Changes In Glass Structure Research Articles

Tailoring the Mechanical Properties of Metaluminous Aluminosilicate Glasses by Phosphate Incorporation

The characterisation of aluminosilicate glasses is highly relevant in geosciences and for engineering applications such as reinforcement fibres or touchscreen covers. The incorporation of phosphate as a third network-forming species into these glasses offers unique opportunities for fine-tuning glass properties via changes in glass structure and polymerisation. In this work, we studied melt-quenched aluminosilicate glasses within the system SiO2-Al2O3-Na2O-P2O5 with 50 to 70 mol% SiO2 and up to 7.5 mol% P2O5. All glasses were metaluminous (Al:Na = 1) in order to maximise the degree of polymerisation. Increasing the phosphate content at the expense of NaAlO2 lead to reduced glass polymerisation and density, resulting in a decrease in elastic moduli and hardness and an increase in strain-rate sensitivity. When increasing the silica content by substituting SiO4 for AlO4 tetrahedra, network polymerisation remained mostly unchanged, as confirmed by nearly constant molar volume and hardness. Densification upon indentation was analysed by Raman spectroscopy and finite element analysis. We find that the elastic properties and hardness of metaluminous phospho-aluminosilicate glasses are governed by changes in density and network polymerisation. Other mechanical properties underlie more complex changes in glass structure.

Composition-structure-property modeling for Nd3+ doped alkali-phosphate laser glass

In the study of Nd:phosphate laser glass modified by introducing Li2O (0–8 mol%) and Na2O (0–8 mol%), respectively, glass transition temperature (Tg), thermal expansion coefficient (α), nonlinear refractive index (n2) and effective linewidth (Δλeff) were measured. Statistical based composition-structure-property (C-S-P) models were systematically developed. For the single-component study, a limitation of the C-P model approach is first discussed, i.e., which cannot adequately simulate glass property responses. To overcome the C-P mode limitation from the single-component study, C-S and S-P models were subsequently explored. The alternative methodology, transforms a problem of a given glass property response to a single (one dimensional) oxide change to a problem of the same property response to multi-directional glass structural changes for building a corresponding statistical S-P model. The same methodology is also applied to build C-S model. Plausible glass network structural units (or distributions) were derived from measured Fourier transform Infra-red (FTIR) spectra aided by using a standard curve-fitting method. As a result, S-P models showed significant improvements in simulating the measured glass properties. The C-S-P models, as a glass design tool box, were validated by using four designed glasses in the current independent design of experiment (DOE). For the four DOE derived glass compositions, the measured Li2O and Na2O concentrations and measured properties of the four glasses were very close to the C-S-P model predictions within the experimental errors, except for two cases where differences of Tg were significantly large.

Effect of ZrO2 crystallization on ion exchange properties in aluminosilicate glass

Ion exchange has the potential to improve the mechanical properties of glass ceramics. In this work, ZrO2 nanocrystals embedded transparent glass ceramics were prepared and effect of the crystallization on ion-exchange properties was investigated. The crystallization of ZrO2 did not affect the transmittance and Vickers hardness due to the small nanocrystal size and the low crystallinity, but significantly enhanced the ion exchange depth of layer (DOL). X-ray diffraction, high resolution transmission electron microscope, Raman spectra and nuclear magnetic resonance analysis demonstrated that with the crystallization of ZrO2, the charge compensator (Na+) was released, which promoted the transformation of highly coordinated Al into [AlO4]− tetrahedral units and the formation of Na+ balanced non-bridging oxygens. These changes in structure of glass made the Na+ more mobile and increased the DOL upon the crystallization. Results reported here may be useful for the development of glass-ceramic materials suitable for chemical strengthening.

Structural evolution of fused silica below the glass-transition temperature revealed by in-situ neutron total scattering

The common belief that glass structure is completely frozen-in at room temperature is challenged at both macroscopic and atomic scales. Here, we demonstrate an analytical method to elucidate the fine details of a continuous structural change of fused silica (FS) at temperatures below the glass-transition temperature using in-situ neutron total scattering. We find that the SiO4 tetrahedron expands through the entire temperature range with a local coefficient of thermal expansion of 9.1 × 10−6 K−1, while the average medium-range distance, derived from the first sharp diffraction peak of the structure factor, expands at a rate of 21 × 10−6 K−1. Such an expansion difference reflects glass-structure changes within the “rigid-unit mode” model, where each tetrahedron behaves as a rigid unit and the flexible rotations between rigid units lead to more than two times higher medium-range thermal expansion. We further demonstrate that such rotations change the shape of individual rings, leading to a measurable change in the first sharp diffraction peak (FSDP). This study paves the way to measure the structural changes of other silicate glasses, especially through the glass transition.

The effect of mixed La-Y doping on water resistance of phosphate glass

In this work, the effect of mixed La-Y doping on the water resistance of xLa2O3–(16-x)Y2O3–8Al2O3–10Na2O–66P2O5 (x = 0, 4, 8, 12, 16 mol%) glasses was studied. The glass structure, glass transition temperature (Tg), dc conductivity (σdc) and water resistance of glass were respectively characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), electrochemical workstation and water resistance test. The results show that with the gradual replacement of Y2O3 by La2O3, the value of Q(2) (Q2 content as a percentage of the sum of Q1 and Q2 contents in glass structure) and water resistance characterized by mass loss per unit surface area indicate strong “mixed rare earth effect”. It is obvious that the change of glass structure causes water resistance of glass to vary nonlinearly and exhibit a positive deviation from linearity. The results can provide some useful information for tailoring the chemical durability of glass by mixed rare earth doping.

The Nitrogen-Hole-Center Electron Transfer Imparts Reduction Ability to Eu Ion in AlN-Containing Phosphate Glasses

The europium ion possesses fascinating luminescent properties, and its oxidation state is largely governed by the interaction with doping matrixes due to the appropriate redox potential. Here, we unravel the connection between the phosphate oxynitride glass structure and stepwise valence changes from Eu3+ to Eu2+. Through tuning the introducing content of AlN in phosphate glasses, an effective reduction among Eu3+ ions could be readily realized. This reduction process is explained by the “Nitrogen-Hole-Center (NHC) electron transfer” model. In this model, NHC and Eu3+ ions play as electron donor and acceptor roles, respectively. Under continuous thermal vibration of the lattice, the electrons released from unstable NHC could be caught by their nearest neighbor Eu3+ ions. Moreover, nitrogen-to-oxygen substitution significantly enhances the covalency and rigidity of the glassy network by forming distorted [PO3N] and [PO2N2] tetrahedrons, creating a perfect shield for Eu2+ and resisting the attack of oxygen.

Microscopic Description of Yielding in Glass Based on Persistent Homology

Persistent homology (PH) was applied to probe the structural changes of glasses under shear. PH associates each local atomistic structure in an atomistic configuration to a geometric object, namely, a hole, and evaluates the robustness of these holes against noise. We found that the microscopic structures were qualitatively different before and after yielding. The structures before yielding contained robust holes, the number of which decreased after yielding. We also observed that the structures after yielding approached those of quickly quenched glass. This work demonstrates the crucial role of robust holes in yielding and provides an interpretation based on geometry.

Correlation between glass transition effect and structural changes in multicomponent iron phosphate-silicate glasses

Iron phosphate-silicate glasses from P2O5–SiO2–K2O–MgO–CaO–Fe2O3 system were subjected to the thermal and spectroscopic studies in order to gain information about their structure and thermal behavior in the range of glass transition effect. Research includes results obtained via DSC, MIR and DRIFT spectroscopy. Designated values of glass transition temperature and specific heat change slightly increases with Fe2O3 incorporation. Spectra collected during thermal treatment of glasses containing 2 and 30 mol% Fe2O3 exhibited various changes. Fe2O3 addition affected the glass structure by its reinforcement and led to its preservation during thermal treatment. The connection between density, molar volume, oxygen packing density and the chemical composition’s alteration were also established because of the direct dependence of physical properties and the structure. Obtained results supported thermal and spectroscopic studies. Conducted research is considered as a contribution to the knowledge about the family of iron phosphate glasses, which are known from their interesting properties and widely used applications.

Synthesis and structural characterization of a new SbPO4-GeO2 glass system

This work presents the production and characterization of a new prolific binary glass system based on SbPO4-GeO2. The dependence of GeO2 content on thermal, structural and optical properties were investigated by means of thermal analysis, Raman, UV–Vis-NIR, infrared, M-lines and EPR spectroscopy. Glass transition temperatures remain constant around 410 °C when GeO2 content is increased, indicating that GeO4 units are not responsible for increasing the connectivity of PO4 units. Thermal stability linearly increases as a function of GeO2 content, reaching a value around 400 °C for glass containing 90 mol% of GeO2. Raman spectroscopy was used to evaluate the glass structural changes when GeO2 is incorporated from 30 to 90 mol% indicating a gradual change from a phosphate to a germanate glass skeleton. The optical window extends from 350 nm at UV region, up to 2.7 μm in the middle-infrared region limited by the multiphonon cut-off due to the strong OH absorption. M-lines technique shows that increasing GeO2 content decreases the refractive index, mainly because the lower concentration of higher polarizable antimony atoms. EPR spectra of heat treated V2O5 doped glasses, at different temperatures above the glass transition temperature, shows the characteristic eight-line hyperfine splitting spectrum. The spin Hamiltonian parameters obtained from the simulated spectra indicates that the paramagnetic tetravalent vanadium ions in the glasses exist as vanadyl form VO2+, located in axially distorted octahedral sites. For glasses treated at higher temperatures a second VO2+ component appears in the EPR spectra and the analysis of the spin-Hamiltonian parameters suggests that these vanadyl ions are in more tetragonal distorted octahedral sites than those in the glass.

Study of the Structure of Iron-Containing Zinc Borate Glass

The results of the experimental study of glass of the xFe2O3–(100–x)[40ZnO. 60B2O3] composition in which the content of iron oxide varies from 0 to 10 mol % are presented. The regularities of the glass structure change in the short- and intermediate-range order structures are considered based on the data of infrared spectroscopy and Raman spectroscopy. The valence and coordination state of iron in a glass matrix is studied by Mossbauer spectroscopy.

Structural and Dielectric Studies on Na2O-PbO-SiO2 Glasses

Structural studies on x Na2O.(50-x)PbO.50SiO2 glasses have been carried out by different spectroscopic techniques. FTIR, EDX, NMR and dielectric spectroscopies are applied to follow the change in glass structure in terms of bridging oxygen (BO), non-bridging oxygen (NBO), and cluster species upon adding of Na2O at expense of PbO. NBOs are formed in the silicate network upon Na2O addition, since Na2O plays the role of glass modifier. Changes in relative area of Q2 (obtained from IR analysis) and NMR chemical shift of silicon nuclei with increasing Na2O are indicative for formation of the less shielded silicate units. While in sodium rich silicate glasses, the structural role of Na2O is changed due to changing Na coordination. FTIR analysis could be used to elucidate the changes related to changing the role of Na2O. The data obtained are correlated with that obtained from EDX spectroscopy. Moreover, the role of Na2O on the process of cluster formation when it substitutes PbO is determined. NBOs only are formed in the silicate network upon Na2O addition up to 30 mol%. On the other hand, in sodium rich silicate glasses an additional type of oxygen (free oxygen O2−) is present. The free oxygen is required for sodium to form aggregated cluster, specially at high concentration of Na2O (50 mol%). An increase in Na2O concentration in Na2O-rich silicate network results in increasing Na coordination instead of breaking more silicon–oxygen bonds. Scanning electron micrographs (SEM) and EDS spectroscopy in correlation with FTIR results confirm the presence of Na cluster species. The effect of clusters formation on AC conductivity was discussed according to jump relaxation model. Some parameters related to AC conductivity are found to be affected by the presence of cluster species in the glass network.

Effect of replacement of Al2O3 by Y2O3 on the structure and properties of alkali-free boro-aluminosilicate glass

Alkali-free boro-aluminosilicate glasses were prepared by the melt quenching method. The effect of Al2O3 replaced by different contents of Y2O3 on the structure and various properties of alkali-free boro-aluminosilicate glasses was studied. The changes of glass structure with varying components were investigated by the Fourier transform infrared spectra. Simultaneously, the relationship between the glass structure and the coefficient of thermal expansion, density, vickers hardness, bending strength, glass transmittance and chemical stability was discussed. The results show that the coefficient of thermal expansion and the density of glass increase with the increase of Y2O3 content. While, the chemical stability of the glass is reduced. The vickers hardness and bending strength decrease first and then increase with the Y2O3 content increasing. All the glasses have excellent optical transmittance, reaching more than 85%.

Features of changes in the surface structure of K-208 glass under electron—proton irradiation

Changes in the surface structure of K-208 glass after single-time irradiation of its samples with 20-keV electrons and protons are studied using atomic-force microscopy. Irradiation is performed in a vacuum chamber under a pressure of 10–4 Pa; the densities of the electron (ϕ e ) and proton (ϕ р ) fluxes are varied in the range of 1010–2.5 × 1011 cm−2 s−1. Analysis of the samples irradiated in the case where the parameters ϕ e and ϕ р increased in a stepwise manner makes it possible to study the appearance, growth, and evolution of microscopic structures on their surfaces. The radiation-stimulated processes of defect annealing and the release and field diffusion of alkali metal ions are accompanied by crystallization of the irradiated glass layer, which gives grounds for the use of dislocation mechanisms for mass transfer in explaining the formation of microprotrusions on its surface. It is shown that the character of changes in the structure is determined by the values of the parameters ϕ e and ϕ р and the ratio between them. In particular, it is established that, in the case of electron— proton irradiation of the glass, electrostatic discharges begin to noticeably affect the formation of microprotrusions for ϕ е > 3ϕ р .

The role of different network modifying cations on the speciation of the Co2 + complex in silicates and implication in the investigation of historical glasses

In the last decades the speciation of the cobalt complex in a glass matrix has been extensively studied. Bivalent cobalt ions in glasses of different composition commonly adopt a tetrahedral coordination, though hexa- or penta-coordinated species are also possible. Changes in the absorbance spectrum of Co-doped glasses were attested in previous studies according to the introduction of different modifying cations. A shifting of the first sub-band characterizing the typical triplets of tetrahedral Co2+ ions in both the visible and near infrared regions was observed, but discrepancies in literature suggested a relevant role of glass composition on the definition of the optical signature of cobalt. Co-doped glasses with different composition (soda-lime, potash-lime, mixed alkali and ZnO-Na2O-CaO-SiO2) were studied via Fiber Optic Reflectance Spectroscopy (FORS). Pseudo-Voigt functions were used for the deconvolution of the absorbance spectra and the features of the bands characteristic of each cobalt complex were investigated. The structural role played by each modifying cation and the fundamental implications of glass basicity on the speciation of different Co-complexes were stressed. Changes in glass structure resulted in different equilibria between the three absorbing species whose specific optical signatures in the 480–530nm region interact to determine the resulting absorbance spectrum.

Polarizability, optical basicity and electric susceptibility of Er3 + doped silicate borotellurite glasses

Glasses system was fabricated using the chemical composition {[(TeO2)0.7 (B2O3)0.3]0.8 (SiO2)0.2}1−x (Er2O3)x with x=0.01, 0.02, 0.03, 0.04 and 0.05 by melt-quenching method. The glasses were subjected to FTIR and XRD to study the glass structural changes and amorphous nature respectively. The absorption spectrum of the glasses were obtained from UV–Vis spectroscopy and used to calculate the energy band gap. Using the Archimedes principle, the density and the molar volume were determined. From the density, molar volume, and energy band gap, other parameters such as refractive index, molar refractive index, metallization criterion, reflection loss, transmission coefficient, polarizability, optical basicity, polaron radius, dielectric constant, optical dielectric constant, electric susceptibility, average electronegativity and others parameters were obtained by calculation. The polarizability values and the optical basicity were found to increase with Er3+ ions concentration increase. The dielectric constant, optical dielectric constant and the linear electric susceptibility decreased with increase in Er3+ ions concentration. The properties studied for the erbium doped glass system suggest the glass system has a potential in the EDFA application.

Effect of gamma irradiation on X-ray absorption andphotoelectron spectroscopy of Nd-doped phosphate glass.

X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) of Nd-doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L3-edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy-dispersive X-ray spectroscopy measurements. The ratio of non-bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.

Investigation of gamma radiation induced changes in local structure of borosilicate glass by TDPAC and EXAFS

Gamma radiation induced changes in local structure around the probe atom (Hafnium) were investigated in sodium barium borosilicate (NBS) glass, used for immobilization of high level liquid waste generated from the reprocessing plant at Trombay, Mumbai. The (NBS) glass was doped with 181Hf as a probe for time differential perturbed angular correlation (TDPAC) spectroscopy studies, while for studies using extended X-ray absorption fine structure (EXAFS) spectroscopy, the same was doped with 0.5 and 2 % (mole %) hafnium oxide. The irradiated as well as un-irradiated glass samples were studied by TDPAC and EXAFS techniques to obtain information about the changes (if any) around the probe atom due to gamma irradiation. TDPAC spectra of unirradiated and irradiated glasses were similar and reminescent of amorphous materials, indicating negligible effect of gamma radiation on the microstructure around Hafnium probe atom, though the quaqdrupole interaction frequency (ω Q) and asymmetry parameter (η) did show a marginal decrease in the irradiated glass compared to that in the unirradiated glass. EXAFS measurements showed a slight decrease in the Hf-O bond distance upon gamma irradiation of Hf doped NBS glass indicating densification of the glass matrix, while the cordination number around hafnium remains unchanged.

Effect of the Al2O3 addition on the formation of silver nanoparticles in heat treated soda-lime silicate glasses

We investigate the formation and evolution of silver nanoparticles in the non-irradiated thermally treated glass system Ag:(37–x)Na2O–10CaO–xAl2O3–53SiO2mol%, where x=0.0, 0.5, 1, 2 and 5, doped with 0.2mol% AgNO3. Using optical absorption and transmission electron microscopy we studied the effect of the gradual addition of Al2O3 to the chemical composition of the soda aluminosilicate glasses. A quantitative method for the evaluation of the relative nanoparticles concentration, proportional to the optical absorption intensity of the silver Surface Plasmon Resonance band, was developed and applied to the study of the behavior of the number of particles precipitated in samples thermally treated at temperatures of 400, 500, and 600°C. Three mechanisms were found, as consequence of the substitution of SiO4 by AlO4 glass forming local tetrahedral structural units, resulting in the gradual suppression of the negatively charged NBOs−, which are the only reducing sources available in the present non-irradiated glass system. The effects produced by the glass chemical and structural changes on the Ag nanoparticles production are discussed.

Micro-structuring the surface reactivity of a borosilicate glass via thermal poling

Thermal poling was proven successful to induce second order nonlinear properties and concurrent modification of composition, structure and chemical reactivity in glasses. With current efforts to reduce devices sizes in components employing such attributes, means to control changes at the micrometer scale are needed. We present a micro-imprinting poling process to locally tailor surface properties of a glass. Measurements using infrared, Raman and second harmonic generation microscopies confirm that changes in glass structure associated with an induced static electric field are responsible for the enhanced surface reactivity that is successfully controlled at the micrometer scale.

Influence of heat treatment for electrical response and a Raman spectroscopic investigation in CaO[sbnd]TiO2[sbnd]xSiO2 glasses

The heat treatment-dependent Raman spectra and complex electrical impedance for the CaOTiO2xSiO2 (CTSO; x = 0.5, 1 and 2) glasses were measured. We investigate the influence of different compositions in CTSO systems on the dielectric and electrical properties with respect to the oxygen-vacancy-related frequencies of 600 Hz ≤ ω ≤ 100 MHz and from room temperature to 600 °C. The observed Raman spectra of as-quenched CTSO glasses are almost identical with these 6 cycles heat-treated samples in the whole range of bands. Impedance measurement shows that the oxygen vacancies remain during the heat treatment for these glasses. We discuss the origin of oxygen vacancy and its role for the electrical conductivity. The dc electrical activation energies Edc for all CTSO glasses are found to be the same as ∼0.83 eV, indicating that dc electrical conduction in bulk does not dependent on changes in glass structure. The dielectric relaxation time for CTSO (x = 0.5) glass is short compared to that of CTSO (x = 1 and 2) glasses.