The effect of fluoride on the Fe2+/Fe3+-redox equilibrium in glass melts in the system Na2O/NaF/CaO/Al2O3/SiO2

Liquids with the base compositions (16 − x/2)Na₂O · xNaF · 10CaO · 74SiO₂ (x = 0, 1, 3, and 4) and (10 − x/2) · Na₂O · xNaF · 10CaO · yAl₂O₃ · (80 − y)SiO₂ (x = 0, 1, 3, 5 and y = 5 and 15) doped with 0.25 mol% Fe₂O₃ were studied by means of square-wave voltammetry in the temperature range from 1000 to 1500 °C. With increasing temperature, the redox equilibria were shifted to the reduced state. Also while increasing the alumina concentration, the Fe²⁺/Fe³⁺-redox equilibrium is shifted to the reduced state. In the soda-lime–silica melt the addition of fluoride shifts the equilibrium to the oxidized state, while in the aluminosilicate melts with 15 mol% Al₂O₃, the equilibrium is shifted to the reduced state. In the aluminosilicate melts with 5 mol% Al₂O₃, the equilibrium was not affected by the fluoride concentration. This is explained by the structure of the respective glass compositions.     

Electrical conductivity of silicate glasses with tetravalent cations substituting Si

The effects of substituting Si by M^4 + cations in soda-lime silica glasses were analyzed by impedance spectroscopy in the frequency range of 1 Hz–1 MHz. The glass composition was (mol%) 22Na₂O·8CaO·65SiO₂·5MO₂, M = Si, Ti, Ge, Zr, Sn, and Ce. Although the Na⁺ concentration in the glasses is constant, the Zr-containing glass exhibits the highest dc conductivity and the lowest activation energy, while the Ce-containing glass exhibits the lowest conductivity. The activation energies obtained experimentally agree with those obtained by a theoretical equation proposed by Anderson and Stuart. The differences in electrical conductivity presented by the several M-containing glasses are attributed to the effect that the M^4 + ion has on the mobility of the diffusing Na⁺ ion.     

Square-wave voltammetry and impedance spectroscopy in tin doped melts with the compositions xNa2O · 15Al2O3 · (85 − x)SiO2 (x = 8.5, 11 and 16)

Glasses with the base compositions xNa₂O · 15Al₂O₃ · (85 ? x)SiO₂ (x = 8.5, 11 and 16) doped with 0.5 mol% SnO₂ were investigated by both square-wave voltammetry and impedance spectroscopy in the temperature range from 1300 to 1600 °C. Each recorded square-wave voltammogram exhibits a well pronounced peak attributed to the Sn²⁺/Sn⁴⁺-redox pair. Impedance spectra were measured in a frequency range from 0.1 to 10⁵ s^?1 as a function of the superimposed dc-potential and were simulated using an equivalent circuit taking into account the resistivity of the melt, the electrochemical double layer, a resistor attributed to a kinetically hindered electron transfer and a Warburg parameter which accounts for the diffusion process of Sn⁴⁺ and Sn²⁺ to and from the electrode. Additionally, two impedance elements, a resistor and a capacitance both attributed to adsorption processes were necessary to fit the impedance spectra.     

Square-wave voltammetry and impedance spectroscopy in iron-doped melts of the system Li2O/Al2O3/SiO2

Glass melts with the basic compositions xLi₂O · 15Al₂O₃ · (85 − x)SiO₂ (x = 8.5, 11, 13.5, 16 and 18.5) doped with 0.25 mol% Fe₂O₃ were studied by square-wave voltammetry and impedance spectroscopy at temperatures in the range from 1100 to 1600 °C. The square-wave voltammograms show a pronounced peak attributed to the reduction of Fe³⁺ to Fe²⁺. The attributed peak potentials which are equal to the standard potentials of the redox pair decrease linearly with the temperature. Impedance spectra measured could be simulated using an equivalent circuit attributed to a simple electron transfer reaction controlled by diffusion.     

Thermal conductivity of mixed alkali silicate glasses at low temperature

Thermal conductivity of glass is one of the fundamental properties of it. However, that has not been studied enough. That of only less than 20 compositions has been measured below the room temperature. In this study, we measured the thermal conductivity of xNa₂O · (100 ? x)SiO₂ and (33 ? y)Na₂O · yCs₂O · 67SiO₂ glasses by a transient heating method in the temperature range from about 150 K to room temperature. The conductivity of xNa₂O · (100 ? x)SiO₂ is found to decrease with the increase in alkali content. The dominant factor of this behavior is the decrease in phonon mean free path, which is due to the increase of non-bridge oxygen. Thermal conductivity of (33 ? y)Cs₂O · yNa₂O · 67SiO₂ is decreased with the increase in Cs₂O/(Na₂O + Cs₂O) ratio. The dominant factor of this behavior is the decrease of sound velocity. However, composition dependence of the phonon mean free path also affects the thermal conductivity. Phonon mean free path of 33Cs₂O · 67SiO₂ glass is longer than that of 33Na₂O · 67SiO₂ glass, and should be related to the change in distribution of structural unit in glass. In addition, phonon mean free path of mixed alkali glasses are shorter than that of single alkali glasses.     

Redox reactions during temperature change in soda-lime–silicate melts doped with copper and iron or copper and manganese

Glasses with the base composition 16Na₂O · 10CaO · 74SiO₂ doped with copper and iron or copper and manganese were studied by high temperature UV–vis–NIR spectroscopy. The spectra exhibited distinct absorption bands attributed to the respective transition metal ions present (Cu²⁺, Fe²⁺, Fe³⁺, Mn³⁺). In glasses doped with only one polyvalent element, the absorption decreases linearly with increasing temperature, the absorption bands are shifted to smaller wave numbers and get broader. In glasses doped with two types of transition metals, the situation is the same up to a temperature of around 550 °C. At larger temperature, the Cu²⁺-absorption in glasses also co-doped with iron increases again, while in glasses doped with both copper and manganese the absorption is approximately the same as in glasses solely doped with copper. It is shown that this is due to redox reactions between polyvalent species. These reactions are frozen in at temperatures <550 °C.     

Continuous compositional changes of crystal and liquid during crystallization of a sodium calcium silicate glass

This paper deals with a systematic study of crystal nucleation and growth kinetics in a 14.6Na₂O–34.0CaO–51.4SiO₂ mol% glass, which is close to the CaO · SiO₂–Na₂O · SiO₂ pseudo-binary section, just left of the stoichiometric Na₂O · 2CaO · 3SiO₂ (N₁C₂S₃) compound. We show that crystallization begins with nucleation of a Na_4+2xCa_4−x[Si₆O₁₈] (0 < x < 1) solid solution that is enriched in sodium as compared with both parent glass and the N₁C₂S₃ compound; while a fully crystallized sample is composed only by a solid solution that is stable at very high temperatures, but is metastable in the temperatures under investigation. We thus confirm a continuous compositional change of the crystals during the course of crystallization.     

EPR and magnetic susceptibility studies of B2O3–Bi2O3–Gd2O3 glasses

Glasses of the xGd₂O₃ · (100 − x)[B₂O₃ · Bi₂O₃] system with 0.5 ⩽ x ⩽ 10 mol% were studied by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Data obtained show that for low gadolinium oxide contents of the samples (x ⩽ 3 mol%) the Gd³⁺ ions are randomly distributed in the host glass matrix and are present as isolated and dipole–dipole coupled species. For higher gadolinium oxide contents of the samples (x > 3 mol%) the Gd³⁺ ions appear as both isolated and antiferromagnetically coupled species. The EPR spectra of the glasses reveal resonance sites with an unexpected high crystalline field in addition to the ‘U’ spectrum, typical for Gd³⁺ ions in disordered systems. This absorption line is due to Gd³⁺ ions that replace Bi³⁺ ions from the host glass matrix and could play the network unconventional former role in the studied glasses.     

Structure of amorphous NaCl–glucose system studied by X-ray diffraction and IR methods

X-ray diffraction and diffuse reflection IR spectroscopic measurements have been carried out on amorphous NaCl–glucose mixtures, a-(NaCl)_x(glucose)_1−x, with x = 0, 0.05, 0.1 and 0.15, in order to obtain structural information on the intermolecular hydrogen-bonded interaction between glucose molecules affected by the presence of NaCl. The difference distribution function Δg^inter(r) was derived from the Fourier transform of the difference intermolecular interference term Δi^inter(Q) between X-ray intermolecular interference terms observed from amorphous NaCl-glucose and pure glucose samples. A negative peak appears at r ≈ 2.5 Å in the Δg^inter(r) observed for the 10 mol% NaCl sample, while, the Δg^inter(r) for the 15 mol% NaCl sample does not show pronounced negative peak. On the other hand, the IR spectra for the O–H stretching region (2300 ⩽ ν ⩽ 3800 cm⁻¹) indicate that hydrogen bonds between glucose molecules are significantly collapsed in the samples containing 5–15 mol% NaCl. These results imply that the contribution from the Na⁺⋯Cl⁻ contact ion pair is dominated in the 15 mol% NaCl sample.     

Neutron diffraction study of sodium borosilicate waste glasses containing uranium

The effect of uranium oxide on the structure of sodium borosilicate host glasses has been studied by neutron diffraction. The samples were prepared by quenching the melted mixtures of composition 70 wt% [(65 − x)SiO₂ · xB₂O₃ · 25Na₂O · 5BaO · 5ZrO₂] + 30 wt% UO₃ with x = 5, 10 and 15 mol%. It was found, that the U-loaded glasses posses good glass and hydrolytic stability. An enhanced probability for inter-mediate atomic correlations at around 4.8 Å has been established. The RMC simulation of the neutron diffraction data is consistent with a model where the uranium ions are incorporated into interstitial voids in the essentially unmodified network structure of the starting host glass. The U–O atomic pair correlation functions show a sharp peak at around 1.7 Å, and several farther distinct peaks are at 2.8, 3.6 and 4.1 Å. The uranium ions are coordinated by six oxygen atoms in the 1.6–3.4 Å interval.     

Thermal and spectroscopic properties of Tm3 + doped TZPPN transparent glass laser material

In this work a transparent bulk glass with the mol% composition 76TeO₂·10ZnO·9.0PbO·1.0PbF₂·3.0Na₂O doped with Tm^3 + has been synthesized. Results of differential thermal analysis (DTA) indicate a high thermal stability and low tendency to crystallization of this glass. The refractive indices at different wavelengths, the Urbach energy, the optical energy gap, the Sellmeier gap energy and the dispersion energy have been estimated. Spectroscopic quality factor of Tm^3 + was evaluated from optical absorption spectra. Electric and magnetic dipole transition probabilities, branching ratios, and radiative lifetimes of several excited states of Tm^3 + have been predicted using calculated intensity Judd–Ofelt parameters. The classical McCumber theory has been applied to evaluate the emission cross-sections for ³F₄ → ³H₆ transition around 1.8 μm. This study shows that TZPPN glass doped with Tm^3 + ions is a promising candidate for laser applications.     

Mixed transition-ion effect in the glass system: Fe2O3-MnO-TeO2

In earlier studies on phosphate and tellurite glasses containing vanadium and iron oxides, non-linear variation of physical properties as functions of the ratios of the transition ions (V/V + Fe) were observed. The most striking effect was observed with electrical conductivity, where a 3 orders of magnitude reduction in conductivity was observed at a V/V + Fe ratio of ~ 0.4. The effect was termed Mixed Transition-ion Effect or MTE. In phosphate glasses, however, MTE was not observed when one of the transition ions was manganese. It was concluded that Mn does not contribute to conduction in these glasses. In the present study, we demonstrate a mixed transition ion effect in tellurite glasses containing MnO and Fe₂O₃ (xFe₂O₃(0.2 ? x) MnO0.8TeO₂ with x varying from 0 to 0.2). A maximum in the property at an intermediate composition (x = 8.5 mol%), was observed in DC resistivity, activation energy, molar volume etc. Mossbauer and optical absorption (UV–VIS–NIR) measurements were performed on these glasses and the transport mechanism has been identified to be hopping of small polarons between Fe^3 + (Mn^3 +) and Fe^2 + (Mn^2 +) sites.     

Network structure of multi-component sodium borosilicate glasses by neutron diffraction

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 − x)SiO_2. · xB₂O₃ · 25Na₂O · 5BaO · 5ZrO₂, x = 5–15 mol%. The maximum momentum transfer of the experimental structure factor was 30 Å⁻¹, which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si–O and Si–Si distributions are similar for all glassy samples, suggesting that the Si–O network consisting of tetrahedral SiO₄ units is highly stable even in the multi-component glasses. The B–O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 Å and 1.60 Å, the latter equals the Si–O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O–O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO₃ units, and the silicon rich network is formed by a mixed continuous network of ^[4]Si–O–Si^[4] with several different ^[4]B–O–Si^[4] and ^[3]B–O–Si^[4] linkages.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Structural modifications induced by addition of copper oxide to lead–phosphate glasses

xCuO(1-x)[P₂O₅·PbO] glass system with 0 ≤ x ≤ 50 mol% was prepared and investigated by means of EPR and IR spectroscopy in order to evidence the structural changes induced by different amounts of copper ions. EPR spectra analysis together with EPR parameters has indicated a distorted tetragonal symmetry – named tetrahedral local symmetry – for Cu^2 + ions in the studied glasses. A change in the shape of EPR spectra was also observed as for small CuO concentration (x < 20 mol%) these glasses present an asymmetrical line typical for isolated ions and for high CuO content this line is replaced by a symmetrical one characteristic of clustered ions through dipole–dipole interactions. IR spectra of the studied glasses put in evidence a strong depolymerization effect with a gradual increase of CuO. The shift of PO asymmetric stretching vibration band to lower wave number can be explained by the increase of PO₄ tetrahedra charge density leading a more ionic and less covalent bonding.     

Optical phonons and Raman scattering in ternary II–VI spheroidal nanocrystals embedded in a glass matrix

Theoretical and experimental studies of the spatial phonon confinement in ternary CdS_xSe_1−x nanocrystals embedded in a glass matrix formed by the composites (40)SiO₂₋(30)Na₂CO₃–(29)B₂O₃–(1)Al₂O₃ (mol%) + [(2)CdO + (2)S + (2)Se] (wt%) were carried out. From the analysis of the surface phonon modes, the theoretical procedure has allowed the determination of the geometrical characteristics of the nanocrystals. The calculated frequencies were compared with the experimental values obtained from the Raman spectra of CdS_xSe_1−x nanocrystals grown under different thermal treatments. A good correlation between the experimental and calculated CdS-like and CdSe-like surface optical modes was observed. The Raman selection rules and their connection with the nature of the surface optical phonons is discussed in order to use Raman spectroscopy as a probe to determine the composition x and the geometrical shape of the semiconductor nanocrystals.     

Sodium tracer diffusion in sodium boroaluminosilicate glasses

Sodium tracer diffusion coefficients, D*_Na, have been measured using the radioactive isotope Na-22 in sodium boroaluminosilicate (NBAS) glasses containing either a small amount of As₂O₃ or Fe₂O₃. The chemical compositions of the first type of glasses are given by the formula [(Na₂O)_0.71(Fe₂O₃)_0.05(B₂O₃)_0.24]_0.2[(SiO₂)_x(Al₂O₃)_1 ? x]_0.8 and those of the second type of glasses correspond to the formula [(Na₂O)_0.73(B₂O₃)_0.24(As₂O₃)_0.03]_0.18[(SiO₂)_x(Al₂O₃)_1 ? x]_0.82. Tracer diffusion measurements were performed at different temperatures between 198 and 350 °C. Pre-annealing of the glass samples at their glass transition temperatures in common air was found to lead to changes in the values of sodium tracer diffusion coefficients. For the NBAS glasses containing Fe₂O₃, after pre-annealing for 5 h, the activation enthalpy derived for the sodium tracer diffusion increases almost linearly from 57.5 to 71.3 kJ/mol with a decrease in the alumina content while the pre-exponential factor of the sodium tracer diffusion coefficient increases from 2.1 · 10^? 4 to 5.3 · 10^? 4 cm²/s. For the iron-free NBAS glasses pre-annealed for 5 h, the activation enthalpy varies between 63.9 and 71.4 kJ/mol while the pre-exponential factor varies between 1.5 · 10^? 4 and 1.2 · 10^? 3 cm²/s. In addition, it was observed that the considered glasses take up water when annealed at 300 °C in wet air with P_H2O = 474 mbar.     

Formation and thermal stability of Pd-based bulk metallic glasses

The glass-forming ability and thermal stability of bulk glassy Pd₇₉Cu₆Si₁₀P₅ alloy were studied by substitution of Cu with Ag and with Au + Ag from 0 to 6 at.%. The results indicated that the small addition of Ag strongly affects the thermal stability and glass-forming ability of the Pd₇₉Cu₆Si₁₀P₅ alloy. The alloy doped with 4 at.% Ag (Pd₇₉Cu₂Ag₄Si₁₀P₅) exhibits the largest glass-forming ability among the Pd₇₉Cu_6−xAg_xSi₁₀P₅ (x = 0–6 at.%) alloys. The critical diameter for glass formation of this alloy reaches as large as 7 mm by copper mold casting. On the other hand, the multi-addition of Au + Ag does not increase the glass forming ability though the Ag and Au are similar in atomic size. The largest glass forming ability is obtained at 1 at.% Au + 2 at.% Ag among the Pd₇₉Cu_6−x−yAu_xAg_ySi₁₀P₅ (x = 1–4 at.%, y = 1–3 at.%) alloys. The critical diameter of this alloy is 5 mm by copper mold casting.     

Influence of valence and coordination of manganese ions on spectral and dielectric features of Na2SO4–B2O3–P2O5 glasses

Sodiumsulpho borophosphate glasses with composition (40 ? x)Na₂SO₄–30B₂O₃–30P₂O₅: xMnO with x ranging from 0 to 5.0 mol% were manufactures. Dielectric spectra have been studied over a wide frequency range of 10²–10⁵ Hz and in the temperature range within 30–250 °C. The valance states of manganese ions and their ligand coordination in the glass network have been investigated using optical absorption, luminescence and ESR spectroscopy. The analysis of the these results has indicated that the manganese ions exist both in Mn²⁺ as well as in Mn³⁺ states and occupy prevailingly octahedral positions and serve as modifiers similarly to Na⁺ ions The values of dielectric parameters (dielectric constant, ε′(ω), loss tan δ and ac conductivity, σ_ac) were found to increase with increasing MnO content. They play a role of modifiers similarly to Na⁺ ions, create bonding defects and free ions viz., [SO₄]^2?, [POO_1/2O₂]^2?, [POO_0/2O₃]^3–, Na⁺ and (NaSO₄)^?. The migration of these charge carriers would build up space charge polarization and may be responsible for the enhanced dielectric parameters. The ac conductivity also is enhanced with increasing MnO content. The mechanism responsible for such increase is well explained based on the modifying action of Mn²⁺ ions.     

Electrooptical Kerr phenomenon and Raman spectroscopy of one lithium–niobium–silicate glass-forming system

Raman spectra and electrooptical Kerr coefficients of glasses belonging to one lithium–niobate–silicate glass-forming system xNb₂O₅ · (66 ? x)SiO₂ · 19Li₂O · 11K₂O · 2B₂O₃ · 2CdO are studied. It has been found that these glasses demonstrate a record value of electrooptical Kerr coefficient; the glass with x = 35 showed electrooptical Kerr coefficient equal to 266 × 10^?16 m/V². Using Raman spectroscopy combined with the concept of Constant Stoichiometric Groupings, a correlation of electrooptical Kerr coefficients of these glasses with the content of Li₂O · Nb₂O₅ (or 2LiNbO₃) groupings has been demonstrated. The hypothesis that electrooptical Kerr sensitivity of glasses is related to the ordered regions with composition and symmetry corresponding to some of known electrooptical crystals has been verified. These regions, which the authors called ‘Crystal Motifs’, are identified with the groupings found in studying Raman spectra of the glasses.