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.     

Electrical properties of phosphate glasses

The electrical properties of glasses in the Na₂OP₂O₅, Ag₂OP₂O₅ and (1?x)Na₂OxAg₂OP₂O₅ systems have been measured over a range of temperature and composition.The properties of the Na₂OP₂O₅ and Ag₂OP₂O₅ glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na₂O?xAg₂O?P₂O₅ system was found around the mole ratio of 0.16:0.84 Ag₂O:Na₂O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the T_g-against-composition plots. A linear relationship was noted for the tan δ-versus-log₁₀ (resistivity) plot, as has been seen in other glass-forming systems.     

Bond character and properties of the mixed alkali system Na2OK2OAl2O3SiO2

The mixed alkali glass system Na₂OK₂OAl₂O₃SiO₂ was investigated. Density, transformation temperature, refractive index, and chemical durability were studied. Optical absorption and ESR spectra of the CuO-doped glasses were determined.Calculations of the polarizability of O^2?, bonding parameters of the Cu²⁺ complex, and the packing density are presented. It was found that for the mixed alkali glasses, the oxygen- alkali bond has a more ionic character than expected from additivity. This fact enables the non-linear changes of the refractive index, of the shift of the Cu²⁺ absorption band, and of the covalency to be interpreted as the Na mole fraction is varied. It is also possible to explain qualitatively the density, T_g and chemical durability non-linear variations with change of the Na content by the ionicity deviations of the bond character and the postulated pairs of Na⁺ and K⁺ ions in the mixed alkali glasses.     

Determination of ionic distributions of three sorts of oxygens in a few binary silicate glasses from molar refractivity

Ionic distributions of three sorts of oxygens in glasses in the systems Na₂OSiO₂K₂OSiO₂ and PbOSiO₂ were determined from molar refractivity. The distribution of these oxygen ions in PbOSiO₂ glasses was compared with that determined by the XPS method and with the theoretical calculation based on the athermal mixture model. The present result showed good agreement with that by the XPS method when the PbO content was 70 mol % or over, and showed a discrepancy when the PbO content was less than 70 mol %. It was indicated that a theoretical treatment based on a higher approximation that the athermal mixture model is required in order to enable the comparison with experiments for silica contents higher than 50 mol %.     

Editorial

NMR techniques are employed to determine the relative fractions of boron atoms in Na₂OB₂O₃SiO₂ glasses of high soda content. The data show that if enough Na₂O is added, four-coordinated borons are destroyed and borons with one or two non-bridging oxygens are created, but that both the beginning point and the rate of these processes depend strongly on the amount of silica present. These findings are shown to be quantitatively inconsistent with structural models previously suggested in the literature. Utilizing the concept of proportionate atomic sharing of the additional Na₂O, a new structural model is proposed for K K = mol% SiO₂/mol% B₂O₃) which is consistent with all the data including previously reported data for glasses in the region of relatively low soda content. Using R = mol% Na₂O/mol% B₂O₃, the new model states that for , all the additional Na₂O is employed in forming non-bridging oxygens on the silica tetrahedra; then for R_D1 R R_D3 = 2 + K, the fraction $\text{(K +}\text{1}\text{4}\text{K)/(2 + K)}$ of the additional Na₂O destroys reedmernerite groups and forms pyroborate units plus silica tetrahedra with two non-bridging oxygens per Si atom, while the fraction $\text{(2 ?}\text{1}\text{4}\text{K)/(2 + K)}$ of the additional Na₂O destroys diborate groups and forms additional pyroborate units.     

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.     

A discussion about the structural model of “nuclear magnetic resonance studies of glasses in the system Na2OB2O3SiO2”

The structural model for the system Na₂OB₂O₃SiO₂ suggested by Yun, Feller and Bray is discussed. A different structural model is suggested in this paper the results of which are in better agreement with experiment.     

Glass formation in the systems (K or Cs)2O(Nb or Ta)2O5Al2O3

The glass-forming ability of melts in the systems K₂O(Nb and/or Ta)₂O₅Al₂O₃ as well as those in which K₂O was replaced with Li₂O, Na₂O, Cs₂O, BaO or PbO was investigated. Some melts in the systems (K or Cs)₂O(Nb and/or Ta)₂O₅Al₂O₃ could be made into glasses by cooling, yielding practically useful amounts. The structures of these glasses were discussed on the basis of their infrared spectroscopic and X-ray emission spectroscopic analyses.     

X-ray diffraction studies of glasses in the systems Na2OMeOSiO2 (MeMg,Zn, Ca,Ba)

X-ray diffraction studies of glasses in the following ternary systems have been made: Na₂OMgOSiO₂, Na₂OZnOSiO₂, Na₂OCaOSiO₂ and Na₂OBaOSiO₂. The following heavy atom substitutions have been used: Ag for Na and Ge for Si. The changes in the electron radial distribution curves resulting from AgNa replacement can be explained as amplifications of relatively well-defined NaSi distances, which are nearly the same in all the glasses investigated. The GeSi substitution causes changes which can be explained on the basis of isostructural GeSi substitutions.     

Glass formation and structure of Na2SSiO2 and Na2SB2O3 glasses

Glass-forming regions of the systems Na₂SSiO₂ and Na₂SB₂O₃ have been investigated in order to clarify whether Na₂S could be substituted for Na₂O in sodium silicate or borate glasses, and the results were interpreted in terms of the structures of silicate and borate glasses. No difference was found in the glass-forming range of SiO₂ content between the Na₂SSiO₂ and Na₂OSiO₂ systems, and the red color of Na₂SSiO₂ glasses suggests that the formation of polysulfides in the glass structure is probably due to the entrance of sulfur ions in the non-bridging sites of the glass network. On the other hand, not all of the sulfur added to the glass batches could be retained in the Na₂SB₂O₃ glasses and the amount remaining in the glass products changed depending upon the amount of sodium ions in the glasses. Only a trace of sulfur was observed in the glasses containing less than 13 mol% of Na₂S in the batches, but the sulfur content in the glasses increased steeply with sodium content up to 35 mol%, reached the maximum and then decreased slowly with sodium content. The insolubility of sulfur in the glasses with low sodium content was interpreted based on the compositional dependence of basicity of alkali-borate glasses, and the change in solubility of sulfur with sodium concentration was explained based on the well-known boron anomaly caused by the change in the coordination state of boron and on the formation of non-bridging oxygens or sulfurs in the glass structure.     

Structure–property correlations in lead borate and borosilicate glasses doped with aluminum oxide

Glass samples from four systems: xPbO–(100?x)B₂O₃ (x = 30, 40, 50 and 60 mol%), 50PbO–yAl₂O₃–(50?y)B₂O₃ (y = 2, 4, 6, 8 mol%), 50PbO–ySiO₂–(50?y)B₂O₃ (y = 5, 10, 20, 30 mol%) and 50PbO–5SiO₂–yAl₂O₃–(45?y)B₂O₃ (y = 2, 4, 6, 8 mol%) were prepared by a melt-quench technique. Characterization of these systems was carried out using density measurements, UV–visible spectroscopy, differential scanning calorimetry (DSC), and ¹¹B and ²⁷Al magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR). Our studies reveal an increase in glass density with increasing lead(II) oxide concentration in pure lead borates and also with addition of silica into 50PbO–50B₂O₃ glass. ¹¹B MAS NMR measurements determine that the fraction of tetrahedral borons (N₄) reaches a maximum for the glass containing 50 mol% of PbO in the PbO–B₂O₃ glass series and that N₄ is sharply reduced upon adding small amounts of Al₂O₃ into lead borate and lead borosilicate systems. ²⁷Al MAS NMR experiments performed on glasses doped with aluminum oxide show that the Al³⁺ are tetra-, penta- and hexa-coordinated with oxygen, even without any excess concentration of Al³⁺ over charge-balancing Pb²⁺ cations. ^[5]Al and ^[6]Al concentrations are found to have unusually high values of up to 30%. The results of UV–visible absorption spectroscopy, DSC and density measurements support the conclusions drawn from the NMR studies, providing a consistent picture of structure–property relations in these glass systems.     

NMR studies on rapidly solidified SiO2Al2O3 and SiO2Al2O3Na2O-glasses

²⁷Al and ²⁹Si MAS NMR studies were performed on roller-quenched SiO₂Al₂O₃-glasses with Al₂O₃ contents ranging from 10 to 60 mol% and on SiO₂Al₂O₃Na₂O glasses containing 10 mol% Al₂O₃ and 2.5 to 10 mol% Na₂O. Pure aluminium silicate glasses show NMR peaks at 0, 30 and 60 ppm. The frequency distribution of the different Al-sites is not affected by the glass composition. In glasses of the system SiO₂Al₂O₃Na₂O the 30 ppm peak decreases to zero as the Na₂O content increases. The 30 ppm peak is assigned to distorted triclustered AlO-tetrahedra, rather than to fivefold coordinated Al. Triclustering of tetrahedra may provide for charge neutrality in glasses with molar excess of Al₂O₃ over Na₂O. As charge balance is increasingly achieved by addition of alkali ions, the tendency of tetrahedral triclustering is reduced, reflected by the disappearance of the 30 ppm peak in glasses containing ≥ 7.5 mol% Na₂O.     

Chemical durability of Na2OCaOSiO2 glasses in acid solutions

The resistance of Na₂OCaOSiO₂ glasses to acid solutions has been studied. The compositions studied were Na₂O · 4SiO₂, Na₂O · x CaO · (4?x) SiO₂ and a common electrode glass containing 22.63Na₂O and 5.58 CaO, mol%. The reaction was made at 40°C for about 3 h in 1N solutions of HCl, HNO₃ and H₂SO₄. Powdered glass samples were used and the reaction was followed by analyzing the solution for soda, lime and silica.The extraction rates of each constituent were measured. The effect of acid concentration was also studied for each glass using 10^?3–10N solutions of the three acids for a fixed time. The quantity of calcium extracted increased slowly at first with increasing calcium content in the glass, but rapidly when the lime content exceeded ≈10 mol%. Above this concentration, both calcium and sodium appears to pass into solution in the same proportion in which they are present in the glass. The extraction rate was found to depend on the type and concentration of the acid used, being least in H₂SO₄ and much higher and almost equal in both HCl and HNO₃.An attempt was made to correlate the results of decomposition of the soda-lime-silica glasses to their membrane potentials in acidic solutions.     

ESR and optical absorption of cupric ion in borate glasses

ESR and optical absorption of Cu²⁺ were measured in xNa₂O(100?x)B₂O₃ (1 ≤ x ≤ 75), x ZnO(100?x)B₂O₃ (46 ≤ x ≤ 64) and x Pb(100?x)b₂O₃ (20 ≤ x ≤ 75) glasses, where x is expressed in mol.%. Spin hamiltonian parameters and ligand field absorption energy changed abruptly in the regions of 15 ≤ x ≤ 23 and 37 ≤ x ≤ 55 in the soda system, while both parameters were hardly dependent upon the glass composition in zinc and lead systems. The magnitude of micro-environmental fluctuation of Cu²⁺-complexes in the glasses was estimated qualitatively and correlated with the distribution of the strength of π-bonding between cupric ion and oxygen in the glass. Typical network modifiers and intermediates behaved differently, especially in the composition region of invert glass; the large deformation of the coordination sphere of Cu²⁺ in lead glasses due to the stronger PbO bond resulted in the large distribution of $\text{g}{}_{\mathrm{}}$. The situation was reverse in the case of soda glasses.     

Electronic structure and properties of oxide glasses (II) Basicity measured by copper(II) ion probe in Na2OP2O5, K2OB2O3 and K2SO4ZnSO4 glasses

The correlation between the basicity of oxygens measured by the Cu(II) ion probe and the non-bonding electron density on oxygens in alkali borate glasses was considered. The basicity was measured for K₂OB₂O₃, Na₂OP₂O₅ and K₂SO₄ZnSO₄ glasses and categorized into two types, δ and π, according to the symmetry property of the bonding between a Cu(II) ion and oxygen. The π basicity for borate and phosphate glasses showed an abrupt increase in the vicinity of 17 and 50 mol% alkali oxide, respectively. The values of π-type basicity varied with the composition of glass, being larger in the order: sulfate < phosphate ? borate, whereas δ basicity was constant irrespective of the glass composition. Such a change of the basicity with the composition of glass was interpreted in terms of behavior of non-bonding levels of the ligand oxygens in a glass network.     

The effect of composition on spinel crystals equilibrium in low-silica high-level waste glasses

The liquidus temperature (T_L) and the equilibrium mass fraction of spinel were measured in the regions of low-silica (less than 42 mass% SiO₂) high-level waste borosilicate glasses within the spinel primary phase field as functions of glass composition. The components that varied, one at a time, were Al₂O₃, B₂O₃, Cr₂O₃, Fe₂O₃, Li₂O, MnO, Na₂O, NiO, SiO₂, and ZrO₂. In the low-silica region, Cr₂O₃ increased the T_L substantially less, and Li₂O and Na₂O decreased the T_L significantly less than in the region with 42-56 mass% SiO₂. The temperature at which the equilibrium mass fraction of spinel was 1 mass% was 25-64 °C below the T_L.     

Ultrasound propagation in glasses in the metastable immiscibility region of the sodium borosilicate system

Measurements of ultrasound wave velocity and attenuation have been made between 1.3 K and 400 K in a series of both quenched and heat-treated Na₂OB₂O₃SiO₂ glasses. As in many other inorganic glasses, the ultrasound attenuation of both longitudinal and shear waves below room temperature is dominated by a broad and intense loss peak; the height and temperature of the peak maximum are frequency sensitive. The loss peak characteristics are consistent with a structural relaxation mechanism with a distribution of activation energies and this model is used to analyse the data. The features of the acoustic loss peak and also the absolute value and temperature coefficient of ultrasound velocity are strongly dependent on the total Na₂O network modifier content of the glasses. The ultrasound wave propagation is also affected by phase-separation inducing heat treatment: a steady rise in the height of the acoustic loss peak and an upward shift in the peak temperature takes place with increasing time of heat treatment at 550°C, a finding which suggests that structural rearrangements are still occurring in the individual glassy phases even after long periods of heat treatment. It is proposed that heat treatment causes migration of Na⁺ ions away from BOB bonds in the B₂O₃ rich phase.     

Studies on binary silicate glasses based on the SiKα and SiKß emission X-rays

The SiKα and Kβ X-ray emission spectra of binary silicate glasses of the Li₂O–SiO₂, Na₂O–SiO₂, K₂O–SiO₂, Cs₂O–SiO₂, B₂O₃–SiO₂, and GeO₂–SiO₂ systems were measured with an X-ray fluorescence spectrometer to examine the chemical effects on the spectra. The SiKα peak wavelengths for all the glasses agreed with that for SiO₂ glass, which corresponded to the concept that the coordination number of Si shouldbe four in all the glasses examined in this study. The SiKβ peak wavelength decreased with increasing alkali content in the alkali silicate glasses, indicating that the Si–O bond weakend in average as the alkali oxide was added to SiO₂ glass. On the other hand, no drastic shift in the SiKβ peak wavelength was observed in the B₂O₃–SiO₂ and GeO₂–SiO₂ systems, and this was interpreted as showing the constancy of Si–O bond strength in these glasses.     

Mössbauer spectra in the xNa2O·(1 − x − y)B2O3·yFe2O3 glass system

A Mössbauer spectroscopic study is made on xNa₂O·(1 ? x ? 7)B₂O₃·yFe₂O₃; 0.045 ? x ? 0.405 and y = 0.05, 0.10 and 0.15 samples quenched from the melt. The presence of two quadrupole doublets indicates that an amphoteric cation like Fe³⁺ occupies both the tetrahedral “network forming” and the octahedral “network modifying” sites in the glass structure. The observed variations of isomer shift and quadrupole splitting with the values of x are similar to the ones found earlier in lead borates but different from those observed earlier in soda borates and other alkali alumino borates. In samples with smaller values of x, an additional devitrified magnetic phase of Fe₂O₃ is seen. The distribution of Fe³⁺ ions in different sites and phases is also discussed.     

The effect of composition on the structure of sodium borophosphate glasses

Glasses in the system 40(P₂O₅)-x(B₂O₃)-(60 − x)(Na₂O) (10 ? x ? 30 mol%) have been prepared by the melt-quenching technique. Thermal properties were studied using differential thermal analysis and the relationship between composition and thermal stability was obtained. Structural characterization was achieved by a combination of experimental data (infrared and Raman spectroscopy, ¹¹B and ³¹P solid state NMR). In particular, variations in the phosphate network structure upon addition of B₂O₃ and Na₂O were investigated. Analysis of the data indicates that with increasing B₂O₃ content and decreasing Na₂O, the glass network shows increasing levels of cross-linking between phosphate and borate units. Evidence of direct B-O-P bonds was observed. In the compositional range investigated, borate groups contain boron almost exclusively in four-fold coordination.