Spectral absorption of tellurium in alkali borate glasses

The spectral absorption of tellurium-containing lithium, sodium and potassium borate glasses in the range of 300–700 nm was used to identify the states of tellurium formed in such glasses. Depending on the nature and concentration of the alkali oxide the glasses obtained were either colourless, rose which is attributed to the formation of the polytelluride ion or grey which is attributed to the formation of elemental tellurium particles. The tellurites and/or tellurates are expected to form in glasses of high content of either Na₂O or K₂O which were colourless. The sequence of formation of the different states of tellurium with increasing alkali content is in accordance with acidity-basicity concept.     

Composition dependence of the optical absorption spectra of cupric ion in sodium borosilicate glass melts

Optical absorption spectra of Cu²⁺ d–d transition peak in sodium borosilicate glasses and their melts were measured from room temperature to 1100 K. In the case of borate glass free from silicon, increase of the temperature above T_g shifts the peak position to the low energy side and decreases the peak height. Peak width is gradually increased with the increase in temperature. On the other hand, in the case of silicate glass free from boron, peak width is decreased with the increase in temperature from room temperature to liquidus temperature. In addition, peak height is slightly decreased with the temperature increase in this temperature range. Further increase of the temperature makes the peak width large. In borosilicate glasses, temperature dependence of the optical absorption spectra is different both from borate and from silicate, and the temperature dependences of the peak position and of the peak height are very small. Temperature dependence of the peak width depends on the boron/silicon ratio.     

Elastic properties of fast ion conducting lithium based borate glasses

Elastic properties of Li₂O–PbO–B₂O₃ glasses have been investigated using sound velocity measurements at 10 MHz. Four series of glasses have been investigated with different concentrations of Li₂O, PbO and B₂O₃. The variations of molar volume have been examined for the influences of Li₂O and PbO. The elastic moduli reveal trends in their compositional dependence. The bulk and shear modulus increases monotonically with increase in the concentration of tetrahedral boron which increases network dimensionality. The variation of bulk moduli has also been correlated to the variation in energy densities. The Poisson’s ratio found to be insensitive to the concentration of tetrahedral boron in the structure. The experimental Debye temperatures are in good agreement with the expected theoretical values. Experimental observations have been examined in view, the presence of borate network and the possibility of non-negligible participation of lead in network formation.     

Optical absorption of cobalt (II) in binary thallium borate glasses

The optical absorption spectra of cobalt (II) in Tl₂OB₂O₃ glasses have been studied and compared with those in binary alkali borate glasses. In thallium borate glasses cobalt (II) may be present in octahedral and/or in tetrahedral symmetry depending upon the composition of the glass. In low thallium borate glasses cobalt (II) is octahedral while the concentration of tetrahedral cobalt (II) increases with increasing Tl₂O content of the glass; the formation of tetrahedral cobalt (II) becomes noticeable when the concentration of Tl₂O reaches above the critical concentration of about 19 mol %. The ligand field parameters: 10Dq and B have been calculated from the absorption spectra of cobalt (II) in different glasses and it has been found that the Racah parameter, B, is more in Tl₂OB₂O₃ glasses than those in Na₂OB₂O₃ or K₂OB₂O₃ glasses of corresponding molar composition. This indicates that the donor capacity of the BO₄ group in thallium borate glasses is lower than that in alkali borate glasses; this is consistent with the NMR results in Tl₂OB₂O₃ glasses containing less than 20 mol % Tl₂O where three BO₄ groups have been found to form with each Tl₂O unit added.     

Internal friction in phosphoaluminate and borate glasses

Internal friction in sodium phosphoaluminate and borate glasses was investigated by torsion pendulum, beam vibration and pulse-echo methods. The Arrhenian relationship was verified in a frequency interval covering eight decades. A detailed analysis of the first peak was made to obtain the distribution of relaxation times and the distribution of activation entropy ΔS and activation enthalpy ΔH. The log-normal distributions were further compared to the Doremus theory and the observed discrepancy discussed.     

Mixed-alkali effect in alkali borate glasses

The spectral absorption of Cu²⁺ and Ni²⁺, the density, molar volume, refractive index, molar refraction, thermal expansion coefficient, transformation and dilatometric softening temperatures of mixed alkali borate glasses are reviewed. These results indicate that in borate glasses, mixed alkalis do not produce gross alterations of the glass network, and that the weak deviations observed may be related to the boric oxide anomaly.     

Scattering losses in binary borate glasses

The purpose of this paper is to examine the potential of three binary borate glasses; namely PbOB₂O₃, K₂OB₂O₃ and Li₂OB₂O₃ as candidates for fabrication of low optical loss and low cost fiber-glass wave-guides.The importance of ultrasonic measurements as the first step in a systematic search for a glass with low optical loss, is discussed. Results of ultrasonic measurements of PbOB₂O₃ system are then presented. Using these results and the published results for the K₂OB₂O₃ and Li₂OB₂O₃ systems, estimates of the magnitude of density fluctuations as a function of composition have been made for each system. Comparison with the previously published results on the K₂OSiO₂ system suggests that out of the three systems chosen, only 50 mole % Li₂O50 mole % B₂O₃ glass is a likely candidate for the production of low optical loss glass fibers.     

Dielectric relaxation in iron-containing borate glasses

The ac and dc conductivities, dielectric constant and dielectric loss of a series of calcium borate glasses containing Fe₂O₃ up to 10 mol% were measured as a function of temperature (300–700 K) and frequency (10²–10⁵ c/s). Glasses melted in platinum crucibles were found to show slightly higher dielectric constants and conductivities than glasses melted in zirconia crucibles under the same melting conditions. Relaxation effects with a distribution of relaxation times were observed for all the glasses of this system. The data show that the pre-exponential factor τ₀ is about 10^?11 s. Peaks in tan δ were found to shift to higher temperatures when the frequency of measurements was increased. Activation energy for dc conduction was found to be equal to that of ac conduction. No polarization effects were observed in these glasses, indicating that conduction is predominantly electronic.     

The effect of copper ions addition on structural and optical properties of zinc borate glasses

Glasses in the ternary system xCuO?(100 ? x)[55B₂O₃·45ZnO] (0 ≤ x ≤ 20 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The effect of copper ions addition in 55B₂O₃·45ZnO glass matrix together with the matrix effect on paramagentic behavior has been investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), electron paramagnetic resonance (EPR), ultraviolet–visible (UV–VIS) spectroscopy and density measurements. The increase of the number of non-bridging oxygen (NBO) atoms as a function of CuO content in these glasses leads to the decrease of glass polymerization which reduces the stability of the glasses and favors the association of copper ions in clusters. This leads to the major changes of structural and optical properties of the studied glasses as can be seen from the data obtained by FTIR and EPR spectroscopies.     

A study of optical absorption in some sodium titanium silicate glasses

A series of glass specimens was prepared from mixtures of SiO₂, TiO₂ and Na₂O, and their optical absorption coefficients measured as functions of photon energy in the range 2.1–3.3 eV. From the results, values of the optical energy gap are calculated and found to be dependent on the glass compositions. The results are analysed in terms of a mechanism of optical absorption arising from forbidden indirect transitions.     

MNDO studies of basicity in borate glasses

The cluster approximation was adopted for the borate glasses. The geometries and basicity of various isomers of H₈B₉O₁₈⁻, H₈B₁₁O₂₁⁻ and H₈B₁₂O₂₃²⁻ were studied by the MNDO semi-empirical molecular orbital method. The optimized geometries of pentaborate, triborate and diborate structure in the clusters showed good agreement with the experimentally determined ones. The changes of bond length and charge rearrangements accompanying the formation of a four-fold coordinated boron atom (⁴B) accorded with the prediction of Gutmann's bond length variation rule. The basicity in the borate glass was defined as the electron donability of oxygens in the glass network. MO interaction between the occupied orbitals of the clusters and the LUMO of the acidic site in (H₂B₉O₁₄)₂O and the proton affinity of the clusters were estimated. The basicities of the clusters which contained ⁴B and that of the clusters which contained non-bridging oxygen atoms (NBO) were compared. The appearance of NBO in high alkali borate glass was interpreted.     

Structure of lithium borate and strontium borate glasses with high modifier contents

The structure of lithium borate and strontium borate glasses with high Li₂O and SrO contents was examined using the experimental results of ESR and the optical absorption of Cu²⁺ ions, and the Mössbauer spectra of Fe³⁺ ions and Raman spectra of these glasses. The results indicate the existence of non-bridging oxygens belonging to orthoborate and pyroborate groups, structural groups of diborate and high pressure forms of metaborate above 30 mol% of the modifier contents in these glasses. Among these four structural groups, the diborate group rapidly decreased with an increase of the modifier contents, while the other three groups increased with an increase of the modifier contents.     

Hydration of phosphate and borate glasses in an autoclave

Kinetics of hydration of CaO---Al₂O₃---P₂O₅ and Na₂O---CaO---B₂O₃---Al₂O₃ glasses in an autoclave at high temperatures and high pressures has been investigated. The hydration of the phosphate glasses may occur as a result of hydrolysis of glass constituents to form orthophosphate crystals. Cabal glasses which do not contain any alkali oxides have shown a quite high resistance to water. Substitution of sodium for calcium deteriorates the chemical durability of Cabal glasses.     

Conductivity and optical absorption of semiconducting WO3 glasses

The dc conductivity and optical properties of WO₃---B₂O₃---ZnO glasses containing up to 80% WO₃ have been measured and are analyzed using small polaron hopping theory. The thermal hopping energy E_H is estimated from the temperature dependence of the conductivity, but an accurate determination of its value is not possible due to the continuous curvature of the conductivity plots. The optical absorption is dominated by W⁵⁺ ligand field absorption in the visible and by a band edge at 3.5 eV; the absorption by the small polarons is too weak to be observed directly. The optical hopping energy E_o is determined from the thermomodulation spectra. The values obtained for E_H and E_o can be combined to give a polaron binding energy and a disorder energy both approximately equal to 0.4 eV. A similar disorder energy is obtained from an analysis of the electro-modulation spectra in the band edge region.     

Sintering and crystallization of titanium-containing lead borate glasses

The sintering and crystallization of glass powders with chemical composition 47 PbO—38 B₂O₃—15 TiO₂ (mole %) was investigated under non-isothermal conditions by shrinkage measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD), dielectric measurement and positron annihilation (Doppler broadening). The correlation between changes of macroscopic properties and positron annihilation results recommends this method for the detection of structural changes in glasses.     

Alkali diffusion and electrical conductivity in sodium borate glasses

The diffusion coefficient of sodium, ²²Na, and silver, ¹¹⁰Ag, and electrical conductivity for sodium borate glasses (4–24 mol% Na₂O) has been measured from 100°C to slightly below the glass transition temperature, T_g. Unlike silicate glasses where the self-diffusion coefficient is much larger than the impurity diffusion coefficient, D_Na and D_Ag had close to the same magnitude in the sodium borate glasses. In some glasses, D_Ag was slightly larger than D_Na. Na₂O-Ag₂O-B₂O₃ glasses show a relatively small mixed alkali effect, despite the significant mass difference between Ag(≈108) and Na(≈23). It is concluded that the mixed alkali effect is more dependent upon the difference in ionic radii rather than differences in mass.     

Rheological properties of potassium barium borate glasses

Several series of potassium barium borate glasses have been investigated as to their rheological properties.It has been found, that all these glasses show deviations from ‘Newtonian’ behaviour below temperatures corresponding to viscosities of 10¹⁰ poises. The activation energies of viscous flow are linear in both the potassium and barium mole percentages.For the ternary systems the pre-exponential factors of the viscosities do not decrease considerably with increasing metal ion content, contratry to what has been found in binary systems.