Faculty Profiles - BENINO Yasuhiko

Papers - BENINO Yasuhiko

Division display 121 - 140 of about 141 ／ All the affair displays >>

YAG laser-induced nonlinear optical crystalline dot and line patterning in glasses Reviewed

T Komatsu, T Honma, H Tanaka, Y Benino, T Fujiwara

GLASS SCIENCE AND TECHNOLOGY 75 13 - 18 2002

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.

Optical nonlinear crystalline dot and line patterning in samarium bismuth borate glasses by YAG laser irradiation Reviewed

Tsuyoshi Honma, Yasuhiko Benino, Takumi Fujiwara, Ryuji Sato, Takayuki Komatsu

Journal of the Ceramic Society of Japan 110 ( 1281 ) 398 - 402 2002

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

Densification energy during nanoindentation of silica glass

Keiichi Suzuki, Yasuhiko Benino, Takumi Fujiwara, Takayuki Komatsu

Journal of the American Ceramic Society 85 ( 12 ) 3102 - 3104 2002

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

Load/unload displacement curves at room temperature (humidity 49%) for silica glass have been measured in the penetration range of 0.5-1.2 μm using a Vickers nanoindentation technique (load/unload speed 50 mN/s). Deformation energies have been estimated for the first time. The universal (dynamic) hardness, Hu, and elastic recovery, ER, at the penetration depth, ht, of 1.0 μm are Hu = 4.1 GPa and ER = 0.7. The following energies for total deformation, Ut, elastic deformation, Ue, and plastic deformation (i.e., densification during loading), Up, are obtained: Ut=190, Ue=135 and Up = 55 kJ/mol at ht = 0.5 μm and Ut = 139, Ue = 96 and Up = 43 kJ/mol at ht = 1.0 μm. All these deformation energies increase with decreasing penetration depth. It is found that plastic deformation energies of 38-55 kJ/mol for 0.5 &lt
ht &lt
1.2 μm are very close to the activation energy (46-54 kJ/mol) for the recovery of densification in silica glass, but are very small compared with the single bond strength (443 kJ/mol for Si-O bond) of SiO2.

DOI： 10.1111/j.1151-2916.2002.tb00590.x

Rare earth doping into optical nonlinear nanocrystalline phase in transparent TeO2-based glass-ceramics

K Hirano, Y Benino, T Komatsu

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 62 ( 11 ) 2075 - 2082 2001.11

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: < 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 --> 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) --> 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

Structural relaxation kinetics of antimony borate glasses with covalent bonding character Reviewed

T Honma, Y Benino, T Komatsu, R Sato, Dimitrov, V

JOURNAL OF CHEMICAL PHYSICS 115 ( 15 ) 7207 - 7214 2001.10

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

YAG laser-induced crystalline dot patterning in samarium tellurite glasses

R Sato, Y Benino, T Fujiwara, T Komatsu

JOURNAL OF NON-CRYSTALLINE SOLIDS 289 ( 1-3 ) 228 - 232 2001.8

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

Second harmonic generation in transparent surface crystallized glasses with stillwellite-type LaBGeO5 Reviewed

Y. Takahashi, Y. Benino, T. Fujiwara, T. Komatsu

Journal of Applied Physics 89 ( 10 ) 5282 - 5287 2001.5

Transparent surface and bulk crystallized glasses with lanthanide tellurite nanocrystals

Y Fujimoto, Y Benino, T Fujiwara, R Sato, T Komatsu

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 109 ( 5 ) 466 - 469 2001.5

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

Hardness and elastic properties of Bi2O3-based glasses

T Watanabe, K Muratsubaki, Y Benino, H Saitoh, T Komatsu

JOURNAL OF MATERIALS SCIENCE 36 ( 10 ) 2427 - 2433 2001

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

Unusual Elastic and Mechanical Behaviors of Copper Phosphate Glasses with Different Copper Valence States

Tadashi Miura, Toshio Watanabe, Yasuhiko Benino, Takayuki Komatsu, Ryuji Sato

Journal of the American Ceramic Society 84 ( 10 ) 2401 - 2408 2001

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

Elastic and mechanical properties such as Young's modulus E, Poisson's ratio v, Debye temperature θD, Vickers hardness Hv, fracture toughness Kc, and fracture surface energies γf of yCuOx ·(100-y)P2O5 glasses (y = 45, 50, 55) with different copper valence states, i.e., R(Cu+) = Cu+/(Cu+ + Cu2+), at room temperature (humidity 64%) have been examined. The following features have been found: (1) the glass transition temperature (218-434°C), Hv (2.7-4.4 GPa), E (50.6-78.2 GPa), and θD (358-434 K) decrease largely with increasing R(Cu+)
(2) the mean atomic volume, Kc (0.56-1.14 MPa·m1/2), and γf (1.9-11.2 J·m-2) tend to increase with increasing R(Cu+)
(3) 50CuOx·502PO5 glasses with R(Cu+) = 0.42 and 0.55 have a high resistance against crack formation in Vickers indentation tests and no crack is observed in the 45CuOx·55P2O5 glass with R(Cu+) = 0.57 under an applied load of about 98 N. The results demonstrate that elastic and mechanical properties of yCuOx·(100-y)P2O5 glasses depend strongly on the copper valence state and the CuOx/P2O5 ratio. The unusal mechanical and elastic properties of copper phosphate glasses are well explained qualitatively by considering unique oxygen coordination and bonding states of Cu+ ions, i.e., lower coordination number and more covalent bonding compared with Cu2+ ions.

DOI： 10.1111/j.1151-2916.2001.tb01021.x

Electronic polarizability, optical basicity and XPS spectra of Sb2O3-B2O3 glasses Reviewed

Tsuyoshi Honma, Ryuji Sato, Yasuhiko Benino, Takayuki Komatsu, Vesselin Dimitrov

Journal of Non-Crystalline Solids 272 ( 1 ) 1 - 13 2000

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

Transparent optical nonlinear crystallised glasses with ferroelectric LaBGeO5

Y. Takahashi, Y. Benino, V. V. Dimitrov, T. Komatsu

Physics and Chemistry of Glasses 41 ( 5 ) 225 - 228 2000

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

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.

Kinetics of enthalphy relaxation at the glass transition in ternary tellurite glasses

Kazuya Aida, Yasuhiko Benino, Vesselin Dimitrov, Takayuki Komatsu, Ryuji Sato

Journal of the American Ceramic Society 83 ( 5 ) 1192 - 1198 2000

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

Transparent surface crystallized glasses with optical non-linear LaBGeO5 crystals

Y Takahashi, Y Benino, Dimitrov, V, T Komatsu

JOURNAL OF NON-CRYSTALLINE SOLIDS 260 ( 1-2 ) 155 - 159 1999.12

Language：English Publisher：ELSEVIER SCIENCE BV

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

Temperature dependence of Vickers hardness of TeO₂-Based and soda-lime silicate glasses

Toshio WATANABE, Yasuhiko BENINO, Kozo ISHIZAKI, Takayuki KOMATSU

Journal of the Ceramic society of Japan(jointly worked) 107 ( 1252 ) 1140 - 1145 1999

Language：English Publisher：The Ceramic Society of Japan

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≈2 GPa is obtained even at the glass transition temperature.

DOI： 10.2109/jcersj.107.1140

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

Preparation and optical properties of transparent tellurite based glass ceramics doped by Er3+ and Eu3+

H. Oishi, Y. Benino, T. Komatsu

Physics and Chemistry of Glasses 40 ( 4 ) 212 - 218 1999

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

Optically transparent Er3+ and Eu3+ doped (less than 1.5 mol% Er2O3 and Eu2O3) glass ceramics based on the system K2O-MgO-Nb2O5-TeO2 have been successfully prepared for the first time. Addition of Er3+ and Eu3+ is effective for the formation of a crystalline phase showing second harmonic generation. Fluorescence spectra of Er3+ and Eu3+ in glass ceramics are almost similar to those in precursor glasses. The intensity of frequency upconversion fluorescence at around 550 nm due to the 4 S312→4I1512 transition of Er3+ in the glass ceramics is strong compared with that in their precursor glass. From the phonon sideband spectra associated with 5D2→7F0 transition of Eu3+ it is found that the phonon energy for transparent glass ceramics is smaller than that in the glasses, indicating that the multiphonon relaxation rate of Er3+ and Eu3+ present in TeO2 based glass ceramics is smaller than that in the corresponding TeO2 based glasses. Whether Er3+ and Eu3+ are incorporated into the crystalline phase or not is unclear the present study gives a new possibility for optical applications of transparent TeO2 based glass ceramics.

Thermal stability and heat capacity changes at the glass transition in K2O-WO3-TeO2 glasses

T Kosuge, Y Benino, Dimitrov, V, R Sato, T Komatsu

JOURNAL OF NON-CRYSTALLINE SOLIDS 242 ( 2-3 ) 154 - 164 1998.12

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

Heat capacity changes and structural relaxation at glass transition in mixed-alkali tellurite glasses

T Komatsu, T Noguchi, Y Benino

JOURNAL OF NON-CRYSTALLINE SOLIDS 222 206 - 211 1997.12

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

Temperature dependence of specific heat of sodium tellurite glasses Reviewed

K Tanaka, K Hirao, K Kashima, Y Benino, N Soga

PHYSICS AND CHEMISTRY OF GLASSES 38 ( 2 ) 87 - 91 1997.4

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

Specific heat of sodium tellurite glasses has been measured at 80-673 K to evaluate bonding characteristics and structural relaxation in the glass transition region from the values of specific heat at low and high temperatures, respectively The temperature variation of specific hear at 80 K room temperature has been analysed in terms of a three band model which describes the vibrational density of stare for glass in terms of three characteristic temperatures theta(1), theta(2) and theta(E); these parameters correspond to the interatomic vibration in the glass network intermolecular type interaction in glass network and vibration of network modifying cation, respectively. The values of 81 of sodium tellurite glasses are 820-840 K which are smaller than those of silicate borate, germanate and phosphate glasses This fact effects the weak bond strength of Te-O. The specific heat data at room temperature to 673 K have been used for the analysis of glass transition. The activation enthalpy relevant to the cooling rate dependence of glass transition temperature obtained on the basis of the Tool-Narayanaswamy model lies in 690-1100 kJ/mol range depending on glass composition.

EVALUATION OF STRUCTURAL INHOMOGENEITY BY MOLECULAR-DYNAMICS METHOD - STRUCTURAL VARIATION OF SILICA GLASS Reviewed

Y BENINO, K HIRAO, N SOGA

JOURNAL OF NON-CRYSTALLINE SOLIDS 183 ( 1-2 ) 22 - 30 1995.4

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

　 PREV - NEXT 　

1
2
3
4
5
6
7
8