Glass formation and structure of Na2SSiO2 and Na2SB2O3 glasses

Glass-forming regions of the systems Na₂SSiO₂ and Na₂SB₂O₃ have been investigated in order to clarify whether Na₂S could be substituted for Na₂O in sodium silicate or borate glasses, and the results were interpreted in terms of the structures of silicate and borate glasses. No difference was found in the glass-forming range of SiO₂ content between the Na₂SSiO₂ and Na₂OSiO₂ systems, and the red color of Na₂SSiO₂ glasses suggests that the formation of polysulfides in the glass structure is probably due to the entrance of sulfur ions in the non-bridging sites of the glass network. On the other hand, not all of the sulfur added to the glass batches could be retained in the Na₂SB₂O₃ glasses and the amount remaining in the glass products changed depending upon the amount of sodium ions in the glasses. Only a trace of sulfur was observed in the glasses containing less than 13 mol% of Na₂S in the batches, but the sulfur content in the glasses increased steeply with sodium content up to 35 mol%, reached the maximum and then decreased slowly with sodium content. The insolubility of sulfur in the glasses with low sodium content was interpreted based on the compositional dependence of basicity of alkali-borate glasses, and the change in solubility of sulfur with sodium concentration was explained based on the well-known boron anomaly caused by the change in the coordination state of boron and on the formation of non-bridging oxygens or sulfurs in the glass structure.     

Nuclear magnetic resonance studies of the glasses in the system Na2OB2O3SiO2

The ¹¹B NMR spectra have been used to study the structure of glasses in the system Na₂OB₂O₃SiO₂. The fraction of BO₄ units, and the fraction of BO₃ units with one or two nonbridging oxygens, are measured and analyzed according to a structural model. The results indicate that: (1) for a sodium oxide to boron oxide ratio of 0.5 or less, the Na⁺¹ ions are attracted primarily by the borate network; therefore, the ternary glasses can be viewed as binary sodium borate glasses diluted by SiO₂; (2) when the sodium oxide to boron oxide ratio exceeds 0.5, the additional Na₂O results in the formation of [BSi₄O₁₀]^?1 units at the expense of diborate and SiO₄ units. In this process, Na⁺¹ ions are still taken up only by the borate network. After all the available SiO₄ units are consumed to form [BSi₄O₁₀]^?1 units, additional Na⁺¹ ions are proportionally shared between the borate and silicate networks.     

A neutron small angle scattering study of SiO2Na2 O glasses

The first results obtained by small-angle neutron scattering (SANS) study of sub-liquidus immiscibility of glasses are presented. Measurements were performed on the neutron small-angle scattering spectrometer of the Institut Laue-Langevin (Grenoble, France). The glass studied was 0.88 (SiO₂), 0.12 (Na₂O) from SiO₂Na₂O system which presents a well-known miscibility gap already explored by small-angle X-ray scattering (SAXS) method. Absolute values of the neutron scattering cross section as a function of scattering vector were obtained for this glass quenched and heat treated at 560°C for various lengths of time. It is shown that the ANS method can be used to follow phase separation kinetics and the comparison with SAXS results can in principle be used to separate the effects of density and concentration fluctuations in this system.     

Glass formation and structure of glasses in B2O3―Bi2O3―MoO3 system

The purpose of this paper is to study the glass formation tendency in the ternary system B₂O₃―Bi₂O₃―MoO₃ and to define the main structural units building the amorphous network. A wide glass formation area was determined which is situated near the Bi₂O₃―B₂O₃ side. A liquid phase separation region was observed near the MoO₃―B₂O₃ side for compositions containing below 25 mol% Bi₂O₃ and their microheterogeneous structure was observed by SEM. The phase formation was characterized by X-ray diffraction (XRD). By DTA was established the glass transition temperature (T_g) in the range of 380-420 °C and crystallization temperature (T_x) vary between 420 and 540 °C. The main building units forming the amorphous network are BO₃ (1270 and 1200 cm^− 1), BO₄ (930-880, 1050-1040 cm^− 1), MoO₄ (840-760 cm^− 1) and BiO₆ (470 cm^− 1). It was proved that Bi₂O₃ favors the BO₃ → BO₄ transformations while MoO₃ preserves BO₃ units in the amorphous network.     

The leaching behavior of PbOSiO2 glasses

The leached layer of PbOSiO₂ glasses formed by diluted nitric acid solution has been investigated by ellipsometry and Auger electron spectroscopy (AES). The leaching behavior of PbOSiO₂ glasses in 10^?4 N aqueous solution of NHO₃ at 30°C was measured in real time using a Nikon auto-ellipsometer.The results were applied by curve fitting to the two-layer model from the concentration profile obtained by AES, and the refractive index profile against the film thickness was determined.The leached layer is inhomogeneous and consists of a low refractive index region and a transition region. The gradient of the refractive index in the former region is extremely small and the refractive index becomes nearly constant between 1.42 and 1.44. The shape of latter region becomes stable with its thickness at 100–310 Å, and moves in the direction of depth without changing the shape as the leaching proceeds.     

EPR study of crystalline and vitreous forms of the Li2OAl2O3SiO2 system

The epr spectra of V⁴⁺ and radiation centres have been studied in β-eucryptite (LiAlSiO₄), β-, γ-spodumene (LiAlSi₂O₆) and in glasses prepared by the fusion of the single crystals. It is shown that the electronic structures of the vitreous state in the Li₂OAl₂O₃SiO₂ system and that of the crystalline forms differ considerably. The change of the electronic structure on crystallization is not direct, but is realized through the intermediate state whose electronic structure differs from that of glasses and crystals.     

11B and 27Al NMR studies of glasses in the system Na2OB2O3Al2O3 (“NABAL”)

¹¹B and ²⁷Al nuclear magnetic resonances (NMR) in glasses of the NABAL system Na₂OB₂O₃Al₂O₃ have been studied as a function of composition. From the boron data, the fraction of four-coordinated BO₄ units has been determined via computer analysis of the NMR spectra; the method is similar to that employed previously for binary and other ternary borate glasses. The ²⁷Al NMR indicates no abrupt change in the average aluminum environment. Certain linear relationships have been found which yield detailed information on the competing processes of BO₃, BO₄ and AlO₄ formation, and the formation of triclusters consisting of three tetrahedra having one oxygen in common. Furthermore, it is concluded that the oxygen available for the formation of various aluminum-containing species is a function of the soda concentration only and that the conversion to AlO₄ is favored as compared with BO₄.     

ESR and optical absorption of Cu2+ in Na2OSiO2 glasses

ESR and optical absorption spectra of Cu²⁺ in xNa₂O(100?x)SiO₂ glasses were measured, where x ranges from 12 to 70 mol% Na₂O. This glass system was divided into three composition regions, 12 ? x ? 37, 37 ? x ? 55 and 55 ? x, from the composition dependence of the ligand field transition energy and spin hamiltonian parameters of Cu²⁺. Two boundary compositions (37 and 55 mol%) between the two adjacent regions agreed with the eutectics in the equilibrium phase diagram. Two types of Cu²⁺-complexes, with less basic ligands (HFS-1) and much more basic ones (HFS-2), were detected in ESR for ultra-high soda glasses (x ? 55). The distribution of the ESR parameters due to the fluctuation of ligand fields was negligible for HFS-2 compared with that for other glasses. The Cu²⁺ ion responsible for HFS-2 was considered to distribute in the microphase of orthosilicate. Imagawa's basicity, the covalency of the bondings between Cu²⁺ and ligands, was calculated by using Maki and McGarvey's analysis. The basicity of σ-type symmetry remained constant, irrespective of the glass composition, and the value was identical with those for other oxyanionic glasses. The π-type basicity was also constant for the glasses of x ? 55. Two different basicities, each corresponding to HFS-1 or 2, were obtained for the glasses of x ? 55. The value derived from HFS-1 was identical with those for x < 55 glasses, whereas that derived from HFS-2 suggested the formation of much more basic ligands.     

Small polaron conduction in V2O5P2O5 glasses

Dc conductivity measurements have been made between 90 and 520 K on three bulk samples of V₂O₅P₂O₅ glass. Heat treatment is found to result in a reduction of the activation energy at a given temperature and this is most noticeable at low temperatures. The behaviour at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours. At intermediate temperatures a simple model is used in which excitations by optical and acoustic phonons are considered to make independent contributions to the jump frequency. Mott's theory is extended to the polaron case for $\text{T>}\text{1}\text{4}\text{?}$ and is shown to be in good agreement with results. Values for $\text{r}{}_{\mathrm{<mtext>p</mtext>}}\text{(～2.8}\text{A}\text{?}\text{)}$ the polaron radius and $\text{α(～3.5}\text{A}\text{?}{}^{\mathrm{?1}}\text{)}$ the electron decay constant are shown to be consistent with the model for small polarons. A method is suggested for obtaining α and N(E_F) from the ac conductivity and the slope of 1nσ versus $\text{1}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ at low temperatures. Values of N(E) are obtained which correlate with those obtained by the previous analysis. This implies that the disorder energy separating adjacent sites Δ₀ is large (～0.4 eV) in these materials.     

Electronic structure and properties of oxide glasses (II) Basicity measured by copper(II) ion probe in Na2OP2O5, K2OB2O3 and K2SO4ZnSO4 glasses

The correlation between the basicity of oxygens measured by the Cu(II) ion probe and the non-bonding electron density on oxygens in alkali borate glasses was considered. The basicity was measured for K₂OB₂O₃, Na₂OP₂O₅ and K₂SO₄ZnSO₄ glasses and categorized into two types, δ and π, according to the symmetry property of the bonding between a Cu(II) ion and oxygen. The π basicity for borate and phosphate glasses showed an abrupt increase in the vicinity of 17 and 50 mol% alkali oxide, respectively. The values of π-type basicity varied with the composition of glass, being larger in the order: sulfate < phosphate ? borate, whereas δ basicity was constant irrespective of the glass composition. Such a change of the basicity with the composition of glass was interpreted in terms of behavior of non-bonding levels of the ligand oxygens in a glass network.     

Electrical conductivity and photoconductivity of As2S3PbS glasses

Measurements of dc electrical conductivity and photoconductivity of various glassy compositions (x = 0.1?0.625) in (As₂S₃)_1?x(PbS)_x have been made. Experimental results of the temperature dependence of dc conductivity from room temperature to 200°C (which includes the glass transition temperature) are reported. All the compositions exhibit intrinsic conduction in the measured temperature range. Thermal activation energy, glass transition temperature and σ₀ for the compositions studied, were determined from the experimental data. The low value of $\text{σ}{}_0\text{(10?10}{}^{\mathrm{?2}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$) in these semiconducting glasses is attributed to the greater participation of localized states in the conduction process.In the measurements of photoconductivity, the variation of photocurrent with temperature, photon energy, light intensity and electric field is observed. The recombination model has been involved to explain the results of photoconductivity. Both electrical and photoconductivity data support the presence of higher density of localized states in the x = 0.1 composition than in others.     

Glasses and glass-ceramics from naturally occurring CaOMgOAl2O3SiO2 materials (I) glass formation and properties

Once oil is extracted from oil shales, the inorganic solid which remains is from the CaOMgOAl₂O₃SiO₂ system. The material is easily melted and forms a glass upon cooling. Its viscosity in the forming region is actually less than that of commercial soda-lime glass. Shale glasses exhibit excellent dielectric behavior, while their other properties are generally comparable to commercial glasses. These glasses appear to be promising materials for future applications.     

Crystallization and phase-separation of Li2OSiO2 glass

The crystallization and phase-separation phenomena in the Li₂OSiO₂ glass are studied by positron lifetime and annihilation lineshape measurements. Analysis of the kinetic data shows three-dimensional morphology of growing crystals. Phase-separation is seen to increase the density of crystal nuclei and the rate of volume crystallization, but it does not affect the morphology. In addition, surface crystallization is detected in glasses with small degrees of phase-separation. The results are consistent with scanning electron and optical micrographs.     

Infrared spectra and structure of superionic conducting glasses in the system AgIAg2OMoO3

Thin blown films of glasses with the mole ratio Ag₂O/MoO₃ = 1 in the system AgIAg₂OMoO₃ (or the pseudobinary system AgIAg₂MoO₄) show three absorption bands in the range 4000-200 cm^?1; 875 cm^?1 (w), 780 cm^?1 (s), and 320 cm^?1 (m, b), which are characteristic of tetrahedral MoO₄^2? ions. The glasses with the ratio Ag₂O/MoO₃ < 1 have two additional bands at 600 cm^?1 (w) and 450 cm^?1 (vw), which are characteristic of condensed ions of MoO₄ tetrahedra, probably Mo₂ O₇^2? ions. These glasses are thus composed of Ag⁺, I^?, MoO₄^2?, and probably Mo₂O₇^2? ions, and classified as “ionic” glasses containing one type of cations. The presence of partial covalency in the Ag⁺… ^?OMo link and the influence of ion exchange of Ag⁺ with K⁺ on IR spectra are discussed. The molar volume of the glasses with the ratio Ag₂O/MoO₃ = 1 is primarily determined by a fairly dense packing of the constituent anions, I^? and MoO₄^2?.     

Semiconducting TiO2SiO2 glasses (I): Electronic conductivity

Semiconducting glasses, 70% TiO₂-30% SiO₂, with a Ti³⁺ content varying from zero to 7.8%, have been prepared by rf sputtering in argon/oxygen/hydrogen gas mixtures. Conduction in the Ti³⁺-containing glasses is by small polarons hopping adiabatically. The disorder energy is small (0.05 eV) compared to the hopping energy (0.37–0.51 eV). The variation of the hopping energy with Ti³⁺ content and temperature is ascribed to a polaron overlap effect and to effects arising from the random glass structure, respectively. At low temperatures conduction is a percolation process. The conduction in Ti³⁺-free glasses is not due to polarons; at low temperature these glasses exhibit variable-range hopping.     

Photoconductivity of oxychalcogenide glasses in the system As2Se3CdO

The photoconductivity of oxychalcogenide glasses in the system As₂Se₃CdO was investigated. When 2–3 mol % CdO was added, the photoresponse peak of the parent glass As₂Se₃ in the vicinity of 740 nm became broader and a little weaker. The addition of more than about 4 mol % CdO brought about a sharp and strong peak at 720 nm and a broad peak at 860 nm. X-ray diffraction and electron microscopic observations revealed the presence of crystalline CdSe in the glass matrix, indicating that the reaction As₂Se₃ + 3CdO → As₂O₃ + 3CdSe took place in the melting process of these glasses. Tempeature and light intensity dependences of the photocurrent lead to the conclusion that the above spectral photoresponse is greatly affected by the presence of the dispersed crystalline CdSe.     

Phase separation in GeGeO2 glasses

De Neufville prepared homogeneous glasses ranging in composition from pure GeO₂ to GeO by quenching bulk samples from the melt and by vapor deposition. For compositions in the range of 10–20 mol % excess Ge dissolved in GeO₂, he found that phase separation into amorphous Ge rich and amorphous GeO₂ phases occurred. The results reported here on a 7.5 mol % excess Ge composition using differential scanning calorimetry have shown that a two-step phase separation mechanism is operative. A homogeneous GeGeO₂ glass phase separates at 450°C into amorphous GeO₂ and amorphous GeO. The GeO phase separates at 570°C into crystalline Ge and amorphous GeO₂. The heat measured at 570°C is equal to the sum of the heats of phase separation of GeO and crystallization of Ge. The amorphous GeO₂ crystallizes at 670°C with a heat of crystallization of 4.65 kcal/mol (± 0.5). Additional support for a two-step phase separation mechanism is provided by kinetic arguments based on the viscosity dependence on composition and on the structure of the amorphous GeO phase and its stability relative to the homogeneous GeGeO₂ glass.     

Short range antiferromagnetic ordering in vitreous Fe2O3P2O5

An outline is given of the theory of neutron magnetic scattering from amorphous materials, and data are presented for vitreous 0.79 Fe₂O₃ · P₂O₅. The magnetic correlation function shows that at low temperatures the glass exhibits short-range antiferromagnetic ordering with Fe³⁺?Fe³⁺ interionic distances similar to those found in crystalline FePO₄. The neutron data are not consistent with a previous suggestion that the material is microcrystalline.     

The effect of different alkali ions on the optical and magnetic properties of R2O−B2O3 + MnO2 glasses

Spectrophotometric, magnetic studies and chemical analyses of a number of binary alkali borate glasses containing manganese were carried out in order to throw some light on the structure of these glasses and on the forms in which manganese exists in borate glasses.The results obtained could be explained on the basis that manganese exists in glasses in two different states; divalent manganese coordinated with tetrahedral arrangements with oxygen and shows four bands at about 400, 460, 490 and 530 nm with very low molecular extinction coefficients, and trivalent manganese assuming octahedral symmetry having a broad band at 470–500 nm which under some conditions shows splittings to two or three peaks with high values of molecular extinction coefficients.The paramagnetic character of the glasses containing manganese is usually attributed to the presence of five and four unpaired electrons in the divalent and trivalent states of manganese, respectively. The ratio of trivalent to divalent manganese ions depends on several factors, including the polarisability of the oxygen ligands surrounding the manganese ions, the presence of bridging and non-bridging oxygen and the type of alkali ion present.     

Glass formation and structure of glasses in the ZnO―Bi2O3―WO3―MoO3 system

The glass formation region in the ternary ZnO―Bi₂O₃―WO₃ system is determined by melt quenching technique (cooling rates 10¹-10² K/s). New original glasses are obtained in a narrow concentration range with high WO₃ content (60-75 mol%). Homogeneous glasses of the composition (100 − x)[0.2ZnO·0.3Bi₂O₃·0.5WO₃]xMoO₃, were obtained between 20 and 60 mol% MoO₃. Characterization of the amorphous samples was made by x-ray diffraction (XRD), differential thermal analysis (DTA) and infrared spectroscopy (IR). The thermal stability of glasses decreases with the increasing of MoO₃ content. The glass transition temperature, T_g, varies between 340-480 °C, while the crystallization temperature, T_x, varies between 388-531 °C. The tungstate glasses possess higher crystallization temperature (T_x over 500 °C) in comparison with the other vanadate and molybdate non-traditional glasses. The glass network is realized by transformation of three-dimensional structure of WO₃ into a layered one, consisting mainly of WO₆ units. We supposed that the network of quaternary glasses is built up by MoO₄, MoO₆ and WO₆. At low concentration ZnO and Bi₂O₃ facilitate the disorder in the supercooled melts, while at high concentration stimulate crystallization processes. These oxides belong to the intermediate ones.