Formation Of Non-bridging Oxygen Atoms Research Articles

Investigation of the optical properties of borosilicate glass recycled from high-pressure sodium lamp glass: Compositional dependence by addition of Bi2O3

We examined the effects of bismuth (III) oxide (Bi2O3) on the optical properties of glass. The glass samples were prepared with high-pressure sodium lamp glass as the initial material with different concentrations of Bi2O3. Optical properties such as the refractive index, optical band gap, Urbach energy, polarisability and metallisation were investigated. The results indicated that addition of Bi2O3 into the network structures of the glass samples increased the formation of non-bridging oxygen atoms. This resulted in a decrease of the optical band gap and an increase in the polarisability of the glass samples. The types of electron transitions were studied by comparison between the differential method and the Davis and Mott model. The results showed that the electrons moved directly by an allowed transition.

The structure of glasses of the LI2O-K2O-GEO2 system revealed by Raman spectroscopy

Glasses of the three-component system Li2O-K2O-GeO2 were studied by Raman spectroscopy. Peak-fitting of spectra on constituent lines is performed and the basic structural units formed in the system are determined. The conditions for the appearance of highly coordinated germanium atoms are determined, and non-statistical distribution of modifier cations in the studied glasses is found. It is shown that substitution of the lithium cations by potassium cations, firstly, results in a change of the coordination number of Ge atoms, and then a rupture of the Ge–O–Ge bonds with the formation of non-bridging oxygen atoms.

Synthesis and characterization of barium fluoride substituted zinc tellurite glasses

Glasses in the TeO2-ZnO-BaF2 system were prepared by standard melt quenching technique and were characterized for their thermal, optical and structural properties. Samples were found to show good thermal stability with values ranging above 100°C for all the compositions. Optical bandgap and refractive index values were calculated from linear optical measurements using UV-Vis spectroscopy. Infrared spectra showed the presence of hydroxyl groups in the glasses indicating that the effect of fluorine was negligible in removing the hydroxyl impurities for the experimental conditions and compositions used. Raman measurements showed the modification occurring in the glass network due to addition of barium fluoride in terms of increase in the formation of non-bridging oxygen atoms compared to strong Te-O-Te linkages in the glass matrix.

Surface and bulk electron irradiation effects in simple and complex glasses

A three oxide sodium borosilicate (BS3) and a complex, thirty oxide borosilicate glass (SON68) were irradiated with 2.3MeV electrons to doses ranging from 0.15GGy to 4.6GGy at 350K. The irradiated glasses were characterized using Raman and NMR spectroscopies, ToF-SIMS, AFM and microhardness to understand surface and bulk irradiation effects. Glass surfaces were observed to be depleted of the alkali atoms. The depletion depth depended on the dose and glass composition, reaching 660nm and 500nm on any vacuum facing surface for BS3 and SON68 at 4.6GGy respectively. The alkali-depleted region was enriched in molecular oxygen and showed characteristics of phase separated glasses. In the bulk of the glass, Raman and NMR spectroscopies showed a silica network depolymerisation, a transformation of 4 to 3-coordinated boron and formation of non-bridging oxygen atoms on silicon and boron atoms. The hardness of the depolymerized glasses decreased by 20% (BS3) and 10% (SON68). Based on the experiments and theory, it is shown that electron stimulated desorption is the dominant surface depletion mechanism. These results show that the surfaces behave differently than the bulk of the glass. Therefore, surface related phenomena are expected to be dominant in TEM and other in-situ and ex-situ surface characterizations having depth resolution of a few hundred nanometers. Thus, sample size plays an important role in evaluating the radiation damage and one must be careful in extending the conclusions drawn from surface sensitive techniques to bulk irradiation effects in electron irradiated glasses.

Optical band gap and structural study on GeO2- and Y2O3-doped barium aluminoborate glasses

A series of barium borate-based glasses containing Al2O3, GeO2 and Y2O3 were prepared by conventional method of glass melting and annealing. The prepared glasses were investigated through optical, FTIR, density and molar volume measurements. The optical absorption spectra reveal three characteristic UV absorption peaks at about 213, 240 and 308 nm. The optical absorption measurements were used to estimate direct and indirect transition of optical band gap (Eopt), Urbach energy (ΔE) and the refractive index (n).Values of the optical parameters are found to be related to the structural changes that are taking place in the prepared glasses. The deconvoluted vibrational modes identified in the IR spectrum illustrated the conversion of triangular BO3 structural units to BO4 tetrahedral units with the addition of GeO2 or Y2O3. The formation of non-bridging oxygen atoms is assumed to lead to provide some favorable properties, mainly the optical properties and semiconducting behavior of the prepared glassy samples. Density and molar volume data are found to be dependent on the rigidity of the glass network.

Physical, thermal, structural and optical absorption studies of vanadyl doped magnesium oxy-chloride bismo-borate glasses

Oxy-chloride bismuth-borate glasses with composition xMgCl2·(30 − x)MgO·20Bi2O3·50B2O3 containing 2 mol% doping of V2O5 (x = 12, 15, 20, 25 and 30) are prepared by melt-quenching technique. The structural, thermal and optical behaviors are explained by analyzing the data obtained from density (D), molar volume (Vm), theoretical optical basicity (Λth), differential scanning calorimetry (DSC), FTIR and UV–vis results. A decrease in D and increase in Vm (except for sample MBV3 for which D is maximum) on increasing chloride content suggests the formation of non-bridging oxygen atoms. Maximum glass transition temperature (Tg) and crystallization temperature (Tx) have been observed for sample MBV3. The glass stability (S) and stability ratio (S/Tg) have been calculated from the values of Tg and Tx and both are having maximum values for sample MBV3. Study of the FTIR spectra in the mid-IR range reveals the presence of both triangular and tetrahedral coordinated boron. The optical studies through UV–vis spectral analysis show non-sharp edge. The optical band gap (Eg) is also maximum for sample MBV3

Deeper insight on the lithium reaction mechanism with amorphous tin composite oxides

Lithium reaction mechanism in amorphous tin composite oxide SnB 0.6P 0.4O 2.9 is characterized by X-ray diffraction, 119Sn Mössbauer spectroscopy and X-ray absorption fine structure. The analysis of the experimental data concerning SnB 0.6P 0.4O 2.9 shows that Sn II is highly ionic and is surrounded by three oxygen atoms. The detailed analysis of lithium insertion mechanism shows a complex reduction mechanism in two steps. During the first one the main reaction corresponds to a partial Sn II reduction, involving a mixed valence system. It is accompanied by modifications of tin environments, while lithium acts as a network modifier inducing the formation of nonbridging oxygen atoms. The second step corresponds to LiSn alloying process, with the formation of LiSn bonds. It is worth noting the persistence of SnO interactions in this second step. The reversible part of the mechanism can be explained from the formation of small particles of lithium–tin alloys in strong interaction with the oxygen atoms in the glass matrix, while the vitreous support presents an interesting dispersal effect.

Structure and physical properties of glassy lead vanadates.

The structure and physical properties of the lead-vanadate glasses of compositions (${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$${)}_{\mathit{x}}$(PbO${)}_{100\mathrm{\ensuremath{-}}\mathit{x}}$ with x=50--90 mol %, prepared by the roller-quenching technique have been studied. It has been shown by x-ray diffraction, scanning electron microscopy, density and oxygen molar volume measurements, etc., that single-phase homogeneous glasses with a random network structure can be obtained in this system. The network structure is built up of unaffected ${\mathrm{VO}}_{5}$ groups as in crystalline ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ and affected ${\mathrm{VO}}_{5}$ groups. A gradual decrease in the coordination number of ${\mathrm{V}}^{5+}$ and ${\mathrm{V}}^{4+}$ ions and the formation of nonbridging oxygen atoms have been observed with increasing ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ content in the glass compositions, consistent with the decrease in density. The nearly equimolar glass composition devitrifies to crystalline metavanadate ${\mathrm{PbV}}_{2}$${\mathrm{O}}_{6}$. However, glasses with higher ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ content devitrify to ${\mathrm{PbV}}_{2}$${\mathrm{O}}_{6}$ and a ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$-rich amorphous phase. The fine structure of the electron spin resonance hyperfine lines observed when the glass composition is equimolar, gradually reduces to a two-component structure at the same effective g value and is interpreted as due to an increase of the hopping rate of polarons with increasing ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$ content in the glass compositions.

Borate glass structure by Raman and infrared spectroscopies

Raman and infrared spectroscopies have been employed to probe the continuous evolution of borate glass structures as a function of the nature and concentration of alkali oxide modifier. At relatively low alkali contents, the glasses contain covalent networks consisting of interconnected units bearing BO − 4 tetrahedra. Further addition of alkali oxide causes the progressive depolymerization of the network as a result of the formation of non-bridging oxygen atoms. Eventually, complete network disruption into small and highly charged borate units results in “ionic” glasses. The nature of the alkali cation determines the structure of these glasses by affecting several high- temperature isomerization or disproportionation equilibria.

A Linear Relationship between the Glass Transition Temperature and Local Distortion of Calcium Gallate, Barium Gallate, and Calcium Aluminate Glasses

Abstract The isomer shift in the 57Fe-Mössbauer spectra of xCaO·(90−x)Ga2O3·10Fe2O3 (x=40–60) and xBaO ·(90−x)Ga2O3·10Fe2O3(x=65–70) glasses decreases gradually from 0.28 to 0.16 mm s−1 with increasing CaO or BaO contents. This indicates a formation of nonbridging oxygen atoms in the GaO4 and FeO4 tetrahedra. Large quadrupole splitting (Δ) values ranging from 0.98 to 1.24 mm s−1 indicate a noticeable distortion of the GaO4 and FeO4 tetrahedra. Mössbauer parameters of xCaO·(95−x)Al2O3·10Fe2O3 glasses (x=55–60) are comparable to those of the xCaO·(90−x)Ga2O3·10Fe2O3 glasses, suggesting that the local structures are essentially the same with each other. The glass transition temperatures (Tg) of the calcium gallate, barium gallate, and calcium aluminate glasses are 702–728, 580–583, and 750–773 °C, respectively. It is found that the Tg of several oxide glasses is proportional to the Δ, being expressed by Tg=aΔ+b, where “a” is 680 °C mm1 s and “b” is −180°C when the Fe3+ ions are present at substitutional sites of the network former (NWF). The “Tg–Δ rule” is also applicable to the Fe3+ ions present at interstitial sites, in which case “a” and “b” are 35°C mm−1 s and 260°C, respectively. These findings indicate that the Tg is primarily determined by the distortion of NWF–oxygen polyhedra.

Structural Study of Na2O–TeO2 Glasses by Mössbauer Spectroscopy and Differential Thermal Analysis

Abstract A Mössbauer spectrum of xNa2O·(95−x)TeO2·5Fe2O3 glasses (0≤x≤35) consists of a paramagnetic quadrupole doublet peak with an isomer shift of 0.39±0.01 mm s−1 with respect to metallic iron. Quadrupole splitting of the doublet peak changes gradually from 0.76 to 0.60 mm s−1 when Na2O content is changed from 0 to 35 mol% at 5 mol% intervals. These results suggest that Fe3+ ions are present at substitutional sites of Te4+ ions constituting distorted TeO4 trigonal bipyramids. Each of the distorted TeO4 trigonal bipyramids has an oxygen vacancy and a lone electron pair at one of the equatorial sites. Decreased quadrupole splitting is ascribed to an increased symmetry of FeO4 (and also TeO4) trigonal bipyramids, due to a formation of nonbridging oxygen atoms followed by a gradual change of the glass matrix from a two-(β-TeO2) or three-(α-TeO2) dimensional network structure to a lower dimensional network structure. These structural changes are also deduced from a composition dependency of glass transition temperatures (Tg), which decrease continuously from 318 to 232 °C with increasing Na2O content.

Application of Mössbauer Spectroscopy to a Structural Study of Superionic Conducting AgI–Ag2O–B2O3 Glasses

Abstract A structural study of silver borate glasses containing 20 mol% AgI and 1 mol% 57Fe2O3 has been performed by Mössbauer spectroscopy. A Mössbauer spectrum of these glasses consists of an asymmetric quadrupole doublet with an isomer shift smaller than 0.4 mm s−1 with respect to metallic iron. This indicates that the individual Fe3+ ions are present at the substitutional sites of the tetrahedral boron atoms constituting BO4 units as a network former. An increase in the Ag2O content results in continuous decreases in the isomer shift and the quadrupole splitting when the Ag2O content exceeds about 16 mol%, which corresponds to the Ag2O/B2O3 ratio of 0.25 and the alkali oxide content of 20 mol% in the binary borate glasses. These results are ascribed to the formation of nonbridging oxygen atoms in the tetrahedral BO4 and FeO4 units. A glass transition temperature (Tg) of the glasses shows a distinct composition dependency, having a maximum around 16 mol% Ag2O. These lead to the conclusions that planar BO3 units are changed into the tetrahedral BO4 units in the lower Ag2O content region and that the nonbridging oxygen atoms are formed in the BO4 and FeO4 units when the Ag2O content is higher than 16 mol%. These conclusions are well consistent with the composition dependency of the electric conductivity which shows a minimum when the Ag2O content is 10–15 mol%.

Mössbauer and DTA Studies of Semiconducting Potassium Vanadate Glasses Containing Iron

Abstract A Mössbauer spectrum of a series of potassium vanadate glasses containing 10 mol% Fe2O3 shows a paramagnetic quadrupole doublet, of which isomer shift proves to be smaller than 0.4 mm s−1 with respect to metallic iron. This indicates that the individual Fe3+ ion is present at the substitutional site of the V5+ (and probably V4+) ion constituting a VO4 tetrahedral unit. An increase in the K2O content of the potassium vanadate glasses results in a continuous decrease in the glass transition temperature (Tg), ranging from 239 to 200 °C, when the K2O content is changed from 5 to 30 mol%. This suggests a decrease in the coordination number of the V5+ (and V4+) ion from 5 to 4 and a formation of nonbridging oxygen atoms in the VO4 and FeO4 tetrahedral units. The formation of nonbridging oxygen atoms in the VO4 and FeO4 units is also estimated from a continuous decrease in the quadrupole splitting, suggesting a decrease in the electric field gradient at the iron nucleus and an increase in the symmetry around the Fe3+ ion. These results lead to the conclusion that the introduction of the alkali oxide (K2O) into the V2O5 results in a structural change of the V5+ (and V4+) ions from VO5 tetragonal pyramid (or trigonal bipyramid) to VO4 tetrahedral units.

Structural Study of Germanate Glasses by 119Sn Mössbauer Spectroscopy

Abstract Mössbauer study of potassium germanate glasses containing a small amount of Sn4+ has been performed to know the relationship between the abnormal composition dependence of physical properties, so-called germanate anomaly, and the local structural change of the glasses. Distinct increases in isomer shift and linewidth and a distinct decrease in quadrupole splitting are observed when the concentration of alkali oxide exceeds about 16 mol%. These changes are ascribed to the formation of nonbridging oxygen atoms in GeO4 units. This is also supported by a drastic decrease in a parameter of intermolecular force constant obtained from the temperature dependence of Mössbauer absorption area. The composition dependence of the parameter is well consistent with that of glass transition temperature (Tg) of the same samples. Transformation of GeO4 tetrahedra into GeO6 octahedra is also confirmed by increases in the parameter of intermolecular force constant and in Tg in the alkali content region lower than 16 mol%. The role of Sn4+ is concluded to be a network modifier which is present at an interstitial site of three-dimensional network composed of GeO4 and GeO6 units.

ESCA study on the mechanism of adherence of metal to silica glass

Indium oxide films formed on the surface of silica glass samples by selective oxidation have been shown to greatly improve the adherence of gold-indium alloy to the silica glass. In order to clarify the role that the oxide films play in the reaction, thin indium films have been evaporated onto silica glass and heated at temperatures of between 973 and 1473 K, both in air and in hydrogen gas. Electron spectroscopy for chemical analysis (ESCA) measurements have then been made to investigate the chemical environments around oxygen and indium atoms at the reacting interface between the oxide and glass. Measured 01s and In3d5/2 spectra reveal the formation of non-bridging oxygen atoms at the interface, in addition to the original bridging oxygen atoms in silica glass. Introduction of the non-bridging oxygen atoms and indium ions into the silica glass is concluded to be an essential factor in promoting good adherence between the gold alloy and silica glass.