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

Structural analyses of niobium oxide (NbO_x) amorphous film prepared with a sputtering method have been performed by using synchrotron X-ray radiation at SPring-8. The composition was determined as Nb₂O₅·0.8H₂O from the measurements of Rutherford back scattering, X-ray fluorescence, X-ray absorption near edge structure, and thermal desorption spectroscopy. Structural information was obtained by extended X-ray absorption fine structure and high energy X-ray diffraction measurements. It was supposed from the experimental data that NbO_x consisted of distorted NbO_n polyhedra connected by corner- and edge-sharing. Structural models were constructed with reverse Monte Carlo (RMC) simulations. In the RMC models, the structural characteristics were successfully reproduced, and H atoms were, however, randomly distributed. Then, bond valence sum (BVS) constraint was introduced to the RMC simulation. As the results, narrower distribution in BVS was achieved for all the constituent atoms, and distinct OH bonds were effectively generated in the RMC model.

DOI： 10.2109/jcersj2.17053

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

Electronic structure of amorphous niobium oxide prepared by a sputtering method was investigated based on optical absorption and photoelectron spectroscopies. In the valence band photoelectron spectra, broad peaks without any characteristic components were observed. Then, theoretical calculations based on a density functional theory were performed to interpret the experimental spectra by using three Nb₂O₅ polymorphs. Among the polymorphs, M-phase with tetragonal structure showed better reproducibility than the other B- and R-phases with monoclinic structure. It was finally concluded that the amorphous niobium oxide had a similar electronic structure to M-Nb₂O₅, and it was supposed that the broad feature in the photoelectron spectra was due to the broad distribution of Nb–O bonds in NbO₆ polyhedra, which was characteristic in M-Nb₂O₅.

DOI： 10.2109/jcersj2.16180

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DOI： 10.1016/j.pnucene.2016.05.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WALTER DE GRUYTER GMBH  

With the advent of third-generation synchrotron sources and the development of light source techniques, X-ray scattering techniques have become feasible, leading to new approaches for studying the structures of disordered materials in a quantitative manner. We introduce a dedicated diffractometer for high-energy total X-ray scattering measurement and a newly developed anomalous X-ray spectrometer at SPring-8. As advanced methodologies for the measurement of liquids, we now offer three state-of-art levitation instruments for aerodynamic levitation, electrostatic levitation, and acoustic levitation at the SPring-8 beamlines, covering a wide temperature range of -40-3000 degrees C. Furthermore, scientific investigations of glasses, liquids, and amorphous materials reported in the last five years at SPring-8 are reviewed.

DOI： 10.1515/zpch-2015-0654

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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Ceramic Society of Japan and the Korean Ceramic Society  

DOI： 10.1016/j.jascer.2013.03.003

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ceramic Society of Japan  

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

Behavior of phosphorus associated with phase separation and the effect of TiO2 addition on the phosphorus distribution were investigated in Na2O-B2O3-SiO2 ternary glass system. After heat treatment, phase separation by spinodal decomposition was commonly observed. In the phase separation of TiO2-free glasses, phosphorus was preferentially distributed into B2O3-rich phase, and after TiO2 addition, phosphorus distribution into SiO 2-rich phase was also observed. With increasing TiO2 content, the amount of phosphorus distributed into SiO2-rich phases increased up to 90%. 31P MAS NMR indicated that phosphorus in the glasses was mainly present in negatively-charged Q2 units with terminal oxygen atoms, and in the TiO2-containing glasses, Q 1 or Q0 units containing P-O-Ti bond were confirmed. Despite the formation of negatively-charged Q1 or Q0 units, phosphorus was distributed into SiO2-rich phase, which was due to the distribution of Ti4+ ions with higher coordination numbers acting as network modifiers.

DOI： 10.1002/9781118472590.ch16

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

Planar waveguides were prepared on 12Na2O·10NbO 2.5·25WO3·53TeO2·1Er 2O3 ([NbWEr]) substrate glass by Ag+-Na + ion-exchange using a dry electromigration process. The optical properties of the waveguides were characterized and compared with those of [NbWEr] glass waveguides prepared by Ag+-Na+ ion-exchange by thermal diffusion. After ion-exchange by both a dry electromigration process and thermal diffusion, the transmittance of the glasses slightly decreased from that of the [NbWEr] substrate glass but frosting was not observed on these ion-exchanged glasses. The depth of the waveguide fabricated at 300°C by a dry electromigration process was about 8 μm and deeper than that at 380°C by thermal diffusion. On the [NbWEr] glass ion-exchanged at 300°C by a dry electromigration process, the stains seen in the [NbWEr] glass ion-exchanged at 380°C by thermal diffusion were hardly observed. Therefore, the dry electromigration process is promising due to the reduction of the process temperature and fewer stains.

DOI： 10.1002/9781118472590.ch24

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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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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 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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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：ELSEVIER SCIENCE BV  

A glass of Li2O-Nb2O5-SiO2-B2O3 with an addition of CuO or Sm2O3 crystallizing in nonlinear optical lithium niobate LiNbO3 is developed. Crystalline lines of Lithium Niobate have been fabricated by continuous wave laser irradiation of the glass surface. The crystalline laser written lines have been found, by means of micro-Raman and Second Harmonic experiments, to be well oriented with its c-axis pointing along the laser scanning direction. The analysis of the confocal micro luminescence spectra obtained at the crystalline line have confirmed the incorporation of rare-earth ions in the crystalline network. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2008.04.015

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Crystal lines consisting of nonlinear optical fresnoite-type Ba2TiX2O8 (X = Si, Ge) crystals are patterned on the surface of CuO (1 mol%)-doped 33.3BaO-16.7TiO(2)- 50SiO(2) or -50GeO(2) glasses by continuous-wave (cw) neodymium:yttrium aluminum garnet (Nd:YAG) laser (wavelength 1064 nm) irradiation. It is confirmed from polarized micro-Raman scattering spectra that the c axis of Ba2TiX2O8 crystals in the lines are oriented along the laser-scanning direction (i.e., parallel to the lines). The azimuthal dependences of second-harmonic (SH) intensities for the crystal lines indicate unique fringe patterns, and the c-axis orientation of the crystals is supported from the analyses of fringe patterns. The value of the d(31)/d(33) ratio is found to be similar to 23 for Ba2TiSi2O8 (BTS) crystal lines, and similar to 13 for Ba2TiGe2O8 (BTG) crystal lines, where d(31) and d(33) are the principal d tensors for the second-order optical nonlinearity of fresnoite-type crystals.

DOI： 10.1557/JMR.2008.0135

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DOI： 10.1016/j.jnoncrysol.2007.07.081

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

In the crystallization process of 30BaO-15TiO(2)-55GeO(2) (BTG55), we demonstrated by an x-ray diffraction analysis that a stepwise heat treatment enables a selective crystallization of fresnoite and benitoite, two crystalline phases obtained from the BTG55 mother glass and that these two phases form a dual surface layer. The result indicates that the stepwise heat treatment generates a compositional heterogeneity inside the glass matrix, which facilitates the nucleation of the fresnoite phase. The mechanism for the generation of the dual surface layer is discussed. Due to a marked difference in optical nonlinearity of the two phases, the selective crystallization may open the possibility of an optimized heat-treatment condition to achieve a large optical nonlinearity in crystallized glass. Also, two types of fresnoite, tetragonal and orthorhombic, were observed in the crystallized phase after a stepwise heat treatment of 690/720 degrees C. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2743827

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

Glass fibers with a diameter of similar to 100 mu m are drawn by just pulling up melts of 40BaO center dot 20TiO(2)center dot 40SiO(2) glass, and transparent crystallized glass fibers consisting of nonlinear optical fresnoite Ba2TiSi2O8 nanocrystals (particle size: similar to 100-200 nm) are fabricated by crystallization of glass fibers. Precursor glass fibers and nanocrystallized glass fibers are etched chemically using a meniscus method, in which an etching solution of 0.1 wt%-HF/hexane is used. Glass fibers with sharpened tips (e.g., the taper length is similar to L = 200,mu m and the tip angle is similar to theta = 23 degrees) are obtained. It is found that etched nanocrystallized glass fibers also have sharpened tips (L = 50 mu m, theta = 80 degrees). Compared with precursor glass fibers, nanocrystallized glass fibers show a high resistance against chemical etching in a 0.1 wt%HF solution. Although sharpened tips in nanocrystallized glass fibers do not have nanoscaled apertures, the present study suggests that nanocrystallized glass fibers showing second harmonic generations would have a potential for fiber-type light control optical devices.

DOI： 10.2109/jcersj.115.374

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This paper reports recent progress in the patterning of non-linear optical crystals on the glass surface by laser irradiation. Two techniques for the writing of crystal lines have been developed, i.e., rare-earth (samarium) atom heat processing and transition metal atom heat processing, in which a continuous wave Nd:YAG laser (wavelength: lambda=1064 nm) is irradiated to the glasses containing rare-earth (RE: Sm3+, Dy3+) ions or transition metal (TM: Ni2+, Fe2+, V4+) ions. The writing of crystal lines such as beta-BaB2O4, SmxBi1-xBO3, and Ba2TiGe2O8 showing second harmonic generations has been successful. It is clarified from the azimuthal dependence of second harmonic intensity and polarized micro-Raman scattering spectra that crystal lines consist of highly oriented crystals along the crystal line growth direction. It is also possible to write two-dimensional crystal bending or curved lines by just changing the laser scanning direction. The mechanism of the laser-induced crystallization has been proposed.

DOI： 10.1111/j.1551-2916.2006.01441.x

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The correlation between heat-treatment temperature for crystallization and orientation of surface crystalline phase, which should correspond to the intensity of second-order optical nonlinear susceptibility, in 30BaO-15TiO(2)-55GeO(2) (BTG55) crystallized glass was examined by measurements of x-ray diffraction (XRD) and second harmonic generation. A highly oriented fresnoite (Ba2TiGe2O8) or benitoite (BaTiGe3O9) phase was found to nucleate from the same mother BTG55 glass depending on the heat-treatment temperature, and both the fresnoite and benitoite phases showed XRD patterns of surface crystallization. It was found that the crystallization behavior of the two phases was strongly affected by the heat-treatment temperature. Based on this finding, the nonlinear optical property has also been tailored using the heat-treatment procedures. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2433992

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

A technique for the patterning of ferroelectric crystal lines such as Sr(0.5)Ba(0.5)Nb(2)O(6), LiNbO(3), beta'-Gd(2)(MoO(4))(3) at the glass surface has been developed, i.e., transition metal atom heat processing, in which continuous wave lasers such as Nd:YAG (wavelength: lambda=1064 nm) are irradiated to the glasses containing transition metal (TM: Cu(2+), Ni(2+)) ions. The absorbed laser results in local heating of glass, consequently inducting crystallization. By scanning laser (power: < 1W) at constant speeds such as 10 mu m/s, ferroelectric crystal lines are written successfully at the glass surface. The surface morphology and orientation of crystals in the lines are clarified from confocal laser microscope observations and polarized micro-Raman scattering spectra measurements. In some glasses, the patterning of crystal lines consisting of oriented ferroelectrics is possible.

DOI： 10.1109/ISAF.2007.4393245

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Language：English   Publisher：American Institute of Physics  

DOI： 10.1063/1.2210173

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Language：English   Publisher：American Institute of Physics  

DOI： 10.1063/1.2212272

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

We report on a novel technique for formation of nano-particle structures in KNbO3-TeO2, glasses induced by ultraviolet (UV) XeCl excimer laser irradiations operating at 308 nm wavelength. The glasses with a composition of 0.5Er(2)O(3)-15K(2)O-15Nb(2)O(5)-70TeO(2) (mol%), which are known to exhibit a nano-crystallization behavior by heat treatments, have been used in this experiment. It has been found that the morphological properties of nanoparticles, such as diameter, height, and distribution density of nano-particles, can be tailored by the pulsed UV laser conditions. The nature of these nano-structures on glass surface induced by laser processing has been clarified that laser-induced nano-particles are consisting of the same composition as that in glass substrate.

DOI： 10.2109/jcersj.114.293

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications  

A high magnetic field of H = 10 T was applied to 30BaO-15TiO 2-55GeO2 glass through its crystallization process. It was found that the c-axis of Ba2TiGe2O8 optical nonlinear/ferroelectric crystals oriented along the magnetic field. The second harmonic intensity of crystallized glass which the high magnetic field was applied perpendicular to the surface of glass was enhanced compared with a conventional crystallization in no magnetic field. Transparencies, photorefractive indices and thicknesses were also measured. As a result, crystal orientation of Ba2TiGe2O8 in glass matrix induced by a high magnetic field causes improvement of transparency and low value of photorefractive index.

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Two-dimensional crystal curved lines consisting of the nonlinear optical SmxBi1-xBO3 phase are fabricated at the surface of 8Sm2O3·37Bi2O3· 55B2O3 glass by continuous wave Nd:YAG laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) with a power of ∼0.9 W and a laser scanning speed of 5 μm/s. The curved lines with bending angles of 0-90° or with sine-shapes are written by just changing the laser scanning direction. The polarized micro-Raman scattering spectra for the line after bending are the same as those for the line before bending, indicating that the crystal plane of SmxBi1-xBO3 crystals to the crystal growth direction might be maintained even after the change in the laser scanning direction. It is found from laser scanning microscope observations that the crystal lines at the surface are swelled out smoothly, giving a height of about 10 μm. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2005.08.004

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Language：English   Publisher：The Ceramic Society of Japan  

In this study, we examined the temperature dependence of the second-harmonic (SH) intensity and Raman shift in the langasite-type Ba_3Ga_2Ge_4O_<14> (BGG) and Na_2CaGe_6O_<14> (NCG) crystalline phases. The SH intensity curves revealed an anomalous temperature behavior around 370℃ and 270℃ in the BGG and NCG phases, respectively. Furthermore, as a result from the Raman spectral measurement, it was suggested that the anomaly observed in the lagasite-type phases originated in the A-site.

DOI： 10.2109/jcersj.113.692

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Language：English   Publisher：INSTITUTE OF PURE AND APPLIED PHYSICS  

Crystallization of the langasite-type La3Ga5GeO14–Ba3Ga2Ge4O14 mixed crystals in the stoichiometric corresponding glasses was studied by differential thermal and X-ray diffraction analyses, and by Raman spectroscopy. Although the glasses used in this study were multicomponent systems (BaO–La2O3–Ga2O3–GeO2), the langasite-type phases were singly crystallized in the corresponding glasses. The Raman spectroscopic study revealed the structural similarity on the scale of short-range order between the langasite-type phase and the corresponding glasses. This also strongly suggested the coexistence of Ga and Ge with six-coordination in the gallogermanate glasses.

DOI： 10.1143/JJAP.44.7177

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Language：English   Publisher：The Ceramic Society of Japan  

Nanocrystallized glasses with the composition of 40BaO・20TiO_2・40SiO_2, stoichiometric to fresnoite (Ba_2TiSi_2O_8), have been prepared by heat-treatment at various temperatures, and their optical properties, second-harmonic generation (SHG) and photoluminescence (PL), have been examined. The glass subjected to the heat-treatment at 760℃ for 1h showed a dense formation of Ba_2TiSi_2O_8 crystals with the dimension of 200-300nm, and maintained a visual transparency. Visible green light corresponding to SHG at 532nm was confirmed in the transparent Ba_2TiSi_2O_8 nanocrystallized glasses. The maximum second-harmonic intensity in the nanocrystallized samples was on the order of 1/100 when compared to that of an α-quartz single crystal. Furthermore, the bluish white PL with a peak at the wavelength of about 470nm was also visually observed in samples heat-treated at 750-800℃.

DOI： 10.2109/jcersj.113.419

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DOI： 10.1111/j.1551-2916.2005.00166.x

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

Second order nonlinear optic behavior of a transparent glass-ceramic containing borate crystallites in tellurite glass is reported. Controlled heat-treatment resulted in surface crystallization of BaB4O7 in the BaO-B2O3-TeO2 glass system.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Optical Society of America (OSA)  

Transparent nano-crystallization in glass must be the best material solution to obtain a novel functional glass with permanent second-order optical nonlinearity. Challenges for laser-induced formation of photonic circuits from nano-particles ordering to single-crystal patterning in glasses are presented. © 2005 Optical Society of America.

DOI： 10.1364/fio.2005.pdp_b1

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DOI： 10.1111/j.1151-2916.2002.tb00065.x

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DOI： 10.1063/1.1808873

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Nonlinear optical β-BaB2O4 (β-BBO) crystal straight lines are written in 10Sm2O 3·40BaO·50B2O3 glass by irradiation of a continuous wave Nd:YAG laser operating at 1064 nm. The linearly polarized micro-Raman scattering spectra for β-BBO crystal lines are consistent with those for commercially available y-cut β-BBO bulk single-crystals, supporting that β-BBO crystal straight lines with the c-axis orientation along the YAG laser scanning direction might be single-crystals. The photoluminescence spectra with large intensities and Stark splitting are observed for β-BBO crystal lines, and it is concluded that some amounts of Sm3+ ions in the glass are incorporated into β-BBO crystal lines. Two-dimensional β-BBO crystal curved lines with a bending angle of 30° are successfully written in 10Sm2O 3·42BaO·48B2O3 glass. © 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2004.04.010

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Language：English   Publisher：The Ceramic Society of Japan  

Second-order optical nonlinearities for the langasite-type phases obtained by crystallization of corresponding glasses are clarified for the first time. It is confirmed that most of langasite-type crystalline phases can be formed by crystallization in the corresponding glasses without introducting of any impurity phases, e.g., the glasses with the stoichiometric composition of Ba_3Ga_2Ge_4O_<14>, BaGa_4La_2Ge_2O_<14>, Pb_3Ga_2Ge_4O_<14>, etc. We find that Pb_3Ga_2Ge_4O_<14> and Pb_3AlGaGe_4O_<14> phases exhibited strong second-harmonic intensities of approximately 100 times as large as α-quartz by means of a powder technique, demonstrating that those langasite-type crystals are excellent nonlinear optical materials. It is also suggested that the octahedral site is one of keys for second-order optical nonlinearity in langasite-type crystals.

DOI： 10.2109/jcersj.112.61

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

Some K2O-Nb2O5-GeO2 glasses are prepared, and their crystallization behaviors are examined. 25K(2)O.25Nb(2)O(5).50GeO(2) glass with the glass transition temperature T-g = 622degreesC and crystallization onset temperature T-x = 668degreesC shows a prominent nanocrystallization. The crystalline phase is K3.8Nb5Ge3O20.4 with an orthorhombic structure. The sizes of crystals in the crystallized glasses heat-treated at 630degrees and 720degreesC for 1 h are similar to10 and 20-30 nm, respectively, and the crystallized glasses obtained by heat treatments at 620degrees-850degreesC for 1 h maintain good transparency. The density of crystallized glasses increases gradually with increasing heat-treatment temperature, and the volume fraction of crystals in the sample heat-treated at 630degreesC for 1 h is estimated to be similar to35%. The usual Vickers hardness and Martens hardness (estimated by nanoindentation) of 25K(2)O.25Nb(2)O(5).50GeO(2) glass change steeply by heat treatment at T-g, i.e., at around 35% volume fraction of nanocrystals. The present study demonstrates that the composite of nanocrystals and the glassy phase has a strong resistance against deformation during Vickers indenter loading in crystallized glasses.

DOI： 10.1111/j.1551-2916.2004.00113.x

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Challenges for laser-induced structure ordering from nano-particles to single-crystal patterning in glasses are described. Transparent crystallization in glass must be the best material solution to obtain novel functional glasses with a permanent second-order optical nonlinearity. We focus on the new functions created by structure ordering in glass by means of laser micro-fabrication for space-selected crystallization. Two topics in our recent experimental results of laser-induced structure ordering in glass will be presented as follows: 1) UV-laser induced structure ordering of nano-particles in tellurite-based glasses and possible photonic integrated circuits with innovative minute scale. 2) Single crystalline patterning by atom heat laser processing in Sm-doped glasses for optical waveguides with second-order nonlinearity.

DOI： 10.1117/12.595719

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

The origin, and properties of second-harmonic generation (SHG) from crystalline particles and their crystalline phases in GeO2-SiO2 glass films were investigated. GeO2-SiO2 glass films with a thickness of approximately 5 pin were fabricated by the chemical vapor-phase deposition (CVD) method. Heat treatments in the temperature range of 1100-1260degreesC for durations of 2-8 h have been performed to crystallize the glass films. X-ray diffraction (XRD) peaks at around 2theta = 22degrees in the crystallized GeO2-SiO2 films were observed, and the obtained XRD patterns in the glass films are exactly the same as those in ultraviolet (UV) poled GeO2-SiO2 glasses with a large second-order, optical nonlinearity comparable to that in LiNbO3 crystals. Using a SHG microscopic technique, it has been found that the intensity of SHG emission from crystalline particles is clearly dependent on stress-induced optical retardation which is accompanied by the formation of crystalline particles of the pseudo-beta-cristobalite containing GeO2. In addition, a new technique for enhancing the intrinsic SHG by means of modification of defect states is demonstrated.

DOI： 10.1143/JJAP.42.7326

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DOI： 10.1063/1.1615833

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEE-INST ELEC ENG  

A large change of refractive index, An, induced by ultraviolet excimer laser irradiations in Er2O3-doped tellurite-based glass, which is a promising material for fibre amplifiers, has been obtained. The value of Deltan/n larger than 5% was successfully achieved, and amplitude of Deltan depending on Er2O3-concentrations has been found.

DOI： 10.1049/el:20031031

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

KNbGeO5 (i.e., 25K(2)O-25Nb(2)O(5)-50GeO(2)) glass with the glass transition 622 degreesC and crystallization onset 668 degreesC temperatures shows prominent nanocrystallization, giving K3.8Nb5Ge3O20.4 nanocrystals with the size of similar to30 nm. Dielectric, elastic and mechanical properties of transparent nanocrystallized KNbGeO5 glasses are examined using some techniques such as polarizability analysis, cube resonance spectra and Vickers nanoindentation. Electronic polarizability, shear modulus, bulk modulus, Young's modulus (E), Debye temperature (theta(D)), Vickers hardness, and deformation energies during nanoindentation increase largely due to the nanocrystallization, e.g., E=64.1 GPa and theta(D)=500 K for the base glass and E=85.5 GPa and theta(D)=575 K for a transparent nanocrystallized glass. The values of Poisson's ratio and fractal bond connectivity of nanocrystallized glasses are the same as those of the base glass, suggesting that relative arrangements of constituent ions (K+, Nb5+, Ge4+) in nanocrystallized glasses are basically similar to those in the base glass. The present study suggests that nanocrystallization in glass results in not only more compact atomic arrangements but also in an increase in interatomic strength. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1609641

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Publisher：Elsevier  

DOI： 10.1016/S0022-3093(03)00365-X

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A continuous-wave (CW) YAG laser (power: 0.75-0.9 J/s, irradiation time: 15 s-15 min) with a wavelength of 1064 nm is irradiated to 11.1Sm(2)O(3).44.4BaO.44.4B(2)O(3) glass, and the formation of beta-BaB2O4 (beta-BBO) crystalline dots with a diameter of 30-150 mum is confirmed from micro-Raman spectra. beta-BBO crystals with around 200 mum length grow towards the interior of the glass. The incorporation of Sm3+ into beta-BBO crystalline dots is suggested from micro-Raman and fluorescence spectra. The second harmonic generation is detected from the array (10 x 10 = 100 dots) of beta-BBO crystalline dots, indicating that each crystalline dot formed by YAG laser irradiation is a nonlinear optical crystal. CW YAG laser irradiation to glass with Sm3+ ions is a nice technique for a spatially controlled crystal growth. (C) 2003 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(03)00047-7

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

The authors report what is, to our best knowledge, the first observation of second-harmonic generation (SHG) directly from the crystalline particles in Ge-doped SiO2 (Ge:SiO2) glass films. Ge:SiO2 glass films with approximately 5 mum thickness were fabricated by chemical vapor-phase deposition. X-ray diffraction ( XRD) peaks at around 2theta=22degrees in thermally crystallized Ge:SiO2 films were observed, and obtained XRD patterns are exactly the same as those in ultraviolet-laser-poled Ge: SiO2 glasses. Using SHG microscopic technique with a Nd:YAG laser, it has been successfully found that SH emitting with 532 nm wavelength is observed directly from the crystalline particles induced in the crystallized films. (C) 2003 Optical Society of America.

DOI： 10.1364/OE.11.001598

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DOI： 10.1016/S0022-4596(03)00026-4

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DOI： 10.1016/S0925-3467(02)00242-2

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

A transparent TeO2-based nanocrystallized (crystalline particle size: similar to40 nm) glass (composition: 15K(2)O . 15Nb(2)O(5). 68TeO(2) . 2MoO(3)) showing a second harmonic generation (SHG) has been prepared, and a thermal poling has been applied to examine whether a poling technique is effective in enhancing the SH intensity of nanocrystallized glass. In the poling condition of 2.0 kV (DC voltage), 210 degreesC and 40 min, the SH intensity of nanocrystallized glass is enhanced, demonstrating that a combination of nanocrystallization and thermal poling is an useful technique to induce a SHG in glass. As similar to the case of glass, a prominent SHG is observed at the anode side in the thermal poling, suggesting the increase in polarization in nanocrystals. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0030-4018(02)02356-8

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DOI： 10.1016/S0022-3093(02)01638-1

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We propose and demonstrate gratings and two-dimensional (2D) photonic structure of nanometer-scale crystals/particles in glass surface created by one of the most simple way ever reported. Grating structures consisting of nanocrystals have been fabricated on surface of tellurite-based glasses, with a composition of 15K(2)O-15Nb(2)O(5)-70TeO(2) (mol%), using photoinduced nano-crystallization. A conventional phase mask technique was performed for the grating fabrication with a XeCl excimer laser operating at 308 nm. Periodic structure with 400 nm pitch constructed by lines of regularly ordered nanoparticles having a diameter up to about 100 nm was confirmed by atomic force microscopy and scanning electron microscopy. It is strongly suggested from measurement of X-ray diffraction that the photoinduced nanoparticles have a crystalline phase, and also suggested from measurement of optical frequency doubling that the periodic nanoparticle structure exhibits second harmonic generation (SHG) with an unique polarization dependence of SHG based on nano-structures of dielectric polarization. In addition, such a simple method of phase mask usage was applied to formation of 2D array, and the 2D structures of nano-particles/holes were. successfully obtained by laser irradiations.

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DOI： 10.1063/1.1544059

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Second-order optical nonlinearities, d(33), of LaBGeO5, LiBGeO4 and Ba2TiGe2O8 crystals in transparent crystallized glasses were estimated by means of the Maker fringe technique. Transparent surface crystallized glasses were fabricated by crystallization of a glass with the exact or close stoichiometric composition of each crystal. The d(33) values of similar to0.13 pm/V for LaBGeO5, similar to0.7 pm/V for LiBGeO4 and similar to7 pm/V for Ba2TiGe2O8 crystals were obtained. The crystallized glass consisting of Ba2TiGe2O8 crystals with pyramidal TiO5 units has the largest d(33) value of the crystallized glasses reported so far, and its value is comparable to the d(22) value of LiNbO3 single crystal. It is proposed that LiBGeO4 and Ba2TiGe2O8 crystals can be considered as new candidates for optical nonlinear crystals.

DOI： 10.1143/JJAP.41.L1455

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DOI： 10.1063/1.1493667

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

Glasses with compositions corresponding to stillwellite-type (La,Ln)BGeO5 (Ln: Nd, Gd, Eu and Tin) crystalline phases hake been prepared, and the effect of lanthanide substitution,., on ferroelectric properties and second harmonic (SH) intensities of stillwellite-type crystalline phases formed by crystallization of glasses has been examined, The substitution of Ln(3+) for La3+ ions in the LaBGeO5 phase has been confirmed from the results of X-ray diffraction (XRD) analysis and fluorescence spectra of Eu3+ ions. The substitution of Ln(3+) for La3+, ions causes a decrease not only in the lattice constants but also in the a/c axis ratio. The amount of substitutions depends on the Ln(3+) I ionic radius. The Curie temperature of crystallized glasses increases almost linearly with decreasing mean ionic radius of lanthanides estimated from the composition of base glasses. A similar trend is observed in the SH intensity for crystallized glasses (powdered form). indicating the presence of a close relationship between Curie temperature and SH intensity. It is proposed from Raman spectra that the enhancement of SH intensities is caused by the change in the arrangements of BO4 and GeO4 tetrahedra in the (La,Ln)BGeO5 crystals due to the substitution of Ln(3+) ions having stronger Ln(3+)-O bonds. A clear second harmonic generation is observed in transparent surface crystallized glasses of the Nd2O3- or Gd2O3-substituted system.

DOI： 10.1143/JJAP.41.3771

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DOI： 10.1016/S0925-3467(02)00027-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The electronic polarizability and optical basicity of La2O3 and related glasses have been determined from ultraviolet absorption spectra and calculations based on the Lorentz-Lorenz equation. The optical basicity for La2O3 oxide is found to be 1.07, being much larger compared with typical glass-forming oxides such as B2O3 (0.42) and SiO2 (0.48) but being similar to heavy element oxides such as TeO2 (0.93). The Yamashita and Kurosawa's interaction parameter of La2O3 is 0.03 A(-3), indicating that La2O3 is classified as a normal ionic (basic) oxide, i.e., an ionic bonding character in the La3+-O bond is proposed. Close correlations are confirmed among optical basicity, interaction parameter, and oxygen 1s binding energy in x-ray photoelectron (XPS) spectra for La2O3-P2O5 and other La2O3-containing glasses. It is found from XPS and Raman spectra that La3+ ions in La2O3-P2O5 glasses act as network modifiers, supporting an ionic bonding character in the La3+-O bond. The parameters related to electronic polarizability in La2O3 determined in the present study would be useful for the design of rare-earth containing optical functional glasses. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1436292

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

The average electronic polarisability of the oxide ion (alpha(O2-)), optical basicity (Lambda),Yamashita Kurosawa's interaction parameter (A) and oxygen 1s (O1s) binding energy in x-ray photoelectron spectroscopy (XPS) of xBi(2)O(3) (100-x) B2O3 glasses (x=0similar to65) have been examined to check correlations among them and to clarify the electronic structure of the glasses and bonding character of Bi O. Both alpha(O2-) and Lambda increase gradually with increasing Bi2O3 content. and large alpha(O2) values over 2 A(3) and large Lambda values over 0.9 are obtained in the glasses with high Bi-O contents. The interaction parameter ranges from about 0.05 to 0.25 and decreases with increasing Bi2O3 content. The Ols peak in XPS spectra consists of two components: the Ols peak with higher binding energies. O1s(1), is assigned to B O-B bonds and that with lower binding energies O1s(2), correspond to Bi-O-B and Bi-O-Bi bonds. The O1s(1) binding energy decreases gradually with increasing, Bi2O3 content but the O1s(2) binding energy is almost constant suggesting that the ionic/covalent character of Bi-O bonds does not change significantly with composition. Close correlations are observed among alpha(O2-). A A and mean O1s binding energy. Particularly, it has been found that O1S binding energy is a good measure of the optical basicity of Bi2O3-B2O3 glasses and the interaction parameter gives good information about the electronic polarisability of oxide glasses as well as optical basicity. It is found that Bi-O bounds in Bi2O3-B2O3 glasses are more ionic compared with Sb O bonds in Sb2O3 B2O3 glasses.

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Language：English   Publisher：The Ceramic Society of Japan  

Crystallization behaviors of the glass with a composition of 25Li_2O・25B_2O_3・50GeO_2 corresponding to lithium borogermanate LiBGeO_4 have been examined. It has been confirmed that the LiBGeO_4 crystalline phase is formed at the surface of heat-treated glasses. The second harmonic(SH)generation is found from transparent surface crystallized glasses, demonstrating for the first time that the LiBGeO_4 phase shows optical nonlinearity. The SH intensity of LiBGeO_4 crystallites(powdered state)prepared through crystallization is about ten times as large as that of pulverized α-quartz. The SH intensity of transparent crystallized glasses(bulk state)with crystalline layers of 3-4.5 μm thickness increases with increasing heat treatment temperature(540-560℃)and time(1-6 h), and the maximum SH intensity among the samples studied is in the order of 1/10 in comparison with that of α-quartz single crystal. The transparent crystallized glass obtained by heat treatment at 550℃ for 3 h exhibits a clear and fine Maker fringe pattern, indicating a highly orientation of LiBGeO_4 crystals at the surface.

DOI： 10.2109/jcersj.110.22

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：VERLAG DEUTSCHEN GLASTECHNISCHEN  

A continuous wave (CW) Nd: YAG laser with a wavelength of 1064 nm was irradiated to Sm2O3-Bi2O3-B2O3 glasses and crystalline dots (diameter: similar to5mum) and lines (width: similar to3mum) consisting of the Bi0.7Sm0.3BO3 crystalline phase were formed. A second harmonic generation (SHG) was observed from each crystalline dot or line. It is suggested from polarized optical microscope observations and Maker fringe SHG measurements that each crystalline line is a single crystal line. It was confirmed that a nonlinear optical crystalline line works as an optical waveguide. Nonlinear optical beta-BaB2O4 crystalline dots were also fabricated in 11.1Sm(2)O(3)-44.4BaO-44.4B(2)O(3) glass by YAG laser irradiations. CW YAG laser irradiation to glass with Sm3+ is a nice technique for spatially controlled crystalline dot and line patterning.

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

New transparent surface crystallized glasses in the system of Sm2O3-Bi2O3-B2O3 have been successfully fabricated. The second harmonic generation (SHG) from the crystalline phase at the surface layers has been confirmed from Maker fringe measurements. The chemical composition of optical nonlinear crystals in the crystallized glass of 12.5Sm2O3 · 30Bi2O3 · 57.5B2O3 is determined to be Bi0.7Sm0.3BO3. The irradiation of a continuous-wave YAG laser with a wavelength of 1064 nm induces sharp refractive-index changes or crystalline dot formation, depending on Sm2O3 content in the glasses and laser irradiation condition. In 10Sm2O3 · 30Bi2O3 · 60B2O3 glass, refractive-index changes (not crystallites) are induced by laser irradiations (power: 1W, time: 1-250 s), and spherical spots with 2-45 μm are formed. In 12.5Sm2O3 · 30Bi2O3 · 57.5B2O3 and 16.5Sm2O3 · 26Bi2O3 · 57.5B2O3 glasses, crystalline dots with diameters of 5-65 μm are formed by laser irradiations (power: 0.5-0.7 W, times: 1-250 s). The lines consisting of refractive-index changes and crystallites are fabricated by scanning laser spots with the speeds of 5-25 μm · s-1. It is found that the crystalline phase formed by laser irradiation is the same as that precipitated by usual heat treatment in an electric furnace and thus the crystalline dots and lines generate optical second harmonic waves.

DOI： 10.2109/jcersj.110.398

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Optically transparent rare earth (Ln)-doped glass-ceramics based on the system K2O-Nb2O5-TeO2 have been prepared, and the effect of Ln additions on crystallization behaviors and optical properties has been examined. The lattice constant of the TeO2-based metastable optical nonlinear nanocrystalline phase (average particle size: &lt; 60nm) with basically a cubic structure in the glass-ceramics decreases due to Ln additions, and the incorporation of Ln(3+) with small ionic radii such as Er3+ or Tm3+ stabilizes the metastable crystalline phase, giving the significant effect on the crystallization and phase transformation behaviors in TeO2-based glasses. From the phonon sideband spectra associated with the (5)Do --&gt; F-7(0) transition of Eu3+, it is found that both phonon energy and electron phonon coupling strength for transparent glass-ceramics are smaller than those in the precursor glass. The upconversion fluorescence intensity around 550 nm due to the S-4(3/2) --&gt; I-4(15/2) transition of Er3+ is strong (about 20 times) compared with the precursor glass. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(01)00077-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The structural relaxation kinetics in the glass transition for xSb(2)O(3). (100-x)B2O3 glasses with covalent bonding character has been examined from viscosity and heat capacity measurements. These binary glasses have low glass transition temperatures, T-g=250-290 degreesC, but show a high thermal resistance against crystallization. The degree of fragility m estimated from the activation energy for viscous flow (E-eta=290-531 kJ mol(-1)) is m=29-51. The activation energy for enthalpy relaxation, DeltaH=297-602 kJ mol(-1), is evaluated from the cooling rate dependence of the limiting fictive temperature. The DeltaH values are very close to the E-eta values, meaning that the decoupling between enthalpy relaxation and viscous flow is small. The values of Kovacs-Aklonis-Huchinson-Ramos (KAHR) parameter theta estimated from DeltaH/RTg2 are 0.13-0.25, where R is the gas constant. The glasses with 30-60 mol % Sb2O3 have very similar E-eta, m, DeltaH, and theta values. It has been demonstrated that the structural relaxation kinetics of the binary antimony borate glasses is affected by the boron coordination numbers (i.e., BO3 and BO4) and the covalent bonding character of Sb-O bonds, and consequently these glasses are regarded as a highly strong glass-forming system in the fragile/strong classification concept. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1404990

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Language：English   Publisher：ELSEVIER SCIENCE BV  

CW YAG laser with a wavelength of 1064 mn and with a power of 1 W has been used to irradiate samarium. tellurite glasses with the compositions of 10RO (.) 10SM(2)O(3) (.) 80TeO(2) (R= Mg, Ba) at room temperature for 30-60 s. It is found from polarized optical microscopy and from X-ray diffraction (XRD) analyses that crystalline dot patterns with sharp refractive index changes are formed by laser irradiation. The diameters of the spherical dots in the glasses with BaO and MgO are about 50 and 150 tm, respectively. It has been proposed that the crystallization of a nanocrystalline Sm2Te6O15 phase is induced through the absorption of irradiated YAG laser by the Sm3+ ions. This is the first finding of crystalline dot patterning induced by infrared CW YAG laser irradiation in glass. (C) 2001 Published by Elsevier Science B.V.

DOI： 10.1016/S0022-3093(01)00736-0

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DOI： 10.1063/1.1360699

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

Crystallization behavior of BaO-Ln(2)O(3)-TeO2 glasses (Ln=La, Pr, Sm, Eu, Pr) was examined to prepare transparent crystallized glasses consisting of lanthanide tellurite crystals (Te4+ crystalline compounds) with low phonon energies, Transparent crystallized glasses with fluorite-type Ln(2)Te(6)O(15) or Ln(2)Te(5)O(13) nanocrystals (similar to 50 nm sizes) were successfully prepared for the first time. The crystallization mechanism depends strongly on the lanthanide species: surface crystallization (similar to 15 mum) is dominant in La3+ and Pr3+ containing glasses, but homogeneous nucleation occurs easily in Sm3+, EU3+ and Er3+ containing glasses, giving transparent bulk crystallized glasses. These transparent nano-crystallized glasses are applicable to fabrication of optical amplified waveguides or Bragg grating fibers.

DOI： 10.2109/jcersj.109.1269_466

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KLUWER ACADEMIC PUBL  

The hardness and elastic properties of 20PbO . xBi(2)O(3) . (80 - x)B2O3 glasses with x = 20-60 were evaluated through usual Vickers indentation and nanoindentation tests. The glass transition temperature (T-g = 295-421 degreesC), Vickers hardness (H-v = 2.9-4.5 GPa), true hardness (H = 1.5-3.8 GPa) and Young's modulus (E = 24.4-72.6 GPa) decreased monotonously with increasing Bi2O3 content. This compositional trend demonstrates that the strength of Bi-O chemical bonds in these glasses is considerably weak compared with B-O bonds and plastic deformations under indentation loading occur easily. The elastic recovery after unloading was about 45% for the glasses with x = 20-50, and the Poisson's ratio was 0.27 for the glass with x = 20. The fracture toughness was evaluated to be 0.37-0.88 MPam(1/2) from the values of H-v and E, and it was proposed that not only weak Bi-O bonds but also boron coordination polyhedra (BO3 or BO4) and their arrangements affect on crack formation. From the temperature dependence of Vickers hardness up to the glass transition region, it was suggested that the glasses with high Bi2O3 contents belong to the category to fragile glass-forming liquids. (C) 2001 Kluwer Academic Publishers.

DOI： 10.1023/A:1017973830342

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Science Publishers B.V.  

The average electronic polarizability of the oxide ion (αO(2-)) and optical basicity (Λ) of Sb2O3-B2O3 glasses have been estimated from the values of refractive index and optical band gap, and the O1s and Sb3d binding energies have been measured from X-ray photoelectron spectroscopy (XPS) spectra in order to clarify the electronic structure of oxide glasses. Both αO(2-) and Λ increase with increasing Sb2O3 content and conversely both O1s and Sb3d binding energies decrease. Close correlations are observed among them, and particularly it has been confirmed that the O1s binding energy is a good measure of the optical basicity of these glasses. The O1s signal in XPS spectra consists of two components: the O1s peak with higher binding energies is assigned to B-O-B bonds and that with lower binding energies corresponds to Sb-O-B and Sb-O-Sb bonds. It has been also suggested that a substantial rearrangement in the bridging oxygen bonding takes place at about 40 mol% Sb2O3: with a decrease in the number of B-O-B bonds and an increase in the number of Sb-O-B and Sb-O-Sb bonds. The covalency of Sb-O bonds increases with increasing Sb2O3 content, and its origin has been discussed in view of the good correlation between O1s and Sb3d binding energies, suggesting the formation of Sb-O bonds rich in p-character due to the increased probability of back donation of electron density from O2- to Sb3+ ions.

DOI： 10.1016/S0022-3093(00)00156-3

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Transparent, surface crystallised glasses containing a ferroelectric LaBGeO5 crystalline phase were successfully prepared through a two-step heat treatment in air (e.g. 670°C+750°C) for 25La2O3·25B2O3·50Ge O2 glass. The temperature of maximum nucleation rate was determined to be 670°C, from differential thermal analysis, which is consistent with the glass transition temperature. The LaBGeO5 crystalline phase was confirmed to be formed within the surface region to a depth of about 60 μm. The bulk crystallised glasses, obtained by heat treatments around the crystallisation temperature, were opaque. The second harmonic intensity from the transparent crystallised glasses was of the order of 11100 of that for α-quartz SiO2. Transparent surface crystallised glasses with La1-xGdxBGeO5 crystalline phases were also fabricated through a two-step heat treatment.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Ceramic Soc  

The kinetics of enthalpy relaxation (recovery) at the glass transition in xK2O·(20 - x)MgO·80TeO2 glasses has been examined from heat capacity measurements using differential scanning calorimetry to clarify the features of the structural relaxation in ternary TeO2-based glasses. Ternary glasses such as 10K2O·10MgO·80TeO2 show high thermal resistance against crystallization compared with binary glasses. The degree of fragility m estimated from the activation energy for viscous flow Eη and the glass transition temperature Tg is m = 55-62, indicating a fragile character in TeO2-based glasses. Large heat capacity changes of 43.1-48.2 J·mol-1·K-1 are also observed at the glass transition. The activation energy for enthalpy relaxation ΔH is evaluated from the cooling rate dependence of the limiting fictive temperature, and values of ΔH = 897-1268 kJ·mol-1 are obtained. Negative deviation from additivity in ΔH is also observed. Values of the Kovacs-Aklonis-Huchinson-Ramos (KAHR) parameter θ estimated from ΔH and Tg are 0.33-0.42 K-1. It has been proposed that ternary glasses have more homogeneous and constrained glass structure compared with binary glasses.

DOI： 10.1111/j.1151-2916.2000.tb01353.x

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Transparent surface crystallized glasses consisting of ferroelectric stillwellite-type LaBGeO5 crystalline phase and showing second harmonic generation were successfully prepared. The crystallized glasses were fabricated through two-step heat-treatment in air (e.g. 670 degrees C, 3 h + 750 degrees C, 5 h) for 25La(2)O(3). 25B(2)O(3). 50GeO(2) glass. The temperature of maximum nucleation rate was determined to be 670 degrees C from differential thermal analyses, which is consistent with the glass transition temperature. The LaBGeO5 crystalline phase was confirmed to be formed at the surface region of about 60 mu m and the grains were more oriented in the interior. The second harmonic intensity from the surface was in the order of 1/100 in comparison with that of quartz alpha-SiO2. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(99)00573-6

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The temperature dependence of Vickers hardness(H)of TeO_2-based glasses such as 15Na_2O・15ZnO・70TeO_2 as host glasses for rare-earth doped optical amplifier was measured from room temperature to the glass transition region. The following features were found ; (1)crack formation under the indenter easily occurs, the Vickers hardness at room temperature being around 3 GPa ; (2)the temperature coefficient of the hardness, dH/dT, is around -4.5×10^<-3>GPa・K^<-1> ; (3)the relative change of hardness with temperature is closely related to thermal expansion coefficient, and hardness sharply decreases in the glass transition region. It was demonstrated that TeO_2-based glasses are fragile even from the point of view of mechanical properties. The reason for poor mechanical performance in TeO_2-based glasses is their weak bond strength and open atomic packing structures. The hardness(H=4.8GPa)of a transparent glass-ceramic(with nanocrystalline particles)of 15K_2O・15Nb_2O_5・70TeO_2 showing second harmonic generation is much larger than that of the precursor glass(H=3.3 GPa), meaning that the improvement in the fragile character of TeO_2-based glasses is due to crystallization. A soda-lime silicate glass of 14Na_2O・13CaO・73SiO_2 has a value dH/dT=-6.5×10^<-3>GPa・K^<-1> and in contrast to TeO_2-based glasses, its hardness decrease in the glass transition region is gradual, and a value H&ap;2 GPa is obtained even at the glass transition temperature.

DOI： 10.2109/jcersj.107.1140

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Other Link： https://jlc.jst.go.jp/DN/JALC/00058182123?from=CiNii

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

The thermal stability and heat capacity changes in the glass transition region of K2O-WO3-TeO2 glasses (glass formation range 20-90 mol% TeO2) have been studied to examine the structural relaxation behavior. The glasses with 60-70 mol% TeO2 and with both K2O and WO3 are thermally stable against crystallization. It is proposed from Raman spectral analyses that TeO4 trigonal bipyramids change to TeO3 trigonal pyramids with the addition of K2O and that Te-O-W bonds are formed in the substitution of WO3 for TeO2. Heat capacity changes of Delta C-p = 48-58 J mol(-1) K-1 (Delta C-p = C-pl - C-pg, C-pg and C-pl are the heat capacities of the glasses and supercooled liquids, respectively), and ratios C-pl/C-pg = 1.6-1.8 are obtained for xK(2)O . xWO(3). (100 - 2x)TeO2 glasses. The Delta C-p and C-pl/C-pg increase with decreasing TeO2 content, indicating an increase in thermodynamic fragility with decreasing TeO2 content. But, the kinetic fragility estimated from the activation energy for viscous flow is almost constant irrespective of TeO2 content. These behaviors have been analyzed using the configurational entropy model proposed by Adam and Gibbs. The results indicate that in K2O-WO3-TeO2 glasses, Te-O-Te bonds are weak and bond breakings occur easily in the glass transition region, leading to large configurational entropy changes and thus large Delta C-p. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(98)00800-X

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

The heat capacity changes and enthalpy relaxation at the glass transition in mixed-alkali tellurite glass-forming liquids of (20 - x)Li2O-xNa(2)O-80TeO(2) with different fragilities have been measured. An increase in heat capacity, Delta C-p = 45 J mol(-1) K-1, is observed and the value is almost the same irrespective of the Na2O/(Na2O + Li2O) ratio, i.e. no mixed-alkali effect (MAE) on thermodynamic fragility. The ratio of the heat capacities of the glassy state (C-pg) and supercooled liquid state (C-pl), C-pe/C-pg, is 1.6, indicating that the above system should be included in the category of fragile liquids. The MAE is observed on the activation energy for the relaxation process at the glass transition, Delta H, i.e. the presence of MAE on the kinetic fragility. Although the structural units of TeO4 and TeO3 are connected weakly with each other and thus the intermediate structure varies with increasing temperature, the rearrangement kinetics of TeO4 and TeO3 during heating is affected by the alkali mixing. (C) 1997 Elsevier Science B.V.

DOI： 10.1016/S0022-3093(97)00361-X

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

Molecular dynamics (MD) simulations for silica glass and melt were carried out to evaluate the inhomogeneity of several structural units. This paper deals with the difference between the time and site variations of bond distances and bond angles, instead of treating MD model glass as a statistically averaged structure. The structural variation of local units, such as Si-O bonds and bond angles, showed a characteristic dependence on the temperature; in particular the Si-O-Si bond angles were distributed from site to site as widely as the time fluctuation at about 3000 K. According to the comparison with the other structural parameters or the thermodynamic properties, they are proved to be a most suitable variable for recognizing the glass transition phenomenon. Using the molecular orbital calculations, the possibility of estimating the inhomogeneity of electronic states is discussed.

DOI： 10.1016/0022-3093(94)00563-X

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Event date： 2007.12.8

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Venue：岡山理科大学  

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