Preparation and characterization of glasses in the Ag2S + B2S3 + GeS2 system

The glass forming range of the Ag₂S + B₂S₃ + GeS₂ ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag-B-Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS_4/2 and AgBS_4/2, and trigonal units, BS_3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS_3/2 and Ag₃B₃S₃S_3/2 six membered rings, are also observed in these glasses at higher Ag₂S modification levels because the further addition of Ag₂S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag₂S goes into the GeS₂ subnetwork to form Ag₃S₃GeS_1/2 groups before going to the B₂S₃ subnetwork. In doing so, it is suggested that B₁₀S₂₀ supertetrahedra exist in Ag₂S + B₂S₃ and Ag₂S + B₂S₃ + GeS₂ glasses. Significantly B-S-Ge bonds form in the B₂S₃ + GeS₂ glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.     

The comparative structure, properties, and ionic conductivity of LiI + Li2S + GeS2 glasses doped with Ga2S3 and La2S3

The well known and characterized fast ion conducting (FIC) LiI + Li₂S + GeS₂ glass-forming system has been further optimized for higher ionic conductivity and improved thermal and chemical stability required for next generation solid electrolyte applications by doping with Ga₂S₃ and La₂S₃. These trivalent dopants are expected to eliminate terminal and non-bridging sulfur (NBS) anions thereby increasing the network connectivity while at the same time increasing the Li⁺ ion conductivity by creating lower basicity [(Ga or La)S_4/2]⁻ anion sites. Consistent with the finding that the glass-forming range for the Ga₂S₃ doped compositions is larger than that for the La₂S₃ compositions, the addition of Ga₂S₃ is found to eliminate NBS units to create bridging sulfur (BS) units that not only gives an improvement to the thermal stability, but also maintains and in some cases increases the ionic conductivity. The compositions with the highest Ga₂S₃ content showed the highest T_gs of ∼325 °C. The addition of La₂S₃ to the base glasses, by comparison, is found to create NBS by forming high coordination octahedral LaS₆³⁻ sites, but yet still improved the chemical stability of the glass in dry air and retained its high ionic conductivity and thermal stability. Significantly, at comparable concentrations of Li₂S and Ga₂S₃ or La₂S₃, the La₂S₃-doped glasses showed the higher conductivities. The addition of the LiI to the glass compositions not only improved the glass-forming ability of the compositions, but also increased the ionic conductivity glasses. LiI concentrations from 0 to 40 mol% improved the conductivities of the Ga₂S₃ glasses from ∼10⁻⁵ to ∼10⁻³ (Ω cm)⁻¹ and of the La₂S₃ glasses from ∼10⁻⁴ to ∼10⁻³ (Ω cm)⁻¹ at room temperature. A maximum conductivity of ∼10⁻³ (Ω cm)⁻¹ at room temperature was observed for all of the glasses and this value is comparable to some of the best Li ion conductors in a sulfide glass system. Yet these new compositions are markedly more thermally and chemically stable than most Li⁺ ion conducting sulfide glasses. LiI additions decreased the T_gs and T_cs of the glasses, but increased the stability towards crystallization (T_c − T_g).     

Three-dimensional structure of fast ion conducting 0.5Li2S + 0.5[(1 − x)GeS2 + xGeO2] glasses from high-energy X-ray diffraction and reverse Monte Carlo simulations

A high-energy X-ray diffraction study has been carried out on a series of 0.5Li₂S + 0.5[(1 − x)GeS₂ + xGeO₂] glasses with x = 0.0, 0.1, 0.2, 0.4, 0.6 and 0.8. Structure factors were measured to wave vectors as high as 30 Å⁻¹ resulting in atomic pair distribution functions with high real space resolution. The three dimensional atomic-scale structure of the glasses was modeled by reverse Monte Carlo simulations based on the diffraction data. Results from the simulations show that at the atomic-scale 0.5Li₂S + 0.5[(1 − x)GeS₂ + xGeO₂] glasses may be viewed as an assembly of independent chains of (Li^+-S)₂GeS_2/2 and (Li^+-O)₂GeO_2/2 tetrahedra as repeat units, where the Li ions occupy the open space between the chains. The new structure data may help understand the reasons for the sharp maximum in the Li⁺ ion conductivity at x ∼ 0.2.     

Studies of some mechanical and optical properties of: (70 − x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Specimens of the glassy system: (70 − x)TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by the melt-quenching. An ultrasonic pulse-echo technique was employed, at 5 MHz, for measuring: the ultrasonic attenuation, longitudinal and shear wave velocities, elastic moduli, Poisson ratio, Debye temperature and hardness of the present glasses. It is found that the gradual replacement of TeO₂ by Li₂O in the glass matrix up to 30 mol% leads to decrease the average crosslink density and rigidity of prepared samples which affects the properties, i.e., the hardness, ultrasonic wave velocities and elastic moduli are decreased, while the Poisson ratio and the ultrasonic attenuation are increased. Also, optical absorption spectra were recorded in the range, 200-800 nm for these glasses. The obtained results showed that a gradual shift in the fundamental absorption edge toward longer wavelengths occurred. Values of both of the optical energy gap, E_opt, and width tails, ΔE, are determined. It is observed that E_opt is decreased and ΔE increased with the increase of Li₂O in the glass matrix up to 30 mol%. The compositional dependences of the above properties are discussed and correlated to the structure of tested glasses.     

The glass transition temperature and infrared absorption spectra of: (70−x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Glasses of the system: (70−x) TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (T_g) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO₂ by Li₂O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm⁻¹. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.     

RDF analysis, positron annihilation and Raman spectroscopy of xTiO2-(60 − x)SiO2-40Na2O non-linear optical glasses: III. Non-bridging oxygen bonds tracing and structure analysis

xTiO₂-(60 − x)SiO₂-40Na₂O glasses have proven an interesting linear and non-linear optical properties [M. Abdel-Baki, F. Abdel Wahab, F. El-Diasty, Mater. Chem. Phys. 96 (2006) 201]. The investigated glasses show one order of magnitude enhancement for the second-order index of refraction and third-order optical susceptibility over some TiO₂ silicate glasses. In this work, we continue studying these glasses using three different techniques to analyze the glass structures seeking to provide a deep insight for the relation between structure, compositions and the optical characteristics of these glasses. Radial Distribution Function analysis (RDF) combined Raman spectroscopy are used to study these glasses. Positron annihilation lifetime spectroscopy and Doppler broadening measurements are carried out to investigate the change in the glass structure as the incorporation of TiO₂ concentration into glass. The origin of the non-bridging oxygen (NBO) bonds has been traced to correlate their existence with the measured non-linear optical properties of the investigated glasses.     

The structure and optical properties of GeO2-GeS2 glasses

Oxy-chalcogenide glasses with compositions of xGeO₂-(100 − x)GeS₂, where 0 ? x ? 100 mol%, have been prepared and studied in terms of their structures and optical properties. X-ray fluorescence spectroscopy shows that Ge:S ratio can deviate from GeS₂ by ∼10 at.%, depending critically upon the preparation conditions. Raman scattering spectroscopy suggests that stoichiometric GeO₂-GeS₂ glasses have a heterogeneous structure in the scale of 1-100 nm. The optical gaps are nearly constant at 3.0-3.5 eV for glasses with 0 ? x ? 80 mol% and abruptly increase to ∼6 eV in GeO₂. This dependence suggests that the optical gap is governed by GeS₂ clusters, which are isolated and/or percolated. Composition-deviated glasses appear as orange and brown, and these glasses seem to have more inhomogeneous structures.     

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.     

Glass formation, physico-chemical properties, and structure of glasses based on Ga2S3-GeS2-Sb2S3 system

We prepared sulfide glasses based on a Ga₂S₃-GeS₂-Sb₂S₃ system and investigated the compositional dependences of their physico-chemical properties and structure. Additivities were observed for density and refractive index; i.e., these properties were presented by the summation of the contribution from each component. With the increase of Sb₂S₃ content, the density, refractive index, and thermal expansion coefficient increased while the glass transition and softening temperatures decreased, and the short-wavelength absorption edge shifted to the longer wavelength side. These variations are expected from the incorporation of a heavy element (Sb) into the glasses. On the other hand, the replacement of GeS₂ by Ga₂S₃ increased the density and refractive index, and shifted the short-wavelength absorption edge to the longer wavelength side. These variations were explained by the increase of the number densities of the cations with the replacement and the formation of metal-metal bonds. The latter was confirmed from the Raman spectra. We also investigated the effects of Ag₂S incorporation on the optical properties. The incorporation of Ag₂S increased the density and refractive index whereas the position of the short-wavelength absorption edge varied little. These results show the possibility of fabricating an optical waveguide by Ag incorporation into the glasses.     

Spectroscopic properties of Er-doped xGeO2-(80 − x)TeO2-10ZnO-10BaO glasses

Erbium-doped glasses with composition xGeO₂-(80 − x)TeO₂-10ZnO-10BaO were prepared by melt-quenching technique. The phonon sideband spectra and the optical absorption band edges for the host matrix were confirmed by means of the spectral measurements. Standard Judd-Ofelt calculations have been completed to these glasses. The dependence of up-conversion and infrared emission under 980 nm excitation on the glass composition was studied. The quantum efficiencies for the ⁴I_13/2 → ⁴I_15/2 transition of trivalent erbium in the glasses were estimated.     

Glass formation in and structural investigation of Li2S + GeS2 + GeO2 composition using Raman and IR spectroscopy

Li₂S + GeS₂ + GeO₂ ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO₂ concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S⁻) sulfurs are observed in Raman and IR spectra of binary Li₂S + GeS₂ glasses. Additions of GeO₂ to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S⁻) remain constant in intensity up to high GeO₂ concentrations. At higher concentrations of GeO₂ (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO₂ concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge⁴⁺ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li₂S + GeS₂ + GeO₂ glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.     

Effect of pressure on the refractive index and relative density of the CaO · Al2O3 · 6SiO2 glass

The refractive index for glass of the CaO · Al₂O₃ · хSiO₂ system with х = 6 in the range of pressures up to 6.0 GPa was measured using a polarization-interference microscope and an apparatus with diamond anvils. The changes in the relative density characterizing the compressibility of glass were estimated from the measured refractive indices within the framework of the theory of photoelasticity. The data were compared with the previous data for glasses of the same system with х = 2 and 4. The most compressible of the three glasses in the range 2.0-6.0 GPa was the CaO · Al₂O₃ · 6SiO₂ glass. For glasses with х = 2, 4 and 6 we calculated the degrees of polymerization of silicon-aluminum-oxygen network, NBO/T (NBO - non-bridging oxygen), which are determined as the ratio of the number of gram-ions of non-bridging oxygen atoms to the total number of gram-ions of network formers. The structure-chemical parameter NBO/T was calculated with due regard for the formation of triclusters and highly coordinated aluminum. The degree of polymerization of the CaO · Al₂O₃ · хSiO₂ glasses increases with increasing х, which agrees with the change of their relative density under pressure.     

Effect of P2O5 content in two series of soda lime phosphosilicate glasses on structure and properties - Part I: NMR

The effect of the variation in phosphate (P₂O₅) content on the structure of two series of bioactive glasses in the quaternary system SiO₂-Na₂O-CaO-P₂O₅ was studied. The first series (I) was a simple substitution of P₂O₅ for SiO₂ keeping the Na₂O:CaO ratio fixed (1.00:0.87). The second series was designed to ensure charge neutrality in the orthophosphate , therefore as P₂O₅ was added the Na₂O and CaO content was varied to provide sufficient Na⁺ and Ca²⁺ cations to charge balance the orthophosphate present. The glass network connectivity (NC) was calculated for each glass and a modification for the presence of a separate P₂O₅ phase was included (NC′). ³¹P and ²⁹Si magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was performed on glass series I and II to determine the structural units present and their relation to glass properties. ³¹P MAS-NMR spectra of series I resulted in a broad resonance around 9 ppm corresponding to orthophosphate in an amorphous environment. The 9.25 mol% P₂O₅ glass shown to be partially crystalline by X-ray diffraction was heat treated, and the ³¹P MAS-NMR spectrum showed a sharp peak around 3 ppm corresponding to calcium orthophosphate or sodium pyrophosphate and overlapping broader peaks at 8.5, 10.5 and 14 ppm possibly corresponding to two mixed calcium-sodium orthophosphate phases and amorphous sodium orthophosphate respectively. ³¹P MAS-NMR spectra of series II resulted in a broad resonance around 10.5 ppm corresponding to orthophosphate in an amorphous environment. ²⁹Si MAS-NMR spectra of glasses from series I showed a shift in the resonance peak from around −78 to −86 ppm indicating an increase in Q³ species in the glass and a reduction in Q² with phosphate addition confirming the presence of orthophosphate. The heat treated sample showed a sharp ²⁹Si-NMR resonance at −88 ppm, indicating a crystalline Q² six-membered combeite (Na₂O · 2CaO · 3SiO₂) silicate-type phase, which was confirmed by powder X-ray diffraction. ²⁹Si MAS-NMR spectra of glasses from series II showed no shift in the resonance at around −78 ppm across the series, confirming an orthophosphate environment.     

Vibrational modes and structure of (AgI)x (GeS1.5)100−x chalcohalide glasses

We report a structural investigation of bulk Ge-rich Ge–S–AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI)_x (GeS_1.5)_100−x (0  x_AgI  20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS_1.5 Raman spectrum is compatible with a glass structure composed of corner- and edge-sharing mixed GeS_nGe_4−n (n = 0–4) tetrahedra where units with n = 2–4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS₂ glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeS_nI_4−n or GeS_nGe_mI_4-n−m tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge–I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge–S network structure.     

Structure and properties of lithium thio-boro-germanate glasses

Structural studies of the ternary xLi₂S + (1 − x)[0.5B₂S₃ + 0.5GeS₂] glasses using IR, Raman, and ¹¹B NMR show that the Li₂S is not shared proportionately between the GeS₂ and B₂S₃ sub-networks of the glass. The IR spectra indicate that the B₂S₃ glass network is under-doped in comparison to the corresponding composition in the xLi₂S + (1 − x)B₂S₃ binary system. Additionally, the Raman spectra show that the GeS₂ glass network is over-modified. Surprisingly, however, the ¹¹Boron static NMR gives evidence that ∼80% of the boron atoms are in tetrahedral coordinated. A super macro tetrahedron, B₁₀S₁₈⁻⁶ is proposed as one of the structures in these glasses in which can account for the apparent low fraction of Li₂S present in the B₂S₃ sub-network while at the same time enabling the high fraction of tetrahedral borons in the glass.     

Dielectric analysis of tungsten-phosphoniobate 20A2O-30WO3 -10Nb2O5 -40P2O5 (A = Li, Na) glass-ceramics

New phosphate glasses of the quaternary system A₂O-Nb₂O₅-WO₃-P₂O₅, where X = Li and Na were prepared by the melt-quenching method. The introduction of WO₃ in the glass composition was based on the proposal of analysing the effect of the diminishing of the molar amount of the alkaline oxide and thus decreasing the molar ratio between network modifiers and network formers (M/F).In the present work we present the preparation of 20A₂O-30WO₃-10Nb₂O₅-40P₂O₅ (A = Li, Na) transparent glasses. These glasses were heat-treated in air, at 550 °C and 650 °C for 4 h. The structure of the obtained samples was studied by X-ray powder diffraction (XRD) and Raman spectroscopy and the morphology by scanning electron microscopy (SEM). The dc (σ_dc), ac (σ_ac) conductivity and dielectric spectroscopy measurements were performed in the function of the temperature and were related with the structural changes of the glass structures.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

Electrical transport properties of 0.5Li2O-0.5M2O-2B2O3 (M = Li, Na and K) glasses

Transparent glasses in the system 0.5Li₂O-0.5M₂O-2B₂O₃ (M = Li, Na and K) were fabricated via the conventional melt quenching technique. The amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz-10 MHz frequency range. The imaginary part of the electric modulus spectra was modeled using an approximate solution of Kohrausch-Williams-Watts relation. The stretching exponent, β, was found to be temperature independent for 0.5Li₂O-0.5Na₂O-2B₂O₃ (LNBO) glasses. The activation energy associated with DC conduction was found to be higher (1.25 eV) for 0.5Li₂O-0.5K₂O-2B₂O₃ (LKBO) glasses than that of the other glass systems under study. This is attributed to the mixed cation effect.     

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.     

Bioactive glasses in the system CaO-B2O3-P2O5: Preparation, structural study and in vitro evaluation

Glasses in the system x B₂O₃(1 − x) [y CaO P₂O₅], (x = 0, 0.1, 0.2, 0.3, y = 2, 2.6, 3, 4, 5) have been prepared by fast quenching of high temperature melts. The presence of B₂O₃ affected the glass forming ability, allowing the preparation of calcium phosphate glasses with y ? 2.6. The structure of glasses was analyzed by μ-Raman and infrared spectroscopy. The analysis indicated that the glass network is dominated by highly charged species from phosphate tetrahedra with 3 (pyro) or 4 (ortho) NBOs, while the boron atoms are incorporated mainly in 3 coordinated sites in the form of B∅₃ or B∅₂O⁻ units. A small fraction of units was also evident from the spectra analysis of glasses with high CaO content. All calcium borophosphate glasses exhibited bioactivity after soaking in SBF solution within a few days. This was observed by μ-Raman and SEM microscopy, while XRD patterns clearly revealed growth of hydroxyapatite phase. The presence of boron in the glass network has a catalytic effect at favoring bioactivity of the otherwise bioinert calcium phosphate glasses.