Cation Field Strength Research Articles

Sintering, Crystallization, and Dielectric Behavior of Barium Zinc Borosilicate Glasses—Effect of Barium Oxide Substitution for Zinc Oxide

Barium zinc borosilicate glasses with a molar composition xBaO‐(60−x)ZnO‐30B2O3‐10SiO2, where x ranged from 0 to 60 mol%, were prepared using melt‐quenching method. The effect of BaO substitution for ZnO on the sintering, crystallization, and dielectric characteristics has been investigated. The behavior of the studied barium zinc borosilicate glasses was mainly determined by the relative amount of the structural modifier oxides (BaO and ZnO) and the ionic size, and field strength of the modifying cations (Ba2+, Zn2+). Increased amounts of BaO decreased both glass transition temperature and crystallization temperature, while increasing the relative dielectric constant. Sintering occurred before crystallization for glasses where substitution of BaO for ZnO was up to 30 mol%, but for higher substitution levels, crystallization occurred during the sintering process hindering densification.

Properties and Structures of RE2O3–Al2O3–SiO2 (RE = Y, Lu) Glasses Probed by Molecular Dynamics Simulations and Solid-State NMR: The Roles of Aluminum and Rare-Earth Ions for Dictating the Microhardness

By combining molecular dynamics (MD) simulations with 29Si and 27Al magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we present a comprehensive structural report on rare-earth (RE) aluminosilicate (AS) glasses of the RE2O3–Al2O3–SiO2 (RE = Y, Lu) systems, where the latter is studied for the first time. The structural variations stemming from changes in the glass composition within each RE system—as well as the effects of the increased cation field-strength (CFS) of Lu3+ relative to Y3+—are explored and correlated to measured physical properties, such as density, molar volume, glass transition temperature, and Vickers hardness (HV). 29Si NMR reveals a pronounced network ordering for an increase in either the RE or Al content of the glass. Al mainly assumes tetrahedral coordination, but significant AlO5 and AlO6 populations are present in all structures, with elevated amounts in the Lu-bearing glasses compared to their Y analogues. The MD-derived oxygen speciation comprises up to 3% of fr...

Composition‐Property‐Structure Correlations of Scandium Aluminosilicate Glasses Revealed by Multinuclear 45Sc, 27Al, and 29Si Solid‐State NMR

Many features of aluminosilicate glasses incorporating a rare‐earth (RE) ion are dictated by its mass and cation field strength (CFS). Sc–Al–Si–O glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass‐transition temperature (Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2O3–Al2O3–SiO2 system. The glasses exhibit uniform and unexpectedly low Tg‐values (≈875°C), but a high microhardness (≈9.3 GPa) that correlates with the Sc2O3 content. 29Si magic‐angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy shows enhanced deshielding and a minor glass‐network ordering as either the Al or Sc content of the glass increases. 27Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%–35%) and AlO6 (≈5%) polyhedra are present in all Sc–Al–Si–O glass structures. 45Sc isotropic chemical shifts (≈92 ppm) derived from MAS and 3QMAS (triple‐quantum MAS) NMR experiments are consistent with ScO6 environments.

Effect of rare-earth elements on the plasma etching behavior of the RE–Si–Al–O glasses

The effect of rare-earth elements on the plasma etching behavior of oxide glasses were investigated to develop the window glass for a plasma processing chamber in the semiconductor industry. Aluminosilicate glasses with various rare-earth elements (Y, Gd and La) were prepared and their optical transmittance and plasma etching depth were evaluated. The plasma etching behavior of the glasses was estimated by X-ray photoelectron spectroscopy analysis at the fluorine plasma exposure surface of the glasses. The rare-earth element in the glass was highly related to various properties such as density, molar volume, mechanical properties and plasma etching depth. The cationic field strength of the rare-earth element more strongly affected the plasma etching depth of the glasses than the sublimation point of the fluorine compounds and this may be related to the plasma etching condition.

INVESTIGATION ON THE EFFECT OF RARE EARTH (RE) CATION TO THE (RE+Ca)SiAlON GLASSES

The main purpose of this study was to determine the change in density, glass transition temperature (Tg) and hardness as a result of compositional modifications in the (RE+Ca)SiAlON oxynitride glasses (RE= Er, Nd, Sm, Eu, Dy, Yb) with a cation ratio in eq% of (1+27):56:16 = (RE+Ca):Si:Al. The amount of nitrogen was kept constant (N=5 eq %). Additionally other series of the (Er+Y):Si:Al:O:N glasses with cation composition 3+25):56:16 were prepared with different amount of nitrogen (where N= 0, 5, 10 eq %) to observe the effect of nitrogen to glass transition temperature. X-Ray diffraction patterns proved that all produced glasses were amorphous. Tg and hardness results of (RE+Ca)SiAlON glasses were revealed that there is a linear relationship between cation field strength (CFS). Density results versus molecular weight and CFS were presented. Additionally, glass transition temperatures of the (Er+Y)SiAlON glasses were further increased with the increasing nitrogen content in the structure. These results are also compared with (RE+Ca)SiAlON glass series.

Network coordination in low germanium alkaline-earth gallate systems: influence on glass formation

Glass formation in a newly formulated low germanium alkaline earth gallate (LGMGa, M = Ca/Mg/Zn/Sr/Ba) system by a high temperature melt quenching route is reported here. The proportionate ratios of tetrahedral to octahedral coordination of both Ga3+ and Ge4+ network cations are found to be crucial for vitrification. The enhancement in octahedral coordination led to surface crystallization and phase separation in cast melts. This behavior has been attributed to the overall reduction in tetrahedrally coordinated network units due to the failure of Ca2+ ions in charge compensation of the [GaO4]− tetrahedron. Among different network modifying oxides, BaO in combination with CaO (mixed alkaline earth) containing compositions have proved to yield clear glass formation with improved tetrahedral networking. This has been explained though the basicity equalization concept and also due to efficient charge compensation of the [GaO4]− tetrahedron requiring lower field strength cations like Ba2+. The effective phonon energy of this low germanium calcium barium gallate (LGCBGa) glass is found to be around 650 cm−1, with an extended infrared transparency up to around 7 μm, which is superior to most of the low phonon energy oxide glass systems, making it promising for photonic and mid-infrared luminescence applications. Furthermore, the observed dark yellow to brown coloration in the glass has been attributed to the precipitation of metallic nanoparticles, and this mechanism has been discussed in detail.

EPR spectroscopic studies in (30 − x) Li2O–xK2O–10CdO–59B2O3–1MnO2 multi-component glass system

EPR studies were carried out in (30–x) Li2O–xK2O–10CdO–59B2O3–1MnO2 multi-component glass system to understand the effect of the variation in the alkali ratios on the EPR parameters. The observed EPR spectra of Mn2+ ion exhibits resonances at g=2.0, 3.3 and 4.3. The resonance at g=2.0 is due to Mn2+ ions in an environment close to the octahedral symmetry, where as the resonances at g=3.3 & 4.3 are due to the rhombic surroundings of Mn2+ ions. Hyperfine splitting constant values at g=2.0 and number of paramagnetic centers & paramagnetic susceptibility at different observed resonances were evaluated. These parameters show non linear variation with progressive substitution of Li+ ion with K+ ions may be due to the changes in cation field strengths and local structural variation due to the variation in mixed alkali ion ratios.

Synthesis and Characterization of Lithium Borate Glasses Containing La2O3

The glass series with general formula 15 Li2O–(85 − x) B2O3–x La2O3 was prepared. Electrical and optical properties of these glasses were studied. It is observed that the conductivity of these glasses decreases while density, glass transition temperature and refractive index increases with the addition of La2O3. Ion concentration of La3+ in glasses, polaron radius, field strength, molar refractivity and molar electronic polarizability were calculated. The absorption coefficient and direct optical band gaps are evaluated using the absorption edge calculations. The different factors that play a role for controlling the refractive indices such as electronic polarizability, field strength of cations and rigidity of glass structure are discussed in accordance with the obtained index data.

An Overview of the Structure and Properties of Silicon‐Based Oxynitride Glasses

The silicon oxynitride glasses take advantage of nitrogen bonding to attain high elastic modulus, increased softening temperatures and viscosities, greater slow crack growth resistance, and modest gains in fracture resistance. Of the oxynitride glasses, the Si–Y–Al‐based oxynitride glasses have been most extensively studied and a degree of success has been achieved in understanding how changes in glass composition affect structural parameters and their relationship with properties. More recent studies have focused on the Si–RE–Me oxynitride glasses, where Me is primarily Al or Mg and rare earth (RE) includes most of the lanthanide series elements. These glasses possess a range of elastic, thermal, mechanical, and optical properties, which can be correlated with the strength of the RE bond in terms of the cationic field strength. However, such correlations require knowledge of not only the RE valence state but also its coordination with the anions. Herein, the current state‐of‐the‐art understanding of the properties and structural parameters of oxynitride glasses and their interrelationships are reviewed.

Inhomogeneous distribution of Na+ in alkali silicate glasses

We investigated the Na+ environment in sodium silicate glasses and mixed alkali silicate glasses using 23Na multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy, ab initio molecular orbital (MO) calculations, and Na+ elution analysis. The 23Na MQMAS NMR spectra of Na2O–xSiO2 and (1 − y)Na2O–yM2O–2SiO2 (M = Li, K) glasses showed an inhomogeneous distribution of local structures around Na+, even though spectral deconvolution was impossible. The quantum chemical calculations indicated that the alkali silicate glasses contained both aggregated and isolated Na+ sites. The elution behavior also supported the local structure distribution described above. These results indicated that a cation with a high cation field strength tends to aggregate in mixed silicate glasses.

Effect of rare earths on viscosity and thermal expansion of soda-lime-silicate glass

Viscosity of soda-lime-silicate glass doped with rare earth oxides (Pr 6O 11, Eu 2O 3, Yb 2O 3) was investigated by the rotating crucible viscometer, the melting temperature and activation energy for viscous flow of the studied melt were derived on the basis of the Arrhenius Equation, the coefficient of thermal expansion, glass transition temperature and dilatometric softening temperature were also determined with dilatometry, in order to reveal the effects of rare earth elements on the behavior of soda-lime-silicate glass. The results showed that introduction of rare earth oxides decreased the viscosity of soda-lime-silicate glass and melting temperature of corresponding melt, increased coefficient of thermal expansion of soda-lime-silicate glass. The glass transition temperature, dilatometric softening temperature, and melting temperature of soda-lime-silicate glass doped with rare earth oxides increased with increasing cationic field strength of corresponding rare earth ions.

Viscosity and thermal expansion of rare earth containing soda–lime–silicate glass

Viscosity, coefficient of thermal expansion, glass transition temperature and dilatometric softening temperature of soda–lime–silicate glass doped with rare earth oxides (La 2O 3, CeO 2, Nd 2O 3) were investigated by the rotating crucible viscometer and dilatometry, the melting temperature and activation energy for viscous flow of the studied melt were derived on the basis of Arrhenius equation, in order to reveal the effects of rare earth elements on the behavior of soda–lime–silicate glass. The results show that introduction of rare earth oxides increases the coefficient of thermal expansion, decreases viscosity of soda–lime–silicate glass, and Nd 2O 3 is an exception in viscosity. The glass transition temperature, dilatometric softening temperature, melting temperature and activation energy for viscous flow of soda–lime–silicate glass doped with rare earth oxides increase with increasing cationic field strength of corresponding rare earth ions.

Thermal and physical properties of 30SrO–40SiO 2–20B 2O 3–10A 2O 3 (A = La, Y, Al) glasses and their chemical reaction with bismuth vanadate for SOFC

SiO 2–B 2O 3–SrO–A 2O 3 (A = Y, La, Al) based glasses were investigated for their physical and thermal properties by density measurements and differential thermal analysis (DTA). The crystallization activation energies were determined by using variable heating rates in DTA. The chemical interaction studies of these glasses with Bi 4V 1.8Al 0.2O 11 electrolyte were also performed at 800 °C for different heat treatment durations. During chemical interaction in all the samples SrVSi 2O 7 phase has formed. However, its volume fraction depends on the chemical nature of the modifiers used in glass and duration of heat treatment. Apart from SrVSi 2O 7 phase, AVO 4 and A 2SiO 5 (A = Y, La, Al, Bi) phases are also present in the glass electrolyte interaction product mass. The formed phases were identified using X-ray diffraction. Fourier Transform Infrared (FTIR) spectroscopy has been done to identify the functional group and modification in bond structure and functional group with respect to the heat treatment duration in these samples. The results have been discussed on the basis of field strength of various cations and activation energy of crystallization.

Electrical conductivity of gamma-irradiated V 2O 5 doped lithium disilicate glasses doped and their glass–ceramics derivatives

Some physical properties of the lithium disilicate (Li 2Si 2O 5) glasses doped with different ratios of V 2O 5 were investigated before and after gamma-rays irradiation. Increasing V 2O 5 ratio causes remarkable changes in the properties studied. The observed variations in the properties may be correlated with the changes in internal glass network with changes in the chemical composition. Vanadium ions are believed to be present in three possible valence states V 3+, V 4+ and V 5+, and the ratios of these states depend on glass composition. Observed increase in electrical conductivity is assumed to be related to several parameters including the creation of localized state, which increase the charges carrier to conduction band, increase of the number of nonbridging oxygen’s and/ or electron hopping between vanadate ions in different valence states. However, the results indicate that the heat-treatment of amorphous samples accelerate the sequence of formation of lithium metasilicate crystals, causing a decrease in the electrical conductivity. The changes obtained due to gamma-irradiation are correlated to several factors, such as polarization and field strength of the respective cations and to the amount of induced defect centers created upon gamma-irradiation.

Influence of cationic field strength of modifiers on the 1.53 μm spectroscopic properties of Er 3+-doped tellurite glasses

Two series of Er 3+-doped tellurite glasses with different glass modifiers were prepared by the conventional melt-quenching method. In order to estimate the effect of cationic field strength z/ a 2 of modifiers on the fluorescence properties, the fluorescence spectra were measured. The strength parameters Ω t ( t = 2, 4, 6) for all the samples were calculated based on the absorption spectra and also compared between them. The values of Ω 6 decrease with decreasing of the cationic field strength z/ a 2 of modifiers. As the cationic field strength decrease, the polarization effect of the ligand fields around Er 3+ increase in the glasses, and which leads to the decreasing of fluorescence peak intensity and bandwidth. The strength of interactions between Er 3+ ions and OH − groups, k OH–Er, depend on the glass composition, are changed with glass modifiers.

The state of magnesium in silicate glasses and melts

The properties of silicate glasses and melts containing magnesium are analyzed in comparison with the properties of glasses and melts in which magnesium is replaced by aluminum. In particular, the properties of the glass and the melt of the diopside composition CaMgSi2O6 are analyzed in comparison with the properties of the glass and the melt of the anorthite composition CaAl2Si2O8. It is demonstrated that the properties of aluminosilicate and magnesium silicate glasses and melts differ not so strongly as should be expected upon replacement of modifier ions by network-former ions. By using the parameters γn characterizing the cation field strength, it is shown that Mg2+ cations can fulfill both the function of network formers like Al3+ cations and the function of modifiers like Ca2+ cations. The degree of depolymerization of the glass and the melt of the composition CaMgSi2O6 is estimated to be 0.4–0.5 from the dependences of the change in the relative density (d − d0)/d at different pressures on the degree of depolymerization NBO/T (the ratio of the number of nonbridging oxygen atoms to the number of network-former cations) for silicate glasses and the dependence of the isothermal bulk modulus Kt on the quantity NBO/T for silicate melts.

Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results

We examined aluminosilicate glasses containing a variety of network modifying to intermediate cations (Li, La, Sc, and Fe), quenched from melts at 1 atm to 8 GPa, to further investigate the role of cation field strength in Al coordination changes and densification. 27Al Nuclear Magnetic Resonance Spectroscopy (NMR) reveals that the mean Al coordination increases with increasing pressure in the Li-containing glasses, which can be explained by a linear dependence of fractional change in Al coordination number on cation field strengths in similar K-, Na-, and Ca-containing aluminosilicate glasses (K < Na < Li < Ca). Measured recovered densities follow a similar linear trend. In contrast, the La-containing glasses have significantly lower mean Al coordination numbers at given pressures than the cation field strength of La and glass density would predict. La L 3 X-ray absorption fine structure (XAFS) spectroscopy results indicate a significant increase with pressure in average La–O bond distances, suggesting that La and Al may be “competing” for higher coordinated sites and hence that both play a significant role in the densification of these glasses, especially in the lower pressure range. However, in Na aluminosilicate glasses with small amounts of Sc, 45Sc NMR reveals only modest Sc coordination changes, which do not seem to significantly affect the mean Al coordination values. For a Li aluminosilicate glass, 17O MAS and multiple quantum magic angle spinning (3QMAS) NMR data are consistent with generation of more highly coordinated Al at the expense of non-bridging oxygen (NBO), whereas La aluminosilicate glasses have roughly constant O environments, even up to 8 GPa. Finally, we demonstrate that useful 23Na and 27Al MAS NMR spectra can be collected for Ca–Na aluminosilicate glasses containing up to 5 wt.% Fe oxide. We discuss the types of structural changes that may accompany density increases with pressure and how these structural changes are affected by the presence of different cations.

Effects of cation field strength on the structure of aluminoborosilicate glasses: High-resolution 11B, 27Al and 23Na MAS NMR

Among the most important adjustable compositional variables in controlling glass and glass-melt properties are the relative proportions of network modifiers with varying cation field strength (ratio of charge to radius). Here we determine the details of structural changes caused by variations in the ratio CaO/Na2O in two series of aluminoborosilicate glasses with different contents of boron oxide. Using high-resolution, high field 11B and 27Al MAS NMR, we report precise values of contents of three- and four-coordinated boron (N4) and of four- and five-coordinated aluminum ([5]Al), and calculate fractions of non-bridging oxygens (NBOs). Increasing CaO/Na2O dramatically lowers N4 and increases NBO and [5]Al, but effects are non-linear with composition. Boron content affects these trends because of energetic constraints of mixing of various network cations. 23Na spectra reveal slight but systematic increases in the mean Na–O distance with increasing CaO/Na2O, suggesting that in Ca-rich glasses, Na+ has a higher ratio of bridging to non-bridging oxygens in its coordination shell. All of these changes can be understood by the tendency of higher field strength modifier cations to promote the concentration of negative charges on non-bridging oxygens in their local coordination environment, systematically converting four- to three-coordinated boron.

Probing and modeling of pressure-induced coordination transformation in borate glasses: Inelastic x-ray scattering study at high pressure

Here, we report on the in situ synchrotron inelastic x-ray scattering spectra of Na-borate glasses at high pressure up to 25 GPa. The pressure-induced boron coordination transformation from $^{[3]}\text{B}$ to $^{[4]}\text{B}$ is linear with pressure characterized by a single value of ${(\ensuremath{\partial}\text{ }^{[3]}\text{B}/\ensuremath{\partial}P)}_{T}$. Previous studies of Li-borate and pure-borate glasses show a nonlinear transformation with multiple ${(\ensuremath{\partial}\text{ }^{[3]}\text{B}/\ensuremath{\partial}P)}_{T}$ values for different pressure ranges, revealing the important role cation field strength plays in densification and pressure-induced structural changes. Considering the distribution of the energy difference between low- and high-pressure states $(\ensuremath{\Delta}\ensuremath{\epsilon})$ in the energy landscape and the variance of the ratio $\ensuremath{\Delta}\ensuremath{\epsilon}$ to its pressure gradient ${(\ensuremath{\partial}\ensuremath{\Delta}\ensuremath{\epsilon}/\ensuremath{\partial}P)}_{T}$ as a measure of network flexibility with pressure, an amorphous system with a large variance in $\ensuremath{\Delta}\ensuremath{\epsilon}$ at 1 atm and/or a small ${(\ensuremath{\partial}\ensuremath{\Delta}\ensuremath{\epsilon}/\ensuremath{\partial}P)}_{T}$ may undergo a gradual coordination transformation (e.g., Na borates). In contrast, a system with the opposite behavior (e.g., Li borates) undergoes an abrupt coordination transformation. The results and concepts of this study thus can shed light on opportunities to study the effect of composition on the nature of densification in low-$z$ oxide and other archetypal glasses and melts.

Oxygen-17 Nuclear Magnetic Resonance Study of the Structure of Mixed Cation Calcium−Sodium Silicate Glasses at High Pressure: Implications for Molecular Link to Element Partitioning between Silicate Liquids and Crystals

The structure of silicate glasses and the corresponding liquids at high pressure and their structure-property relations remain difficult questions in modern physical chemistry, geochemistry, and condensed matter physics. Here we report high- resolution solid-state O-17 3QMAS NMR spectra for mixed cation Ca-Na silicate glasses quenched from melts at high pressure up to 8 GPa. The spectra provide the experimental evidence for the varying pressure-dependence in two different types of nonbridging oxygen (NBO) environments (i.e., Na-O-Si and mixed (Ca,Na)-O-Si) in the single glass composition. The percentage of NBO drops significantly with increasing pressure and is a complex function of melt composition, including cation field strength of network modifying cations. A decrease in NBO fraction with pressure is negatively correlated with the element partitioning coefficient between crystals and liquids at high pressure.