Structure Of Silicate Glasses Research Articles

The structure of sodium silicate glass from neutron diffraction and modeling of oxygen‐oxygen correlations

AbstractIt is shown that modeling the first oxygen‐oxygen peak in the neutron correlation function of a glass enables structural information about other correlations to be obtained, and the method is illustrated by application to a sodium silicate glass. The first O–O coordination number can be calculated from network theory, and sodium silicate crystal structures show that the mean O–O distance can be calculated from the Si–O distance, despite the distortion of the SiO4 tetrahedra. Modeling the O–O peak for a sodium silicate glass allows the Na‐O bond length distribution to be determined. For a binary glass with 42.5 mol% Na2O, it is found that the Na–O coordination number is 4.8(2) with an average bond length of 2.45 Å, and the Na–O bond lengths are more widely distributed than in sodium silicate crystal structures. Sodium ions are bonded mostly to non‐bridging oxygens (NBOs), and the Na–NBO coordination number may be four as in crystals. Sodium ions are also bonded to a smaller number of bridging oxygens (BOs). Contrary to previous reports, it is not concluded that Na–NBO bonds are shorter than Na–BO bonds, but instead that the Na–BO distribution is relatively narrow, whilst the Na–NBO distribution extends to both shorter and longer distance. The broad distribution of Na–O bond lengths arises from a relatively broad distribution of Na–NBO bond valences, subject to the overall requirement of charge balance.

Effect of Vanadium Oxide on the Structure and Li-Ion Conductivity of Lithium Silicate Glasses

The commercially ubiquitous liquid electrolytes for lithium-ion batteries have several shortcomings in terms of safety. Therefore, development of solid electrolytes, especially those that are glass-based, has been gaining increasing interest in recent times. However, the fundamental understanding of the changes in the glass structure and the corresponding changes in the properties due to the addition of dopants is necessary for the development of glasses. Therefore, here, we report a study on the role of vanadium on the glass structure, ionic conduction, crystallization behavior, and other properties of lithium silicate-based glasses (23Li2O–2.64K2O–2.64Al2O3–71.72SiO2) as a solid electrolyte for high-temperature Li-ion battery applications. Furthermore, we proposed a mathematical model to describe/quantify the ion-conducting channels’ connectivity in glasses. The experimental glass structures were assessed using 29Si, 51V, 27Al nuclear magnetic resonance, Fourier transform infrared, and ultraviolet–visible spectroscopy techniques. The ionic conductivity was measured by impedance spectroscopy, and the crystallization behavior was studied by optical microscopy and X-ray diffraction. Furthermore, molecular dynamics simulations were also used to gain structural insights of the glasses. In the designed compositions, the addition of vanadium decreased the overall concentration of Li+ ions. However, the results revealed that the ionic conductivity improved with the addition of vanadium in spite of a decrease in the number of charge carriers. This suggests that vanadium makes the pathways easier for the conducting ions. Thus, we conclude that vanadium modifies the conduction channels to promote better hoping of the ions from one site to another.

Role of vanadium oxide on the lithium silicate glass structure and properties

AbstractThe structural role of V in 28Li2O–72SiO2 (in mol%) lithium silicate glass doped with 0.5 mol% V2O5 was assessed using 29Si and 51V Nuclear Magnetic Resonance (NMR), Fourier‐transform infrared (FTIR), and X‐ray photoelectron (XPS) spectroscopy techniques. Despite the low amount of V2O5 used, the structural information obtained or deduced from the statistical analysis of the NMR data could explain the evolution of glass properties after V2O5 addition. The XPS results indicated that all vanadium exists in 5+ oxidation state. Both the 29Si NMR and FTIR data point toward an increase in the polymerization of the silicate network, caused by the V2O5 acting as network former, capable to form various tetrahedral units (for n = 0, 1, and 2) in the glasses. These units, which are similar to phosphate units, scavenge the Li+ ions and cause the silicate network to polymerize. However, in an overall balance, the entire glass network is depolymerized due to the additional nonbridging oxygens contributed by the vanadium polyhedra. The addition of vanadium causes the network to expand and increases the ionic conductivity.

Mixed Alkali Effect in Silicate Glass Structure: Viewpoint of 29Si Nuclear Magnetic Resonance and Statistical Mechanics

The mixed alkali effect in glasses is the deviation from linear property changes when alkali cations are mixed. The extent of this effect and its structural origin remain topics of interest. In this work, we use a statistical mechanics approach to predict the composition-structure relationship in mixed modifier Na2O-K2O-SiO2 glasses. This is achieved by accounting for the enthalpy between each pairwise alkali ion and silicate unit interaction. The initial enthalpy parameters are obtained based on experimental structural data for binary Na2O-SiO2 and K2O-SiO2 glasses, which can be transferred to predict the short-range order structure of mixed modifier glasses without additional free parameters. To this end, we have performed 29Si magic angle spinning NMR spectroscopy measurements on y(xNa2O-(1 - x)K2O)-(100 - y)SiO2 glasses with x = 0, 0.25, 0.5, 0.75, and 1 and y = 34, 42, and 50. Good agreement between experimental data and model predictions are observed. Finally, we use this information to discuss the relative entropic and enthalpic contributions to the mixed modifier effect in silicate glass structure.

Structure of lead silicate glasses and its correlation with photoelastic properties

Short-range structures of xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses were studied by neutron diffraction and Reverse Monte Carlo modeling. Si–O atomic pair correlation distributions are symmetrical and show peaks in the range: 1.60–1.64 ± 0.02 A. Si4+ are tetrahedrally co-ordinated with oxygen, whereas the Pb–O and O–O atomic pair correlation distributions are broad and asymmetrical due to the existence of wide range of Pb–O and O–O distances in the glass network. The peak positions in the Pb–O atomic pair correlations shift from 2.60 ± 0.05 to 2.42 ± 0.05 A on increasing PbO concentration from 50 to 65 mol%. Pb2+ exist in PbOx (x = 3, 4, 5 and 6) structural units, and the average Pb–O coordination is constant and is in the range of 4.08 ± 0.11 to 4.14 ± 0.08. The O–Si–O bond angles distributions are broad and asymmetrical with peak values in the range of 91° to 109°, and deviate significantly from the value of 109.5° in the ideal tetrahedral structural units. The short-range structural properties of glasses i.e. the cation-oxygen coordination numbers and bond lengths were used to predict the photoelastic properties of the glasses by the Zwanziger model, and it is concluded that xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses should exhibit the properties of zero-stress birefringence.

Effect of CeO2 on the Structure of Silicate Glass Cured Body

In this paper, samples of xCeO2·(100-x) (SiO2·Al2O3·CaO) (x: 0∼15) glass solidified body was prepared by a high temperature melting method. The structural characteristics and thermal stability of CeO2 silicate glass-cured bodies were characterized by means of density porosity test, XRD, Raman, DSC and SEM. The results show that the addition of CeO2 does not change the basic structure of the glass, which is located in the pores of the silicate glass grid and plays a network modification role. When the added amount is less than 5% wt, homogeneous glass is easily formed. CeO2 is uniformly distributed in the glass body, and no enrichment occurs. When the added amount is more than 8% wt, CeO2 easily crystallizes during cooling.

Isolation, characterization and source analysis of radiocaesium micro-particles in soil sample collected from vicinity of Fukushima Dai-ichi nuclear power plant

Radioactive caesium was released during the accident of Fukushima Dai-ichi nuclear power plant (FDNPP) into the surrounding environment. In the current work, radiocaesium micro-particles (CsMPs) and radiocaesium-rich soil particles were selectively separated from soil particles as well as from each other using autoradiography-based procedure. The applied separation scheme is based on water dilution followed by drying of the soil sample prior to imaging plate autoradiography. The SEM/EDS investigation of the individual CsMPs showed that these particles have a silicate glass structure and vary in shape with a diameter less than 10 μm. For the first time, a two-stage formation mechanism was suggested for a CsMP based on shape and structure heterogeneity of its two parts. Perfect spherical core might be formed in the first stage with a remarkable lower content of Al, and relatively higher concentrations of Si and K than an outer angulated structure, which might be attached to the core sphere during a late stage.The radiocaesium-rich soil particles have bigger size than CsMPs and have a plate-like structure with cleavages inside the grains, which suggest that these particles might be a weathered biotite. The average radioactivity ratio of 134Cs/137Cs (dated March 11, 2011) in the investigated particles was found to be 1.05 ± 0.01, which confirmed that the radiocaesium in CsMPs and in the contaminated soil particles has the same source of origin, which could be unite 3 of FDNPP.

New insights into the structure of sodium silicate glasses by force-enhanced atomic refinement

Atomistic simulations can offer direct access to the atomic structure of glasses, which is otherwise invisible from conventional experiments. However, molecular dynamics (MD) simulations of glasses based on the melt-quenching technique remain plagued by the use of high cooling rates, while reverse Monte Carlo (RMC) modeling can yield non-unique solutions. Here, we adopt the force-enhanced atomic refinement (FEAR) method to overcome these limitations and decipher the atomic structure of a sodium silicate glass. We show that FEAR offers an unprecedented description of the atomic structure of sodium silicate, wherein the simulated configuration simultaneously exhibits enhanced agreement with experimental diffraction data and higher energetic stability as compared to those generated by MD or RMC. This result allows us to reveal new insights into the atomic structure of sodium silicate glasses. Specifically, we show that sodium silicate glasses exhibit a more ordered medium-range order structure than previously suggested by MD simulations. These results pave the way toward an increased ability to accurately describe the atomic structure of glasses.

The influence of redox state on the location of iron ions in the structure of silicate glass with high iron content

With the help of Mössbauer investigations, it was found that tetrahedral coordination is present in the alkali silicate glass system for both Fe2+ and Fe3+ in oxidising molten glass. The reduction process changes the coordination number of iron from 4 to 6. It is clear that the iron content has a much stronger influence on the properties than the redox state. In lower temperatures, the difference between reducing and oxidising conditions can be clearly observed, which at high temperatures lies within the measurement error range. A change in the redox state has a significant influence on the transition temperature, density, microhardness, and on the expansion coefficient. Therefore, it can be concluded that after reduction, the iron ions in the structure play a similar role to that of network transducers.

Structural features of sodium silicate glasses from reactive force field‐based molecular dynamics simulations

AbstractAtomistic computer simulations can provide insights into silicate glass‐environment interactions with the recent development of reactive potentials. However, the accuracy of generated glass structures with these potential was usually not fully examined. In this paper, the capability of the reactive force field (ReaxFF) to describe the short and medium range structure features of sodium silicate glasses in molecular dynamics simulations is investigated by comparing a widely used partial charge pairwise potential and available experimental data. Glass structure information such as pair distribution function (PDF), coordination number, Qn species, neutron broadened structure factor, and X‐ray broadened structure factor of the glass structures from ReaxFF simulations were calculated and compared to evaluate the generated glass structure. Advantages and limitations of the potentials and glass forming procedures, as well as areas of further improvement, were discussed. The results show that the recently refined ReaxFF parameters through the proposed procedure enable the simulations of sodium silicate glass structures with minimal defects, which paves the way to investigate water‐glass interaction mechanisms with the reactive enabled potentials.

Pressure-Induced Structural Transitions in Na–Li Silicate Glasses under Compression

The atomic structures of alkali silicate glasses with more than two types of nonframework cations (e.g., Li and Na) at high pressure provide insights into the effects of pressure on the transport p...

Structural studies of potassium silicate glasses with fixed iron content and their relation to similar alkali silicates

Silicate glasses containing potassium oxide of molar percentages 12%, 16% and 20% each with 8% iron oxide have been prepared and examined by Raman, Extended X-ray absorption fine structure (EXAFS) and Mössbauer spectroscopy. For the 12% and 16% of iron potassium silicate glasses, analysis of the Raman data indicated a maximum of Q2 linkages of the silica tetrahedra while for the 20% iron potassium silicate sample, the Q3 and Q4 linkages were dominant. EXAFS data found the Fe ion to be in tetrahedral coordination with oxygen and a FeO distance of ~1.85 Å. The isomeric shifts in the Mössbauer spectra found the Fe3+ to Fe2+ ratios to vary with potassium content from 2:1 for the 12% to 8:1 for the 20% potassium glass. Spectral areas showed iron ions to be tetrahedrally coordinated to oxygen with quadrupole splitting showing distortion of these units. From the distribution of Qn linkages it is found that at 16 mol% of the alkali, the lithium iron silicates have more open structures than the sodium and potassium iron silicate glasses. The more open structure of sodium silicate glass when iron is added could have important implications for its use as an electrolytic material.

Structures of silicate glasses with varying sodium and fixed iron contents

Silicate glasses have been synthesised with a fixed 8 mol% of Fe3O4 and sodium oxide varying from 12 mol% to 20 mol%. The environment of the Fe ion was examined by Extended X-ray Absorption Fine structure and Mössbauer spectroscopy which have shown tetrahedral coordination of oxygen around Fe regardless of the oxidation state of iron. Mössbauer data indicate increasing; distortion of these tetrahedral units and Fe3+ to Fe2+ ratios, with increasing sodium concentration. Raman spectroscopic studies have shown the presence of Qn linkages for n = 0 to n = 4. For the sodium silicate glass without iron, the single most common linkage is Q3 (~ 50%) suggesting the role of the alkali to be disruptive to the continuity of the silica random network. For the iron containing glasses, the main linkage is Q2 (~ 65%). However, in the latter glasses the fraction of Q3 linkages although considerably less (~10% to ~20%) than Q2 is shown to increase with alkali content due to the concomitant rise of Fe3+ ions which are known to be network formers.

Effects of annealing on density, glass transition temperature and structure of tellurite, silicate and borate glasses

Barium tellurite, lead tellurite, molybdenum tellurite, lead silicate and bismuth borate glasses of the compositions: xBaO-(100-x)TeO2 (x = 10, 15 and 20 mol%), xPbO-(100-x)TeO2 (x = 15 and 20 mol%), 25MoO3-75TeO2, xPbO-(100-x)SiO2 (x = 50, 60 and 65 mol%) and 40Bi2O3-60B2O3 were prepared by melt-quenching. The effects of long duration thermal annealing (below the respective glass transition temperature (Tg) values) on the density, thermal properties and the short-range structure of glasses were studied. Density increases on average by about 0.5% to 1% and Tg values show drastic increase in the range of 8 °C-64 °C after annealing. Raman and FTIR studies were performed on glasses before and after annealing, FTIR studies found that bismuth borate glasses show a small but significant increase in the fraction of tetrahedral borons in the borate network with annealing. Raman studies on lead metasilicate glass showed an increase in the concentration of SiO4 units that contain three bridging oxygens. Raman and FTIR spectra of all annealed barium and lead tellurite glasses were indistinguishable from those of the initial samples, however the FTIR spectra of annealed 25MoO3-75TeO2 glass show changes in the relative intensities of the peaks due to MoO vibrations along with the growth and sharpening of low frequency Raman bands, furthermore this glass also showed large differences in its crystallization and melting properties during thermal analysis.

Development of a ReaxFF Reactive Force Field for NaSiOx/Water Systems and Its Application to Sodium and Proton Self-Diffusion

We present the development of a ReaxFF reactive force field for Na/Si/O/H interactions, which enables reactive molecular dynamics simulation of the sodium silicate–water interfaces. The force field parameters were fitted against various quantum mechanical calculations, including equations of state of different NaSiOx crystalline phases, energy barriers of a sodium cation’s transport within the sodium silicate crystal structure, interactions between the hydroxylated silica surface and sodium cation–water systems, and dissociation energies of [NaOH–n(H2O)] (n = 1–6) clusters. After the optimization process, we validated the force field capability through calculating the structures of sodium silicate crystals and glasses and transport properties of sodium ions and protons within the amorphous structures. The force field was also applied to validate the dissociation behavior of sodium hydroxides within the bulk water. Our results with the developed force field are relevant to detailed chemical dissolution mec...

Probing the structure of Fe-free model basaltic glasses: A view from a solid-state 27Al and 17O NMR study of Na-Mg silicate glasses, Na2O-MgO-Al2O3-SiO2 glasses, and synthetic Fe-free KLB-1 basaltic glasses

The extent of structural disorder in multi-component basaltic (mafic) melts with varying compositions (particularly, Mg content) and the formation depth has not been well understood. Here, we explore the structure of Mg-rich silicate glasses including Na-Mg silicate glasses, NaO-MgO-Al2O3-SiO2 (NMAS) glasses in a nepheline (NaAlSiO4)-forsterite (Mg2SiO4)-quartz (SiO2) eutectic composition, and synthetic equivalents of basaltic glasses generated by partial melting of upper mantle peridotite (KLB-1) in a multi-component CaO-MgO-Na2O-K2O-Al2O3-TiO2-SiO2 system using high-resolution solid-state nuclear magnetic resonance (NMR). The 2-dimensional (2D) 17O 3Q (triple quantum) magic angle spinning (MAS) NMR spectra for those multi-component glasses revealed the nature of diverse aspects of structural disorder. Non-bridging oxygens (NBOs) apparently prefer proximity toward Ca2+ and Mg2+, whereas bridging oxygens (BOs) prefer to be near Na+, confirming a stronger interaction between NBOs and high field-strength cations in multi-component basaltic melts. The changes of oxygen configurations with increasing Mg contents provide implications for the structural evolution of basaltic melts with varying formation depth. Thus, while the pressure effect remains to be explored, considering the changes in melt composition alone, the NBO fraction of the KLB-1 basaltic melts increases with increasing melting depth of KLB-1 peridotite.The 27Al 3QMAS NMR spectra for multi-component KLB-1 basaltic glasses reveal non-negligible fraction of [5]Al that increases with increasing Mg content. The fraction of [5]Al in natural basaltic magma is expected to increase with melting depth of KLB-1 peridotite. The 27Al NMR quadrupolar coupling constant for [4]Al in multi-component silicate glasses systematically increases with Mg content, indicating an increase of the topological distortion (variation of bond angle and length distribution and network distortion) around [4]Al in the basaltic glasses. The observed increase in the extent of structural disorder in basaltic melts with Mg content may increase the overall configurational and topological entropy. While further confirmation is necessary, the changes in melt polymerization observed from 17O NMR spectra and network disorder around Al imply the decrease in melt viscosity in the complex silicate melts with varying formation depth of KLB-1 basaltic melts.

Effect of doping La2O3 on the structure and properties of the titanium barium silicate glass

Glasses with the composition 50SiO2-20TiO2-15BaO-7.5SrO-7.5CaO doped varied content of La2O3 have been prepared by the conventional melt quench technique. The effect of La2O3 on structure of the glasses was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectra and Raman spectra. The density, thermal stability and dielectric properties of glass were measured and compared by the Archimedes method, differential thermal scanning analysis (DSC) and impedance spectroscopy, respectively. The results showed that the coordination of the titanium remained invariable with the addition of La2O3, while the number of Si-O-Ti bonds increased and the distribution of Qn changed. And the depolymerization of the glass network was observed. The thermal stability and resistance to crystallization increased significantly for glass containing 4 mol% of La2O3 resulting from the strong strength of LaO bond and the La3+ clustering. However, the resistance to crystallization for glasses was decreased with further increasing La2O3. The dielectric constant of glass decreased first and then increased with the increase of La2O3 content, while the dielectric loss was almost constant.

Quantitative prediction of the structure and properties of Li2O–Ta2O5–SiO2 glasses via phase diagram approach

AbstractTantalum silicate glasses serve as laser host materials to take advantage of their high refractive index and the ability to tailor their physical properties in the design of high‐performance photonic and photoelectric components. However, successful attainment of feature control in tantalum‐doped materials remains a longstanding problem due to the limited understanding of local structure around the tantalum ions, a problem that lies at the heart of predicting the micro‐ and macroscopic properties of these glasses. Herein, we present a novel approach for predicting the local structural environments in tantalum silicate glass based on a phase diagram approach. The phase relations and glass formation region of Li2O–Ta2O5–SiO2 ternary systems are explored to calculate the structure and additive physical properties of lithium tantalum silicate glasses. These measured and calculated results are in good quantitative agreement, indicating that the phase diagram approach can be applied broadly to Li2O–Ta2O5–SiO2 ternary glass systems. Using the phase diagram approach, the local structure of tantalum can be directly obtained. Each Ta atom is surrounded by six atoms, and its polyhedron, the TaO6 octahedron, bonds through oxygen to Li and Ta. As a network modifier, Ta5+ depolymerizes the silicate glass structure by modulating the local structure of lithium atoms in Li2O–Ta2O5–SiO2 ternary glass system. The compositional dependence of structure in lithium tantalum silicate glasses is quantitatively determined based on the structure of the nearest neighbor congruent compound through the lever rule. These findings offer a precise prediction of tantalum silicate glass properties with quantitative control over local structural environment of the disordered materials.

Observation of efficient Er3+:4I11/2→4I13/2 transition in highly Er3+ doped germanosilicate glass

Highly rare earth（RE）ions doped glass laser materials can produce efficient single frequency mid-infrared laser. In this work, a series germanosilicate glasses with various high erbium-doping concentration (up to 4 mol%) and without concentration quenching are fabricated. Spectroscopic properties and energy transfer (ET) mechanism of efficient Er3+:4I11/2 →4I13/2 transition have been investigated in detail upon a conventional 980 nm Laser Diode. The dense structure of silicate glass can be dissolved effectively by the introduction of GeO2, which was analyzed by Raman spectra, so that the compatibility and luminous intensity of RE ions were improved. The high predicted spontaneous transition probability (Arad = 37.65 s−1) based on the Judd-Ofelt theory and large calculated emission cross section (8.8 × 10−21 cm2) are obtained. The above results indicate that these glasses are promising to be the single frequency mid-infrared laser material.

Compositional dependence of structure and wetting properties of CoO-doped silicate glass for porcelain enamel

Compositional dependence of structure and wetting properties of CoO-doped silicate glass for porcelain enamel