with increase in Lewis basicity of oxide ions in the glasses. Two peaks attributed to BO and NBO were not observed. In the near valence band spectra for the lithium tellurite glasses, the spectral profile gradually became similar to that of a Li2TeO3 crystal with increase in Li2O content up to 30 mol% Li2O. This variation of the profile is correlated to the change in the coordination structure of the tellurium atoms (TeO4 trigonal bipyramids → TeO3 trigonal pyramids) with the addition of the alkali oxides.

DOI： 10.1016/S0022-3093(96)00628-X

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Photochromic properties were investigated for glass in the system CdO-Bi2O3-Al2O3. Optical density increased with increasing BiO1.5 content in the glasses at fixed CdO content. The darkening degree could be effectively enhanced by oxidation treatments. The composition dependence and effect of oxidation treatment were studied by X-ray photoelectron and Raman scattering spectroscopies. With increasing BiO1.5 content the Lewis basicity of oxygen atoms increased and the fraction of covalently bonded cadmium decreased. The trap density of holes increased and the photogeneration yield decreased. The darkening degree showed a maximum around BiO1.5=13 cation%. The effect of oxidation treatment on the darkening degree may be related to production of a large amount of monovalent O- ions with holes in their 2p valence band, and to formation of electron centers in cadmium atoms.

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Color change and its mechanisms for glasses and glass-ceramics in the Bi_2O_3-CdO-Al_2O_3 system prepared under various melting and annealing conditions were investigated. It was suggested that brown color of the glasses with comparatively low Bi content which were obtained by melting at high temperatures was caused by metallic Bi while deep green color of the glasses with comparatively high Bi content resulted from Bi^<2+> and defects. The deep color of the glasses markedly faded after annealing treatments for long time. Formation of the transparent glass-ceramics was assumed to be related to the oxygen defects. Color of the glass-ceramics was explained in term of oxygen defects and crystalline phases formed by annealing treatments.

DOI： 10.2472/jsms.45.630

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Reversible thermochromic coloration was detected in Bi0(1.5)-CdO-AlO1.5 system glasses. The relevant parameters were strongly dependent on the BiO1.5 content. It was suggested that the weakened and more polarized Bi-O bond due to increased BiO1.5 content enhanced the thermochromism of the glasses. The redshift of absorption edges at room temperature and the increase in the temperature coefficient of the shift with increasing BiO1.5 content were analyzed. The thermochromic mechanism was explained in terms of the temperature dependence of the optical energy gap caused mainly by electron-phonon interaction.

DOI： 10.2109/jcersj.104.79

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Amorphous tungsten trioxide films were prepared from iso-polytungstic acid as a precursor and by RF magnetron sputtering method. Framework structure was investigated based on X-ray diffraction analyses, in which amplitude function as well as radial distribution function was used, And the previously reported films prepared by vacuum evaporation and an ion exchange method using Na2WO4 . 2H(2)O as a precursor were also re-examined. It was found that, in the films derived from iso-polytungstic acid, the framework had a similar manner to that in hexagonal-WO3 crystal, whose framework was constructed by 3-, 4- and 6-membered rings formed by WO6 octahedra. It was supposed that edge-sharing polyhedra and tungsten and/or WO6 defects were present in the as-prepared film and changed to corner-sharing connection and continuous framework by post-annealing. It was also suggested that structural water was present in a hexagonal tunnel in the framework. These structural characteristics were also observed in the films prepared by vacuum evaporation and ion exchange methods. As for the sputtered films, formation of two framework-types without structural water was confirmed. The hexagonal-WO3 like framework was formed in the films prepared under a low O-2 partial pressure, and tetragonal-WO3 like one with an ordinary ReO3-type structure made up with 4-membered rings was produced at a high O-2 pressure.

DOI： 10.2109/jcersj.103.222

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A-WO3 films have been synthesized from an isolated polytungstic acid as a precursor and by RF magnetron sputtering. Framework structure of the a-WO films is also re-investigated in detail based on X-ray diffraction analyses, from which some new structural information are obtained, such as the formation of novel frameworks and the defect structure of the framework.

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Amorphous tungsten trioxide thin films were prepared using a rf magnetron sputtering method. The relation between structure and electrochromic properties was investigated. At the macroscopic level, the films had dense structures. From Raman spectroscopic and X-ray radial distribution analyses, it was deduced that the networks were basically formed by three-, four- and six-membered rings of corner-sharing WO6 octahedra, and in the films with low O/W atomic ratios many edge-sharing units were present. It was also found that the films with high O/W ratios showed good electrochromic properties, which were closely related to the six-membered rings. © 1994.

DOI： 10.1016/0022-3093(94)90290-9

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Oxy-fluoride glasses in the GeO2PbOPbF2 system were prepared and their structure investigated using vibrational spectra, X-ray diffraction and Raman spectra methods. Structural models were constructed by molecular dynamics simulations. In the models obtained, glass networks were formed by GeO4 tetrahedra and Ge(O,F)5 and Ge(O,F)6 polyhedra. Lead entered the networks at PbFPb in the models with high Pb/Ge ratio. The presence of germanium with high coordination numbers of 5 and 6 was supported by radial distribution analyses. GeO bonds in GeO4 tetrahedra seemed to give bands between 650 and 850 cm-1 (non-bridging oxygen) and between 450 and 650, and between 850 and 950 cm-1 (bridging oxygen). GeO and GeF in Ge(O,F)n (n &gt
4) were supposed to contribute the bands observed between 350 and 550 cm-1 in the Raman spectra. © 1994.

DOI： 10.1016/0022-3093(94)90522-3

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New photochromic glasses in the system Al-Cd-O-F, Al-Cd-Pb-O-F and Al-Cd-Pb-O were obtained. Al-27 nuclear magnetic resonance spectra confirmed that both Al(4) tetrahedra and Al(6) octahedra coexisted in the glasses containing fluoride ions and the number of the latter increased, accompanied by an increase of the fraction of Al-F bonds, with increasing atomic ratio F/O. However, most fluorine is coordinated with the Al(6) octahedra. Photo-induced absorption decayed slowly, accompanied by luminescence, and its half-life period was about 10 h at room temperature in the dark. The possible color centers are discussed on the basis of electron spin resonance spectra.

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Coordination changes of Te(+IV) atoms were derived from Raman and X-ray photoelectron spectra of the binary tellurite glasses containing Li, Na, Ba and Zn. A structure model consistent with the experimental results was proposed. In this model, TeO4 units were converted mainly to O2/2Te-O and O1/2Te(=O)-O- in the range of lower atomic ratio O/Te, and the rate of increase of TeO3/TeO4 decreased in the range of higher O/Te because of the equilibrium TeO4/2 &lt;-&gt; O2/2Te=O. The increase in the fraction of non-bridging oxygen atoms and three-coordinated Te(+IV) atoms was confirmed by X-ray photoelectron spectra. The fraction of non-bridging oxygen estimated from X-ray photoelectron spectra agreed well with that from the Raman spectra and the model.

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CdTe microcrystallites were precipitated in 57.8CdO 19.7SiO(2) 19.OB2O3 3.5Al(2)O(3) glasses doped with 5.0 mol% CdTe. The microcrystallite size increased linearly with t(1/3) (t: heat-treatment time), indicating diffusion-controlled growth mechanism, where the estimated activation energy for diffusion was 542 kJ/mol. The linear increase in the band gap energy with 1/r(2) (r: the crystallite radius) suggested the quantum size effect of the CdTe microcrystallites.

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Thermal behavior of the Pb-substituted Bi-2223 phase was examined by characterizing samples annealed at 500 degrees C to 850 degrees C in air and also those subsequently reheated at 850 degrees C in air by XRD, SEM and magnetic measurements. Very interesting reactions occurred, which were segregation of precipitates on annealing below 830 degrees C and dissolution of the precipitates on subsequent reheating at 850 degrees C into the 2223 phase. The precipitates were identified as Sr2.5Bi0.5Pb3Ca2CuOz. The precipitation and the dissolution were clearly confirmed by morphological observations of a fixed portion of a sample before and after heat treatments. These results strongly suggest that the 2223 phase changes its composition reversibly between the relatively Pb-rich composition stabilized above 850 degrees C and relatively Pb-poor ones stabilized in essentially the same structure below 830 degrees C. However, T-c remained almost constant at 113K.

DOI： 10.1016/0921-4534(94)90388-3

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Precipitation of LaBO3 on the surface of a glass of composition 0.1Cr2O3·25Li2O·10La2O3·65B2O3 (in mol%) was enhanced due to ultrasonic surface treatment (UST) with aqueous and ethanol suspensions of LaBO3 particles. The aqueous suspension gave a higher efficiency than the ethanol suspension. The crystallites were almost uniform in size distribution, and grew irregularly: increase-decrease-increase in size when heated at 580°C. Preferred growth of (200) was detected. The mechanism of UST enhanced crystallization is proposed. © 1994, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.43.618

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New aluminate glasses were obtained with the conventional melt-quench technique in the system SrO-ZnO-Al_2O_3. The glass forming region was determined. The glasses were colorless and had good chemical durability in laboratory conditions. When irradiated with UV-light, a broad absorption was induced with a peak at 470 nm (2.64 eV) and an ESR signal (77 K and 300 K) was induced with an apparent g-value of 2.006. Both the changes in optical density and the intensity of the ESR signal increased with the ZnO content. From the characteristic of ESR signal, coloring of glass was concluded to be due to the formation of hole trapped on oxygen and electron center resting on zinc ions.

DOI： 10.2109/jcersj.101.99

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New aluminate glasses were obtained with the conventional melt-quench technique in the system SrO-ZnO-Al2O3. The glass forming region was determined. The glasses were colorless and had good chemical durability in laboratory conditions. When irradiated with UV-light, a broad absorption was induced with a peak at 470 nm (2.64 eV) and an ESR signal (77 K and 300 K) was induced with an apparent g-value of 2.006. Both the changes in optical density and the intensity of the ESR signal increased with the ZnO content. From the characteristic of ESR signal, coloring of glass was concluded to be due to the formation of hole trapped on oxygen and electron center resting on zinc ions.

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New aluminate glasses were obtained with the conventional melt-quench technique in the system SrO-ZnO-Al2O3. The glass forming region was determined. The glasses were colorless and had good chemical durability in laboratory conditions. When irradiated with UV-light, a broad absorption was induced with a peak at 470nm (2.64eV) and an ESR signal (77K and 300K) was induced with an apparent g-value of 2.006. Both the changes in optical density and the intensity of the ESR signal increased with the ZnO content. From the characteristic of ESR signal, coloring of glass was concluded to be due to the formation of hole trapped on oxygen and electron center resting on zinc ions.

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The 720 and 780 cm-1 components of the deconvoluted Raman spectra of glasses in the systems RnO-TeO2 (R=Li, Na, K, Ba, Zn) were attributed to TeO3 groups and the 665 cm-1 band was to TeO4 groups. The theoretical values of the molar ratio TeO3/TeO4 derived from an assumed vitrification reaction were compared with the ratio derived from the intensity ratios of the Raman bands, I(720) /I(665) and I(780)/I(665). It was indicated that [O2/2Te=O] and [O1/2Te(=O)-O]- units were induced by the addition of network modifying oxides in the composition range of lower atomic ratio O/Te. It was proposed that the decrease in the rate of increase of the ratio TeO3/TeO4 in the range of larger O/Te was due to the equilibrium TeO4/2↔[O12/2Te=O] favoring the former unit. © 1993, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.42.473

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The formation of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system has been studied in ground powder samples enclosed in silver pipes.The samples with a composition of Bi:Pb:Sr:Ca:Cu=0.9:0.2:1.0:1.0:1.6 prepared by heating at 850°C for 24h were mechanically ground for various periods, put into silver pipes and heated at 840-850°C.The formation of the high-Tc phase was found to be promoted in the samples enclosed in the silver pipes, depending upon three factors: grinding time, atmosphere in the pipe and reaction between the powder sample and the silver pipe.

DOI： 10.2497/jjspm.40.216

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The A 12p peak was found near 74.7 eV and F 1s peak was located near 68 3.7 eV for the glasses in the system Al-Cd-Pb-O-F. With the increase in the F/0 ratio, the F 1s binding energy decreased and that of Al 2p increased. It is concluded that most of F ions are under ionic interaction with Cd and Pb, and that the rest of F ions substitute 0 in AlX(n) polyhedra (n = 4 or 6; X = F + 0) as the F/0 ratio increases.

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The constitution of glasses in the systems M2O3-TeO2 (M = B and In) was investigated by Raman and infrared spectroscopy. From the relation between the M2O3 content and the intensity ratios of the deconvoluted Raman peaks I(720)/I(665) and I(780)/I(665), it was concluded that In2O3 behaves as a network modifier to yield TeO3- units and that discrete BO3 and BO4 units construct a network of glasses containing boron oxide. A structural model for those glasses was derived which involves three-coordinated oxygen atoms and TeO4 units of an intermediate configuration, O3Te(delta +) . . . O(delta -).

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TeK-edge spectra were measured for binary glasses of compositions 0.16B2O3.0.84TeO2 and 0.301B2O3.0.699TeO2. Te-O bond length and coordination number of Te atoms were analyzed to be very similar to those of paratellurite. Within errors of measurement, all the Te atoms were four-coordinated and TeO3+ units were absent in the glasses. It was concluded that some other mechanism should be present to compensate for a negative charge on four-coordinated boron atoms in the glasses.

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The local structure around iron atoms in four series of lithium tellurite glasses were studied by means of Mossbauer spectroscopy with Co-57(Pd) and Fe foil as the gamma-ray source and reference. All the spectra showed one symmetric doublet peak. Quadrupole splitting increased with increasing Fe2O3 content and ranged from 0.61 to 0.84 mm/s, whereas the isomer shift was almost independent of Fe2O3 content, ranging from 0.37 to 0.39 mm/s. Comparison of isomer shift and quadrupole splitting values with those of the relevant crystals showed that all the iron ions were trivalent and octahedrally coordinated. The increase in quadrupole splitting with Fe2O3 was attributed to an increase in the geometric distortion of the FeO6 octahedra. Linear correlation between quadrupole splitting and glass transition temperature was tentatively interpreted in terms of the relaxation of the Te-O framework.

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New photochromic glasses in the system Al-Cd-O-F were obtained. When this type ot glass was irradiated by darkening UV light having the wavelength near the absorption edge, a new absorption was induced almost over the whole visible region. The photo-induced absorption decayed very slowly accompanying luminescence, and its half fading time was remarkably shortened by heating. Infrared and 27Al MAS-NMR spectra indicated that both AlX4 tetrahedra and AlX6 pctahedra (X=O, F) were present and the fraction of octahedra increased with the increasing fluorine content. On the basis of both the ESR spectra and the glass structure model, the color centers were proposed to be oxygen hole centers. © 1992, The Society of Materials Science, Japan. All rights reserved.

DOI： 10.2472/jsms.41.578

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The effects of Li-addition to the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system have been studied for the samples with the nominal composition of Bi:Pb:Sr:Ca:(Cu, Li)=0.96:0.24:1.0:1.1:(1.6-x, x) heated at 840 to 845°C for 144h in air (x=0 to 0.2). The characterization of the samples has been made by DTA, the measurements of XRD and DC electrical resistivity, SEM observation and ICP analysis. The Li-addition promotes the formation of the high-Tc phase. The sample with x=0.05 heated at 842°C for 144h exhibits Tc=116K, while Tc=109K for the Li-free sample (x=0) heated at 842°C for 120h. The results of ICP analysis showed that the Li content of the samples heated at 842°C for 120h was very low.

DOI： 10.2497/jjspm.39.386

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Aqueous solutions of calcium nitrate stabilized with EDTA, ammonium dihydrogen orthophosphate and iron (III) nitrate were mixed before they were subject to ultrasonic spraying and to subsequent pyrolysis in an electric furnace, and particles of 0.45μm in average diameter consisting of hydroxyapatite and hematite were obtained. Surface morphology and microstructure of the particles were examined. A nucleus (hematite)-shell (hydroxyapatite) type structure was observed for larger particles (>0.8μm in diameter) though the particles of medium size apparently had a uniform microstructure. Such structural difference due to the particle size was explained in terms of decomposition of the Ca-EDTA chelating bond at lowest temperatures and temperature distribution in the sprayed mists.

DOI： 10.2497/jjspm.39.239

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Effects of the Li-addition to the high-T_c phase in the Bi-Pb-Sr-Ca-Cu-O system have been studied for samples with starting compositions of Bi:Pb:Sr:Ca:Cu:Li=0.9:0.2:1.0:1.0:1.6:x with x=0-0.10 and heated at 820-850°C for 40-96h. The temperature, at which an endothermic reaction occurred, lowered markedly as x increased. T_c was raised up to 116K for the sample with x=0.03 heated at 840°C for 48h, while a susceptibility measurement revealed that T_c=110K. The lattice constants, a and c, were independent of Li content. ICP analysis showed that the heat treated samples had very low Li content. The results suggest that a small amount of the high-T_c phase with T_c=116K forms on the surface of the high-T_c phase with T_c=110K.

DOI： 10.2497/jjspm.39.382

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Li addition was found to raise T_c up to 116K in the high-T_c phase in the Bi-Pb-Sr-Ca-Cu-O system. But the role and behavior of Li has not yet been clarified. This study has been done for samples with starting compositions of Bi_0.9Pb_0.2Sr_1.0Ca_1.0Cu_1.6Li_xO_y with x=0.03 to 0.10 and heated at 825 to 840°C for 1 to 48h. ICP analysis showed that Li content decreased with increasing sintering time. The lattice constant a decreased at first and then gradually increased. On the other hand, the lattice constant c passed through a maximum around 4h.

DOI： 10.2497/jjspm.39.767

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The BPSCCO powder with a nominal composition of Bi:Pb:Sr:Ca:Cu=0.96:0.24:1.0:1.1:1.6 prepared by the co-precipitation method was packed into a Ag tube. The tape was fabricated by plastic deformation. Optimized heat treatment conditions for the tape samples have been studied. The critical current density of the tape samples after the 3rd heat treatment was found to depend on the temperature of the 1st heat treatment. The maximum critical current density was 10, 500A/cm² at zero field and 77K in the sample subjected to the 1st heat treatment at 845°C. The impurity phases with a particle size of 5-10μm, such as Ca-Sr-Cu-O and Ca-Sr-Pb-O, were present even in the sample with Jc=10, 500A/cm².

DOI： 10.2497/jjspm.39.404

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Tantalum and niobium based amorphous solids were prepared by drying respective peroxo polyacids. Peroxo-polytantalate (Ta-IPA) was obtained by a direct reaction of Ta(OC2H5)5 with H2O2, and its Nb-analogue (Nb-IPA) was synthesized by dissolving metallic Nb in H2O2. Niobium carbide also gave a pale yellow solution (Nb-IPA) with H2O2, which had carbon incorporated as a hetero atom. Alternating current electrical conductivity measurements were carried out with pellet samples. Each specimen showed similar temperature dependency indicating its proton conductive mechanism was the same. The conductivity of Ta-IPA solid was larger than those of the others (e.g. 3.9×10-6 S cm-1, 27°C). Conduction mechanisms are discussed i relation to the water content and the structure of these materials. © 1992.

DOI： 10.1016/0167-2738(92)90282-T

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DOI： 10.1016/S0022-3093(05)80780-X

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DOI： 10.1016/S0022-3093(05)80776-8

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DOI： 10.1143/JPSJ.61.2224

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DOI： 10.1016/0040-6090(91)90486-H

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The structure of peroxotungstic acid (W-PTA) prepared from metallic W and aqueous H2O2 was investigated based on Raman, IR, and XRD analyses. W-PTA was an amorphous compound constructed of peroxo polytungstate anions, in which the anions were bound to each other through hydrogen bonding. RDF analyses suggested that the polyanion was W12O38(O2)16-6, in which a six-membered ring of corner-shared polyhedra, such as WO5(O2) or WO6, was sandwiched by two W3O10 units consisting of edge-shared WO6. © 1991.

DOI： 10.1016/0022-4596(91)90170-M

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The structure of amorphous tungsten trioxide films was investigated with IR and Raman spectroscopic analyses and an XRD method. The films were prepared by ion exchange from sodium tungstate as a starting material. Films consisted of microclusters of 10–30 Å diameter, in which the networks are formed with WO6 octahedra sharing their corners and edges. The networks in the as-prepared samples consisted of WO6 units with low symmetry, in which termination by W=O and W — OH2 groups was common. As the post-annealed temperature became higher, the symmetry of WO6 was improved and the edge-sharing octahedra disappeared. © 1991, Materials Research Society. All rights reserved.

DOI： 10.1557/JMR.1991.1324

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DOI： 10.1016/S0921-4534(05)80213-8

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DOI： 10.1111/j.1151-2916.1991.tb04076.x

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DOI： 10.1016/0022-4596(91)90177-J

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DOI： 10.1016/0167-2738(90)90149-L

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The X-ray diffraction intensity obtained using a thin-film diffractometer has a special angular dependence as a result of its optical arrangement, owing to the absorption of X-rays by a thin-film specimen. In this study we examined in detail the influence of a secondary soller slit and developed a method of date correction so as to produce good agreement between the observed and calculated dependence. This method has been successfully applied to a structural study of WO3 evaporated film specimens. © 1989, The Japan Society for Analytical Chemistry. All rights reserved.

DOI： 10.2116/analsci.5.257

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Microstructure of a-WO3 films prepared by electron beam vacuum evaporation was examined based on XRD. The peak positions in the observed PDFs corresponded with those in the PDFs calculated from the crystal structure of hexagonal WO3 and WO3 · 1 3H2O, and the framework structure of the films was therefore thought to consist of the basic structure of these crystals, three-, four-, and six-membered rings formed by WO6 octahedra. Microcluster models in which the atomic arrangement was similar to that of hexagonal WO3 were assumed and investigated in detail. The pair distribution functions calculated from these models showed good agreement with the observed values, and the structure of a-WO3 films was consequently suggested to consist of clusters in which the octahedra were arranged in the same manner as those in hexagonal WO3. © 1989.

DOI： 10.1016/0022-4596(89)90180-1

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The heavy metal oxide (HMO) glasses in the ternary Bi2O3-WO3-TeO2 system were prepared to investigate the Er3+ amplification properties. The present HMO glasses showed larger and broader Er3+ emission spectra as compared with the conventional silica-based glasses. Dominant factors on the emission intensity and bandwidth were explored on the basis of theories. The emission intensity was successfully explained by the theoretical radiative decay rate, and it was also confirmed that the refractive index was predominant on the emission intensity. A Judd-Ofelt Omega(6) parameter was also examined, and its influence on the bandwidth was not recognized. Other factors, such as O1s binding energy and structural variation around Er3+ ions, were estimated, and their effects on the bandwidth were however not clarified. The unique chemical bonding character in the HMO glasses might be responsible for the spectral broadening.

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Refining behavior of the Ph-substituted Bi-2223 phase through mechanical grinding and thermal behavior of its ground powder on heating in air have been examined for samples with a nominal composition of Bi1.8Pb0.4Sr2Ca2Cu3.2Oz by XRD, DTA, SEM, TEM, ED and magnetic measurements. The 2223 phase easily changes into superfine powder by mechanical grinding. On annealing the ground powder below 800 degrees C, various second phases were formed, while at 850 degrees C the 2223 phase was reformed depending upon the amount of the superfine powder in the samples.

DOI： 10.1016/0921-4534(94)91462-1

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Mechanical grinding and reforming process of the Pb-substituted 2223 phase has been studied for the monophasic samples with a composition of Bi_0.9Pb_0.2SrCaCu_1.6O_Z. The 2223 phase changes to ultla-fine powder by full grinding, exhibiting no magnetic response, while the ultra-fine powder and the small 2223 crystals coexist in samples ground for short periods. Some second phases were formed in the ground powder subjected to heating at temperatures between 500°C and 800°C. On the other hand, annealing of the bulk samples below 800°C leads to precipitation of the 3321 phase identified as Sr_2.5Bi_0.5Pb₃Ca₂CuO_Z. Precipitation of second phases in the coexistent powder was interpreted by those in ultra-fine powder and bulk samples.

DOI： 10.2497/jjspm.41.396

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Pining characteristics due to the precipitates of the "3321"(Sr_2.5Bi_0.5Pb₃Ca₂CuO_z) phase have been studied in the Bi-2223 phase in the Bi-Pb-Sr-Ca-Cu-O system by mainly XRD and magnetic measurements. The precipitation of the "3321" phase was controlled by changing annealing temperature and annealing time in air. On annealing at 750°C for 10min and 1h, the larger hysteresis loops in M-H curves were observed in comparison with the initial one before annealing. However, the hysteresis loops became smaller with increasing precipitation of the "3321 " phase. Furthermore, the 2223 phase annealed at 400°C and 500°C, in which no precipitation of the "3321 " phase was observed, exhibits larger hysteresis loops.

DOI： 10.2497/jjspm.41.1501

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Thermal behavior of the Bi-2223 phase in the Bi, Pb-Sr-Ca-Cu-O system, especially segregation and dissolution reaction of the "3321" phase which was identified as Sr_2.5Bi_0.5Pb₃Ca₂CuO₂, has been studied by XRD, SQUID and resistivity measurements. On annealing below 830°C in air, the "3321" phase precipitated from the 2223 crystals. When the 2223 phase was annealed at 750°C in O₂stream, the precipitation of the "3321 " phase increased. On annealing at 750°C in Ar stream, however, no precipitation of the "3321" phase was detected. By reheateing at 850°C even for 1min, the "3321" phase was almost dissolved into the mother 2223 crystals. When the 2223 phase was reheated at 750°C in Ar stream after annealing at 750°C in air, the "3321 " phase disappeared. On the contrary, the "3321" phase was stable on reheating at 870°C in O₂ stream. Therefore, it seems that the "3321" and the 2223 phase coexist in epuilibrium in a high oxygen partial pressure.

DOI： 10.2497/jjspm.41.388

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Refining behavior due to a small mechanical force and re-formation process of the 2223 phase on heating have been examined for the samples with a nominal composition of Bi_1.8Pb_0.4Sr₂Ca₂Cu_3.2O_z by XRD, TEM, ED, AFM and TG-DTA. The 2223 phase is brittle and easily cleaved at Bi-O double layers in its crystals by a small mechanical force, resulting in changing into the superfine powder with a thickness of 1/2c. On heating the ground powder at 500°C to 800°C in air, various phases were formed from the superfine powder.

DOI： 10.2497/jjspm.41.1497

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Chemical and mechanical stability of the Ba-added high-Tc phase has been studied using XRD and DTA for samples of Bi_0.9Pb_0.2Sr_1.0Ba_xCa_1.0Cu_1.6O_z with x=0 and 0.05. Some impurities were observed in all samples after the heat treatment at 300-820°C. BaPb_0.75Bi_0.25O₃ was also formed in the Ba-added samples heated at 700-800°C. These impurities were thought to be formed from the amorphous phase which was produced by mechanical grinding of the high-Tc phase. The impurities disappeared and an almost monophasic sample of the high-Tc phase was obtained by heating at 850°C. The lattice parameter c of the Ba-added high-Tc phase was longer than that of the Ba-free one above 800°C. The parameter c of the Ba-added sample heated at 850°C increased with an increase of heating time and was saturated over 48h. The increase of c was due to the Ba dissolution in the high-Tc phase.

DOI： 10.2497/jjspm.40.204

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The effect of Li addition to the low-Tc phase in Bi-Sr-Ca-Cu-O system has been studied for the samples with nominal compositions of Bi:Sr:Ca:Cu:Li=2:3-y:y:2:x(x=0 to 0.6, y=1.25, 1.5, 2.0) heated at 600 to 760°C for 12 to 48h in air. The Li addition promotes the formation of the low-Tc phase. Monophasic samples of the low-Tc phase were obtained for x=0.2 to 0.6 by heating at remarkably lower temperatures. The lattice constant c of the low-Tc phase depends on y as well as Li content. As the heating time extends, the Li content in the low-Tc phase decreases. For y=1.25 and 1.5 c increases as the Li content increases. On the contrary, c for y=2.0 decreases as the Li content increases.

DOI： 10.2497/jjspm.40.196

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Phases and their relations in the BiO1.5-SrO(SrCO3)-CuO system have been studied mainly by XRD. The crystal structure of the newly found phase has been examined by XRD, TEM and ED. Phase equilibrium was established at 720°C in air. Monophasic products of the newly found phase were obtained at 720°C for a composition of Bi:Sr:Cu=0.25:0.55:0.20. The newly found phase has a tetragonal structure with lattice parameters of a=5.513Å and c=39.93Å. © 1993, Japan Society of Powder and Powder Metallurgy. All rights reserved.

DOI： 10.2497/jjspm.40.1049

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Chemical and mechanical stability of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system has been studied. In particular, the formation of the high-Tc phase has been discussed for samples of the amorphous powder with a composition of Bi0.9Ph0.2Sr1.0Ca1.0Cu1.6Oz prepared by mechanical grinding. Annealing of the amorphous powder at low temperatures(500-800°C) leads to precipitation of some impurity phases. The Pb-rich low-Tc phase with an orthorhombic structure symmetry was found to form in samples of the amorphous powder heated at 820°C in air. The formation of the Pb-rich low-Tc phase seems to suppress the formation of the high-Tc phase in subsequent heat treatments at 850°C. Almost monophasic products of the high-Tc phase were obtained when the amorphous powder was heated at 840°C for 48h and subsequently at 850°C for 96h after calcination at 720°C. © 1993, Japan Society of Powder and Powder Metallurgy. All rights reserved.

DOI： 10.2497/jjspm.40.187

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Chemical stability of the Bi-2223 phase has been studied for the samples Bi_0.9Pb_0.2SrCaCu_1.6O₂ Annealing of the bulk samples below 800°C leads to precipitation of the 3321 phase identified as Sr_2.5Bi_0.5Pb₃Ca₂CuO_z. The precipitation of the 3321 phase from the 2223 phase decreases the volume fraction of the 2223 phase but Tc (x) remains unchanged. It was found by XRD and SQUID measurements and SEM observation that, through reheating at 850°C after heating at 750°C, the 3321 phase disappeares and the volume fraction of the 2223 phase perfectly recovers.

DOI： 10.2497/jjspm.40.1057

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(111)- and (100)-oriented Fe₃O₄ films were epitaxially formed on a-A1₂O₃(0001) and MgO(100) single-crystalline substrates, respectively, by reactive evaporation method. The formation ranges of the epitaxial Fe₃0₄ films were determined as a function of substrate temperature, oxygen partial pressure, and a deposition rate. Their crystalline qualities were examined by various methods such as X-ray diffraction, RHEED and resistivity mesurements. A lattice mismatch of about 0.3% between Fe₃O₄ and MgO was very small. Then the film deposited on MgO seemed to have a good crystallinity and a smooth surface. Moreover the Verwey transition was clearly detected by a resistivity mesurement at about 110K. The transition temperature was nearly consistent with that of the bulk, indicating a good stoichiornetry of the sample film.

DOI： 10.2497/jjspm.39.981

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Chemical and mechanical stability of the high-Tc phase has been studied for the samples of Bi_0.9Pb_0.2Sr_1.0Ca_1.0Cu_1.6O_x. Mechanical grinding converts the high-Tc phase into a nonsuperconducting amorphous phase. The ground high-Tc phase is not stabilized on annealing at lower temperatures below 820°C. Annealing at lower temperature leads to precipitation of some impurity phases and the low-Tc phase which depends on annealing temperature and time. The high-Tc phase is recovered by annealing at 850°C. The lattice parameters a and c of the high-Tc phase annealed at 850°C are longer than those below 820°C.

DOI： 10.2497/jjspm.39.779

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The effect of Li-addition to the low-Tc phase in Bi-Sr-Ca-Cu-O system have been studied for the samples with nominal compositions of Bi:Sr:Ca:Cu:Li=2:1.5:1.5:2-x:x heated at 720 to 845°C for 12 to 24h in air (x=0 to 0.8). The Li-addition promotes the formation of the low-Tc phase. Single phase of the low-Tc phase was obtained for the sample with x=0.2 to 0.4 more easily than the sample with x=0. The lattice constant c of the low-Tc phase increases as the Li content increases. As the heating period becomes longer, the amount of Li content in the low-Tc phase decreases.

DOI： 10.2497/jjspm.39.763

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Language：English   Publisher：Faculty of Engineering, Okayama University  

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DOI： 10.2497/jjspm.39.985

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The effects of cooling condition and Ba addition time on Tc of high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system were studied. X-ray diffraction and DC resistance measurements were carried out to observe phase identification and Tc values for a series of samples with compositions of Bi:Pb:Sr:Ba:Ca:Cu=0.9:0.2:1.0:X:1.0:1.6(X=0-0.05). When a mixture of BaCO₃ and synthesized high-Tc phase was heated at 850°C for 60h in air, only a solid solution of high-Tc phase was formed in a quenched sample. However, in a sample cooled down slowly, Bi₃(Sr, Ba)₄Ca₃O_z was found as an impurity phase in addition to the solid solution of high-Tc phase. Mixtures of BaCO₃ (X=0.04) and the rest of metal oxides or metal carbonates were heated at 845°C 96h in air. Bi₃(Sr, Ba)₄Ca₃O_z was also found in addition to the high-Tc phase in a quenched sample. When BaCO₃ was added to the synthesized high-Tc phase, Tc(R=0) was 119K for the heated samples. When BaCO₃ was added in starting materials, Tc decreased to 110K due to the formation of Bi₃(Sr, Ba)₄Ca₃O_Z.

DOI： 10.2497/jjspm.39.374

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The effects of Ba addition and grinding time on Tc of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system have been studied. Samples with compositions of Bi:Pb:Sr:Ba:Ca:Cu=0.9:0.2:1.0:X:1.0:1.6(X=0-0.05) were prepared by grinding the high-Tc phase and BaCO₃ powders for various periods (20 to 120min). The high-Tc phase degraded with grinding time. In samples of a composition of X=0.05 heated at 845≥C for 60h in air, a small amount of the low-Tc phase and Bi₃(Sr, Ba)₄Ca₃O_z besides the high-Tc phase were formed. The heating led to the grain growth of the high- Tc phase with increasing grinding time. However, Tc(R=0) was decreased due to the formation of the low-Tc phase and Bi₃(Sr, Ba)₄Ca₃O_z.<BR>In a sample with X=0.05 heated at 850°C for 60h in air, only a solid solution of the high-Tc phase was formed. Tc(R=O)=125K was attained in this sample. The Meissner diamagnetic response at 125K was confirmed by SQUID, but the volume fraction of the 125K phase was estimated below 1%.

DOI： 10.2497/jjspm.39.771

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The effects of Ba-addition to the high-Tc phase in the Bi-Pb-Sr-Ca-Cu system have been studied for the samples with a starting composition of Bi:Pb:Sr:Ba:Ca:Cu=0.9:0.2:1.0:x: 1.0:1.6 heated at 850°C in air (x=0 to 0.10). Various amounts of BaCO3 were added to the high-Tc phase with a composition of Bi:Pb:Sr:Ca:Cu=0.9:0.2:1.0:1.0:1.6. Ba-addition raises Tc
Tc(R~0)=122K and Tc(R=0)=120K for the sample with x=0.05 heated at 850°C for 60h. XRD and ICP analyses indicate that the high-Tc phase contains Ba of x≦0.05 as a solid solution. © 1991, Japan Society of Powder and Powder Metallurgy. All rights reserved.

DOI： 10.2497/jjspm.38.1039

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