Number Of Non-bridging Oxygen Ions Research Articles

Microstructure and electrical conduction of iron-doped barium titanate glass-ceramics

Glasses with the mol % composition 20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3 were synthesized. During heat treatment at 550°C for 5 min to 7 h, cubic BaTiO3 crystallized. The microstructure of the glass-ceramics was studied by scanning electron microscopy. The average size of the crystalline particles varied from 190 to 790nm, depending on the crystallization time. Impedance measurements of selected glass-ceramics at temperatures from -183 to 97°C using frequencies from 100Hz to 1MHz witness insulating properties. The ac-conductivity at 100Hz increases with temperature from 10−10 S/m at -183°C to 10−6 S/m at 97°C. The ac-conductivity is established predominantly in the glass phase with Na+-ions as charge carriers and could be well fitted by the universal as well as by the modified Jonscher power law. However, for the intermediate temperature range, the modified Jonscher equation seems to better explain the physical mechanisms of conduction dispersion with frequency. In the whole studied temperature range, the power “s” in the dispersion equation slightly varies with the glass-ceramics’ thermal history but shows a relatively large decrease with increasing temperature. The higher conductivity of the sample with the highest BaTiO3 volume fraction is associated with the lowest s-value and largest number of non-bridging oxygen ions in the structure.

Structural behavior of F− in mould flux melt of CaO-SiO2-Al2 O3-Na2 O-CaF2 system

The influence of fluorine on the structure of CaO-SiO2-Al2O3-Na2O-CaF2 continuous-casting-type slag was measured by Raman spectroscopy, and the degree of polymerization of mould flux and the structural behavior of F− in the melt were investigated by classifying and quantifying the structural species of F− ions. The results exhibit that the main structural units of Si-O tetrahedra are Q0, Q1 and Q2 and the actual measured number of non-bridging oxygen ions in the [SiO4]-tetrahedra (denoted by NBO/T) increases from 2. 73 to 3. 44 with increasing the molar ratio of F to (F+O) (denoted by XF/X(F+O)) from 0. 06 to 0. 19. It means that the degree of polymerization of melt structure decreases with an increase in XF/X(F+O). In addition, most of F− ions were distributed in Si-O tetrahedra and Al-O tetrahedra. With increasing XF/X(F+O), the complex structural units Al-O tetrahedra are gradually replaced by discrete structural units AlF1– because of the breakage of Al-O bonds in Al-O tetrahedra by F− ions, and the Si-O (bridging oxygen) bonds of Si-O tetrahedra are broken to form [SiOnF1–n]-tetrahedra by F− ions coordinating with Si4+.

Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined from the IR spectra after deducing the relative absorption coefficient of boron tetrahedral versus boron trigonal units, α = α4/α3, using NMR literature data of the diamagnetic glasses.

Plasticity, crack initiation and defect resistance in alkali-borosilicate glasses: From normal to anomalous behavior

We provide a comprehensive description of the defect tolerance of sodium-borosilicate glasses upon sharp contact loading. This is motivated by the key role which is taken by this particular glass system in a wide variety of applications, ranging from electronic substrates, display covers and substrates for biomedical imaging and sensing to, e.g., radioactive waste vitrification. The present report covers the mechanical properties of glasses in the Na2O–B2O3–SiO2 ternary over the broad range of compositions from pure SiO2 to binary sodium-borates, and crossing the regions of various commercially relevant specialty borosilicate glasses, such as the multi-component Duran-, Pyrex- and BK7-type compositions and typical soda-lime silicate glasses, which are also included in this study. In terms of structure, the considered glasses may be separated into two groups, that is, one series which contains only bridging oxygen atoms, and another series which is designed with an increasing number of non-bridging oxygen ions. Elastic moduli, Poisson ratio, hardness as well as creep and crack resistance were evaluated, as well as the contribution of densification to the overall amount of indentation deformation. Correlations between the mechanical properties and structural characteristics of near- and mid-range order are discussed, from which we obtain a mechanistic view at the molecular reactions which govern the overall deformation reaction and, ultimately, contact cracking.

IR, UV–vis spectroscopic and DSC investigations of europium doped tellurite glasses obtained by sol–gel synthesis

FTIR, UV–vis spectroscopy and DSC studies were utilized in order to study structural changes produced by the variation of the Eu(NO3)3 content in binary europium–tellurite glasses obtained using the sol–gel method. Our results show that the europium ions can be considered as modifiers because they will produce the transformation of [TeO4] and [TeO6] structural units into [TeO3] trigonal pyramidal units and the formation of a significant number of non-bridging oxygen ions.UV–vis studies show that the higher Eu(NO3)3 concentrations (24mol%) in the host matrix induce a growth of the number of 4f–4f electronic transitions of the Eu+3 ions and a increase of the number of non-bridging oxygen ions in the regions between 325 and 600nm.In brief, partial replacement of TeO bonds by EuO ionic bonds induces a global weakening of the network explaining the decrease of the glass transition temperature and crystallization temperature by gradually increasing of europium ions in the matrix network.

Effect of aluminum oxide codoping on copper–lead–germanate glasses

Glasses from xCuO⋅(100-x)[7GeO2⋅3PbO2⋅0.05Al2O3] system where x=0, 1, 5, 10, 20 and 30mol% CuO were studied by FT-IR, UV–VIS and ESR spectroscopy in order to obtain information about the structural correlations and the relationship between structure and optical properties in these materials. The analyses of these IR spectra reveal that the accommodation of the network with the excess of oxygen ions is possible by the depolymerization of the germanate network in shorter chains, especially ortho- and/or pyrogermanate structural units.UV–VIS absorption spectrum of the sample with x=1% CuO begins with a rising absorption band situated at about 250nm. This band can be assigned to the GeOGe wrong bonds such as the Ge+2 centers. Optical study is performed to calculate the refractive index and optical band gap using UV–VIS spectra in the wavelength range 250–1000nm. The increase in optical band is explained on the basis of the average bond energy of the system and the number of non-bridging oxygen ions. ESR spectra of CuO substituted samples are characterized by broad peaks probably because of the formation of Cu+2–Ge+2 exchange pairs which are weakly coupled though the oxygen atom.

RAMAN STUDY OF xMeO · (100-x)[P2O5 · CaO](MeO=Fe2O3, V2O5 OR (Fe2O3 · V2O5)) GLASS SYSTEMS

Glasses from x MeO · (100-x)[ P 2 O 5 · CaO ], ( MeO = Fe 2 O 3, V 2 O 5 or ( Fe 2 O 3 · V 2 O 5)) were prepared and investigated using Raman scattering spectroscopy, over compositional range x=0–50% mol. The influence of Fe 2 O 3, V 2 O 5 or ( Fe 2 O 3· V 2 O 5) content on the structure of P 2 O 5· CaO glass matrix was followed. The addition of Fe 2 O 3, V 2 O 5 or ( Fe 2 O 3· V 2 O 5) determines the modification of the structure of the studied glasses. The Raman spectra of x Fe 2 O 3(100-x)[ P 2 O 5· CaO ] do not present any absorption bands characteristic to Fe 2 O 3 but its evolution is dependent on the iron content. The Raman spectra of x V 2 O 5·(100-x)[ P 2 O 5· CaO ] present, besides the bands specific for the matrix, some bands assigned to characteristic vibrations of V – O bonds which are evidenced only for high content of V 2 O 5. The evolution of the spectra is dependent on V 2 O 5 content. The Raman spectra of x( Fe 2 O 3· V 2 O 5)·(100-x)[ P 2 O 5· CaO ] system showed that phosphate units are the main structural units of the glass system, iron and vanadium ions are located in the network. The increasing of iron and vanadium content indicate a gradual decrease in the number of bridging oxygen ions and an increase in the number of non-bridging oxygen ions.

Influence of iron ions on the structural and magnetic properties of some zinc-phosphate glasses

Glasses in the (Fe 2O 3) x ·(P 2O 5) 40·(ZnO) 60− x (0 ≤ x ≤ 30 mol%) system have been prepared by the melt-quenching technique. The structural and magnetic properties of these glasses were investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The XRD pattern for the prepared samples shows their vitreous state only for x ≤ 20 mol%. For the samples containing 30 mol% Fe 2O 3 the presence of a unique crystalline phase, FePO 4, embedded in an amorphous matrix was evidenced. FTIR spectroscopy data suggest that the iron ions play the network modifier role in the studied glasses. The addition of iron oxide leads to the breakage of P O bonds and the formation of the P–O–Fe bonds. The presence of the Fe–O–P bonds for the samples with higher iron oxide content in the studied system improves their chemical durability. The increases of iron ions content of the samples determine a gradual decrease in the number of bridging oxygen ions respectively the increase of the number of non-bridging oxygen ions. EPR and magnetic susceptibility measurements show the presence of the Fe 3+ ions in sites of distorted octahedral symmetry and as well as in clustered formations containing both Fe 3+ and Fe 2+ ionic species. Dipolar and superexchange interactions involving iron ions were revealed depending on the iron content of the sample.

Investigation of spectroscopic properties and thermal stability of Er 3+/Yb 3+-co-doped Bi 2O 3–B 2O 3–Ga 2O 3 glasses

A series of Er 3+/Yb 3+-co-doped 60Bi 2O 3–(40− x) B 2O 3 – xGa 2O 3 (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er 3+: 4I 13/2 level and thermal stability were measured and investigated. Three Judd–Ofelt intensity parameters Ω t ( t=2,4,6) ( Ω 2=(4.67–5.93)×10 −20 cm 2, Ω 4=(1.50–1.81)×10 −20 cm 2, Ω 6=(0.92–1.17)×10 −20 cm 2) of Er 3+ ions were calculated by Judd–Ofelt theory. It is found that the Ω 6 first increases with the increase of Ga 2O 3 content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section ( σ e peak = 0.83 - 1.03 × 1 0 - 20 cm 2 ) of Er 3+: 4I 13/2→ 4I 15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69–76 nm) of the 4I 13/2→ 4I 15/2 transition of Er 3+ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers.

Volume of ionic sites in silicate glasses

Molar volume data of alkali and alkaline earth silicate glasses have been used tocalculate the free volume associated with the bridging and nonbridging oxygen andmodifier ions. The free volume associated with the bridging oxygen is constant(15.39 × 10−24 cm3) for all modifier ions up to 33.3 mol% modifier oxide. It decreases (in alkali or alkaline earthsilicate glasses) with increasing number of nonbridging oxygen ions per structural unit and/orradius of the modifier ion. The nonbridging oxygen ion is associated with a constant free volume(6.50 × 10−24 cm3) in all cases. Modifier ions are associated with free volume that increases with increasingnumber of nonbridging oxygen ions per structural unit and/or radius of the modifier ion.The used model explores the change in the free volume due to changing the concentrationof alkali oxides in mixed alkali silicate glasses. The results show that, in such glasses, thefree volume related to a certain type of alkali oxide increases with increasing content.

Thermal conductivity of CaO–SiO2–Al2O3 glassy slags: Its dependence on molar ratios of Al2O3/CaO and SiO2/Al2O3

Thermal conductivities of CaO–SiO2–Al2O3 glassy slags have been determined using the nonstationary hot wire method as functions of (mol.-%Al2O3)/(mol.-%CaO) and (mol.-%SiO2)/(mol-%Al2O3) ratios over a temperature range 300–1270 K. The thermal conductivities of the samples investigated were in the range between 1·0 and 1·6 W m−1 K−1. The thermal conductivities of samples having a constant concentration of SiO2 increased with increasing the (mol.-%Al2O3)/(mol.-%CaO) ratio as long as the constant pressure heat capacity per unit volume was kept constant. This increase in thermal conductivities would be due to increases in the speed of sound and/or the phonon mean free path by re-polymerisation of the network structure of silicate glasses by Al2O3. On the other hand, the thermal conductivities of samples having a constant value of NBO/T (the ratio of the number of non-bridging oxygen ions per tetrahedrally coordinated cation) decreased with increasing the (mol.-%SiO2)/(mol.-%Al2O3) ratio. This decrease in thermal conductivities would be dominated by the constant pressure heat capacities per unit volume of the samples.

Spectroscopic properties and thermal stability of Er 3+-doped TeO 2–B 2O 3–Nb 2O 5–ZnO glass for potential WDM amplifier

A series of novel 70TeO 2–(15 − x)B 2O 3– xNb 2O 5–15ZnO–1 wt.% Er 2O 3 (TBN x = 0, 3, 6, 9, 12 and 15 mol%) tellurite glasses were prepared. The thermal stability, absorption spectra, emission spectra, and the lifetime of the 4I 13/2 level of Er 3+ ions were measured and investigated. Three Judd–Ofelt intensity parameters Ω t ( t = 2, 4 and 6) ( Ω 2 = (5.42–6.76) × 10 −20 cm 2; Ω 4 = (1.37–1.73) × 10 −20 cm 2; Ω 6 = (0.70–0.94) × 10 −20 cm 2) of Er 3+ ions were calculated by Judd–Ofelt theory. It is found that the Ω 6 first increases with the increase of Nb 2O 5 content from 0 to 6 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section ( σ e peak = ( 0.77 – 0.91 ) × 10 − 20 c m 2 ) of Er 3+: 4I 13/2 → 4I 15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM = 65–73 nm) of the 4I 13/2 → 4I 15/2 transition of Er 3+ ions were measured. The results indicate that these new TBN glasses can be used as a candidate host material for potential broadband optical amplifiers.

STRUCTURAL STUDY OF x(Fe2O3·V2O5)·(100-x)[P2O5·Li2O] GLASS SYSTEM BY FTIR SPECTROSCOPY

Glasses of the x( Fe 2 O 3· V 2 O 5)·(100-x)[ P 2 O 5· Li 2 O ] system, with 0≤x≤50 mol %, were prepared and investigated by FTIR spectroscopy in an attempt to determine the local structure of glasses. The interpretation of the obtained IR spectra revealed the presence and the dependence of the local structural units in the studied glasses on the iron and vanadium ions content. The results showed that phosphate units are the main structural units of the glass system and the iron and vanadium ions are located in the network. The increasing of iron and vanadium ions content indicate a gradual decreasing in the number of bridging oxygen ions and an increasing in the number of nonbridging oxygen ions.

Raman study on B 2O 3–CaO glasses

Glasses are of special interest nowadays mainly because of the large applications that they span. Raman spectroscopy is an experimental technique appropriate for providing information about the structure of local arrangements of the atoms in glasses. The influence of CaO content on the structure of borate glasses was investigated by Raman spectroscopy. At low calcium oxide content the structure of calcium borate glass consists mainly of boroxol groups and a smaller number of pentaborate groups. In the vitreous network there are few diborate groups, chain type metaborate groups and pyroborate groups. At high calcium oxide content, pentaborate, orthoborate and metaborate groups appear. The increase of calcium oxide content yields an increase in number of non-bridging oxygen ions. Therefore, we conclude that calcium ions act as network modifiers in borate glasses.

Refractive index-structure correlations in Na 2O–Al 2O 3–SiO 2 glasses

The current structural models have been used to analyse the refractive index data of Na 2O–Al 2O 3–SiO 2 glasses (Al 2O 3/Na 2O⩽1). The SiO 2 content is the sole factor that controls the refractive index. Values could be obtained for the factors with which each structural unit contributes in the refractive index. The content of Al 2O 3 or Na 2O has no effect on the refractive index. The factors (differential refraction) are constant and do not change with composition. They have the same values for Na 2O–SiO 2 glasses. The differential refraction of a structural unit increases linearly with increasing the number of non-bridging oxygen ions. The difference of the contribution to the refractive index from a silicate unit to the next equals to a half of that for AlO 4 tetrahedron. The effect could be attributed to the change in both the concentration and differential refraction of structural units. The obtained factors for the structural units are useful in calculating the refractive index with a high degree of accuracy.

Refractive index–structure correlations in silicate glasses

A model has been presented to correlate the refractive index with the structure of CaO–SiO 2, SrO–SiO 2, BaO–SiO 2 and related ternary glasses. A quantitative analysis of the property-composition dependence has been carried out. Any of the structural units present in these glasses has a specific ability (the differential refraction) to refract the light. The differential refraction depends only on the type of the modifier oxide, but not on its concentration. It increases linearly with the increase in the number of non-bridging oxygen ions in the structural unit. The differential refraction for a structural unit in ternary silicate glasses remains the same found for the corresponding binary glasses. On the basis of the structural units distribution, relations are given to calculate the refractive index as a function in composition for the binary- or the mixed-modifier silicate glasses. The results indicate that the refraction of light is the result of interaction between the waves and the structural unit as a whole rather than with the ions separately.

Density-structure correlations in silicate glasses

A quantitative analysis has been carried out for the density data of CaO–SiO 2, SrO–SiO 2, BaO–SiO 2 and CdO–SiO 2 glasses. The analysis is based on a model that has been applied for alkali silicate glasses. The model makes it possible to calculate the volumes of the structural units and to plot the density-composition dependence for these glasses. The results show that CaO, SrO, BaO and CdO enter the structure as modifiers. The volume of a structural unit changes with the type, but not with the concentration, of the modifier. The volume increases linearly with the increase in the reciprocal of the field strength of the modifier ion. A linear dependence could be observed for alkali and alkaline earth silicate glasses. A general relation has been obtained to calculate the volume of the structural unit as a function of the radius and charge of the modifier ion and the number of non-bridging oxygen ions (NBOs).

Applicability of Molecular Dynamics to Analyses of Refining Slags.

By the use of molecular dynamics simulation (MD), varieties of properties including structural, transport, optical and thermodynamic properties can be calculated. Since this feature is very attractive to the analyses of refining slags, its applicability was studied. CaO-SiO2 melts with CaO contents ranging from 40 to 60 at% were simulated at 1873 K. The calculated pair distribution functions and general tendency of silicon ion fractions with various number of non-bridging oxygen ions agreed well with experiments reported elsewhere. The calculated diffusion coefficient of every ion as a function of CaO content was also in good agreement with the measured values. These demonstrate the promising applicability of MD to slag analyses.The melt of 45at%CaO-45at%SiO2-10at%CaF2 was also simulated by MD to study the effects of fluorine addition to silicate melt. The hypothesis of the existence of di-fluorine ions in some thermodynamic modeling of slags was not verified due to the lack of appropriateness of the interatomic potentials used in this study.

Comparative study of the effect of the incorporation of cobalt and nickel oxides on the density and optical properties of copper tellurite glasses

Two series of ternary semiconducting glasses with composition 65 TeO2-(35−x)CuO-xMO in mole percent (x=0, 0.5, 1, 2, 3, 4 and M stands for Co or Ni) were prepared by a melt quenching technique. The densities of annealed and unannealed disc-shaped samples and the optical energy gap of thin blown films of both series of glasses were measured, and the comparative effect of each transition metal (TM) oxide was estimated. It was found that forx=0.5 to 1 mol% andx=2 to 4mol%, the optical energy gap (Eopt) was somewhat greater in TeO2-CuO-NiO than in TeO2-CuO-CoO glasses. This increase inEopt is interpreted in terms of the decreasing number of non-bridging oxygen ions with the increase of each TM oxide. NiO was found to be more effective in increasing the density than CoO in annealed copper tellurite glasses.