Considerations on the structure and physical properties of B2O3-SiO2 and GeO2-SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B₂O₃-SiO₂ and GeO_2-SiO₂ glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B₂O₃, GeO₂ and SiO₂. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO₃, GeO₄ and SiO₄ units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si-O-B or Si-O-Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B₂O₃ or GeO₂ in the concerned glasses.     

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.     

Anomalous physical properties and Raman spectra of glassy B2O3BaTiO3Na2O materials

Anomalous physical properties (refractive index and density) of B₂O₃BaTiO₃Na₂O ternay glasses are determined and discussed on the basis of the structure present in the glasses and evidenced by vibrational Raman spectroscopy.These glasses behave in a manner analogous to the alkali B₂O₃X₂O binary glasses for molar ratio R = basic oxide/B₂O₃ up to 0.3, with oxygen binding by means of bridging bonds while boron coordination changes from the trigonal to tetrahedral type. The phenomenon is indicated by a progressive weakening of the 806 cm^?1 peak (attributable to a breathing vibration of the boroxol unit) and by a concomitant strengthening of the ～775 cm^?1 peak (attributable to a vibrational mode of boroxol units, or derived units, containing at least one 4-coordinate boron atom). For higher R values the Raman spectra bring to light the progressive demolition of the structural units responsible for the 775 cm^?1 Raman peak, which gives rise (the transformation is complete for R ～ 1) to two new main structural units, orthoborate [BTi₄O₁₀]^?1 (peak at 845 cm^?1) and metaborate BO₂^? (peak at 715 cm^?1).     

The role of Al3+ ions in alumino borate glasses as revealed by molar volume,refractive index and microhardness

An attempt has been made determine the types of Al³⁺ structural units in potassium alumino borate glass. Therefore a number of investigations have been carried out on the relation between the composition of the glasses and their properties. The density, refractive index, and hardness of a number of compositions in which Al₂O₃ replaces B₂O₃ at constant K₂O were measured. It appears that the replacement of B₂O₃is not entirely without some consequencies.The concentration of non-bridging oxygen ions increases with the introduction of Al₂O₃.Non bridging oxygen ions start aappearing at alkali concentration of about 0.2 mol K₂O.     

Structural analysis and devitrification of glasses based on the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives

Glasses, whose basic composition was based on the CaO-MgO-SiO₂ system and doped with B₂O₃, P₂O₅, Na₂O, and CaF₂, were prepared by melting at 1400 °C for 1 h. Raman and infrared (IR) spectroscopy revealed that the main structural units in the glass network were predominantly Q¹ and Q² silicate species. The presence of phosphate and borate units in the structure of the glasses was also evident in these spectra. X-ray analysis showed that the investigated glasses devitrified at 750 °C and higher temperatures. The crystalline phases of diopside and wollastonite dominated, but weak peaks, assigned to akermanite and fluorapatite, were also registered in the diffractograms. The presence of B₂O₃, Na₂O, and CaF₂ had a negligible influence on the assemblage of the crystallized phases, but it caused a reduction of crystallization temperature, comparing to similar glasses of the CaO-MgO-SiO₂ system.     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.     

Quenched glasses in the systems of Li2O with Al2O3, Ga2O3 and Bi2O3

By rapid quenching in a twin roller apparatus, glass was found to occur widely in the systems of Li₂O with Al₂O₃, Ga₂O₃, Bi₂O₃ and in mixed systems. Examination of the resulting flakes by X-ray powder diffraction, differential thermal analysis, and capacitance data revealed the occurrence of glass, glass transitions, crystallization exotherms and the nature of some of the crystallization paths.The log ionic conductivity of the glasses was found to follow a linear relationship with the Li concentration. Evidence was observed for three new metastable crystalline phases, one in the Li₂OAl₂O₃ system and two in the Li₂OBi₂O₃ system. The latter system also showed evidence for the occurrence of two glasses at almost all compositions.     

Density-structure correlations in Na2O-CaO-P2O5-SiO2 bioactive glasses

Relations for Na₂O-CaO-SiO₂ glasses have been developed to calculate the density of Na₂O-CaO-P₂O₅-SiO₂ bioactive glasses. The calculation makes use of NMR results of O’Donnell et al. indicating that P₂O₅ forms a separate phase, containing Na₃PO₄ and Ca₃(PO₄)₂, in the investigated glasses. The volume of the silicate units is the same as that found in Na₂O-CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂ glasses. Similarly, the volume of PO₄ units is equivalent to that in Na₃PO₄ and Ca₃(PO₄)₂. Calculated densities are consistent with the experimental data.     

The effect of RO (R = Mg,Ca, Ba and Zn) on physical properties of Na2O/Al2O3/B2O3/SiO2 glasses for the preparation of gradient index micro lenses

Glasses in the system Na₂O–Al₂O₃–B₂O₃–SiO₂ doped with MgO, CaO, BaO or ZnO (concentrations: 2.5%–5 mol%) were melted from the raw materials and studied with respect to their densities, hydrolytic durabilities, crystal growth velocities, specific ionic conductivities, refractive indices, Abbe numbers and optical transmissions. The samples were ion exchanged in a NaNO₃/AgNO₃ salt melt in order to determine the Na⁺/Ag⁺ interdiffusion coefficients and the refractive indices, Abbe numbers and optical transmissions of the ion exchanged silver containing glasses. Glasses doped with ZnO are advantageous for the production of gradient index lenses due to their improved chemical durability and smaller crystal growth velocities at viscosities in the range of 10⁵–10⁶ dPa s. The optical properties of these glasses are similar to those of glasses without RO.     

Synthesis and characterization of calcium phosphate based bioactive quaternary P2O5-CaO-Na2O-K2O glasses

Calcium phosphate based bioactive quaternary glass systems P₂O₅-CaO-Na₂O-K₂O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P₂O₅ at 47 mol% and CaO at 30.5 mol% and by varying the K₂O and Na₂O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K₂O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.     

A structural interpretation of B10 and B11 NMR spectra in sodium borate glasses

It is shown that the B¹⁰ spectra for sodium borate glasses are sensitive to the different structural groups in the glasses. Five boron sites are inferred from the data: two 4-coordinated sites and three 3-coordinated sites. The two 4-coordinated boron sites are identified as BO₄ units connected to all BO₃ units, and BO₄ units connected to one BO₄ unit and three BO₃ units. The three 3-coordinated boron sites are identified as BO₃ units connected to: (1) all BO₃ units; (2) a mixture of BO₃ and BO₄ units; and (3) all BO₄ units. These five sites can be interpreted in terms of Krogh-Moe's structural model of alkali borate glasses, wherein the fraction of each structural group can be determined for eight sodium borate glasses spanning the compositional range from 0 to 35 mol% Na₂O. The resulting fractions are consistent with Krogh-Moe's structural model.     

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.     

Anionic structure and elasticity of Na2O-MgO-SiO2 glasses

The structure and elastic properties of a series of xNa₂O · MgO · 4SiO₂ glasses have been studied using both Raman and Brillouin spectroscopy. Relative to Na₂O-SiO₂ glasses, the maximum abundance for phyllosilicate structural units in the present glasses shows a lag of 0.5 units in the number of non-bridging oxygen per silicon atom (NBO/Si). This phenomenon has been attributed to the decrease in the average coordination number of modifying cations due to the presence of Mg²⁺. It has also been found that the decomposition of both metasilicate and disilicate (dimerized SiO₄) anionic structural units in Na₂O-SiO₂ glasses are enhanced by the addition of MgO. However, the presence of Mg²⁺ does not cause a considerable effect on the decomposition of phyllosilicate structural unit. The acoustic data have revealed that both shear and Young’s moduli of the present glasses decrease with increasing NBO/Si (the variation in bulk modulus is reversed, however). The resistance to shear deformation for the anionic structural units in silicate glasses has been found to decrease in the following order: tectosilicate > phyllosilicate > metasilicate > disilicate > orthosilicate. The relative contribution of the various anionic structural units to the bulk modulus of a glass remains to be determined. The ideal mixing model using Makishima-Mackenzie’s relationship for predicting Young’s modulus is not applicable to the present glasses.     

Refractive index behavior in phosphate glass from the view point of B3+ and Al3+ coordination

Higher refractive index and higher Abbe value were obtained simultaneously at B₂O₃/Al₂O₃ = 1 in the system of 65P₂O₅–xAl₂O₃–(20 ? x)B₂O₃–10CaO–5Li₂O, although the refractive index generally shows a positive correlation with the dispersion. We investigated the molar volume and the molar refraction by Lorentz–Lorenz’s formula and also studied the coordination number of ¹¹B and ²⁷Al by MAS NMR. By the replacement of Al₂O₃ with B₂O₃, the molar refraction constantly decreased, but the molar volume was minimized at B₂O₃/Al₂O₃ = 1. The refractive index behavior of the glasses was mainly determined by the molar volume in the system. The coordination number of B³⁺ was only IV and it did not change if the composition was changed. On the other hand the coordinations IV, V and VI were observed for Al³⁺. The ratio of Al³⁺(VI) was maximized at B₂O₃/Al₂O₃ = 1. It is considered that the higher coordination of Al³⁺ brings the improvement of the packing and it leads to high refractive index.     

Structural analysis of Na2OGa2O3SiO2 glasses by the X-ray diffraction method

The structure of Na₂OGa₂O₃SiO₂ glasses of four different compositions containing up to 45 mol. % Ga₂O₃ has been determined by the X-ray diffraction method. The radial distribution function D(r) obtained indicates that Ga³⁺ ions are in fourfold coordination and GaO₄ tetrahedra are formed in these glasses. The reduced intensity function S·i(S) and radial distribution function D(r) which were calculated based on a structural model for A-25, 0.25(Ga₂O₃)·0.75(Na₂O·2SiO₂)/3 glass agreed well with the observed ones.     

Phase separation and crystallization in the system SiO2-Al2O3-P2O5-B2O3-Na2O glasses

The phase separation and crystallization behavior in the system (80 − X)SiO₂ · X(Al₂O₃ + P₂O₅) · 5B₂O₃ · 15Na₂O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al₂O₃-P₂O₅-SiO₂ and forms a continuous phase. Glasses containing a larger amount of Al₂O₃-P₂O₅ (X = 40 and 50) readily crystallize and precipitates tridymite type AlPO₄ crystals. It is estimated that the phase separation occurs forming continuous Al₂O₃-P₂O₅-SiO₂ phase at first, and then tridymite type AlPO₄ crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively.     

Infrared transmission of (R2O OR R’O)–(TiO2, Nb2O5 OR Ta2O5)-Al2O3 glasses

The new families of aluminate glasses obtained by the present authors from their melts in the systems K₂O–Ta₂O₅–Al₂O₃, Na₂O–K₂O–Ta₂O₅–Al₂O₃, K₂O –Cs₂O– Ta₂O₅–Al₂O₃, K₂O–Nb₂O₅–Al₂O₃, Na₂Oz.sbnd;K₂O–TiO₂–Al₂O₃, BaO–TiO₂–Al₂O₃, BaO–ZrO₂–TiO₂–Al₂O₃ and Na₂O–K₂O–BaO–ZrO₂–Ta₂O₅–TiO₂ –Al₂O₃ showed high transmissions of visible and infrared (IR) radiation ranging from 0.4 to about 6 μm, as well as high refractive indices up to 2.0. Their physical and chemical properties such as glass-forming ability, softening temperature, hardness and hygroscopicity were comparable to conventional silicate glasses. These properties are useful for IR applications. The cause of the high IR transmission of the aluminate glasses was interpreted in terms of the masses of the constituent cations and the single bond strengths of the cations with oxygen ions.     

Optical Properties of Bi2O3-TeO2-B2O3 Glasses

Glasses of the Bi₂O₃-TeO₂-B₂O₃ ternary system were developed and their linear and nonlinear optical properties were investigated. The absorption edges of these glasses were found to be 367-384 nm with a good transmittance in visible wavelength, although they exhibit the refractive indices as high as 1.98-2.12 at 633 nm. The absorption edges are quite steep and they are analyzed by the Urbach theory. The obtained Urbach energies of these glasses are 73-79 meV which are comparable to silica glasses. The high refractive index and its glass composition dependency are discussed according to the basics of the electronic polarizability and optical basicity. The high third order nonlinear susceptibility χ⁽³⁾ = 2.0 × 10^− 12 esu at 800 nm was also obtained in the 36Bi₂O₃-18TeO₂-46B₂O₃ glass.     

Glass formation in the Sb2O3-CdCl2-SrCl2 ternary system

Vitreous systems based on antimony oxide Sb₂O₃ have been investigated. The limits for glass formation are reported in the Sb₂O₃-CdCl₂-SrCl₂ ternary system, and in the Sb₂O₃-SrCl₂-(0.5CdCl₂ + 0.5ZnCl₂) pseudo ternary system. Amorphous state is confirmed by XRD patterns. Thermal measurements implemented by differential scanning calorimetry show that Tg is above 300 °C. As a general trend, Tg increases with chloride content. These glasses have an extended transmission in the mid-infrared spectrum with a refractive index larger than 2. The influence of the CdCl₂/Sb₂O₃ substitution on the physical properties has been studied in the (90 − x)Sb₂O₃-xCdCl₂-10SrCl₂ system: thermal expansion, Vickers microhardness, Young and bulk modulus decrease as cadmium concentration increases. An inverse dependence is observed for shear modulus. This behaviour is discussed in relation to structural hypothesis.     

Structural studies on boroaluminosilicate glasses

Two series of boroaluminosilicate glasses having varying mole ratios of B₂O₃/Na₂O (series 1) and B₂O₃/SiO₂ (series II) were prepared by conventional melt-quench method. Based on ²⁹Si and ¹¹B MAS NMR studies, it has been established that for series I glasses up to 15 mol% B₂O₃ content, Na₂O preferentially interacts with B₂O₃ structural units resulting in the conversion of BO₃ to BO₄ structural units. Above 15 mol% B₂O₃ for series I glasses and for all the investigated compositions of the series II glasses, silicon structural units are unaffected whereas boron exist in both trigonal and tetrahedral configurations. Variation of microhardness values of these glasses as a function of composition has been explained based on the change in the relative concentration of BO₄ and BO₃ structural units. These glasses in the powder form can act as efficient room temperature ion exchangers for metal ions like Cu²⁺. It is seen that the ion exchange does not affect the boron and silicon structural units as revealed by IR studies.