Development of thermally stable tellurite glasses designed for fabrication of microstructured optical fibers

We optimize the composition of tellurite glass for the manufacture of photonic crystal fibers with a large spectrum of transparency. The glasses, synthesized in four and five component (TeO₂-WO₃-Na₂O-Nb₂O₅ and TeO₂-WO₃-PbO-Na₂O-Nb₂O₅) oxide systems with variable contents of WO₃ (5-38 mol%) and PbO (0-18 mol%), are designed and manufactured, and the transmission properties of the obtained glasses for the spectral range of 200 nm-7 μm have been determined. Thermal expansion coefficients and glass characteristic temperatures are determined by the dilatometer and Leitz heat microscope methods. Differential Scanning Calorimetry (DSC) measurements as well as crystallization tests by isothermal heat treatment are used to measure the thermal stability of the glasses and their ability to crystallize. Diffractive X-ray (XRD) measurements are used to determine the crystalline phases of the glass samples and the glasses with the highest resistance to recrystallization during thermal treatment were selected and used for the manufacture of photonic crystal fibers.     

Halide glasses

Halide glasses comprise a relatively uncommon class of inorganic glass systems which have heretofore been considered mainly as laboratory novelties. Serious attempts to develop these systems have generally been lacking owing to both difficulties in fabrication as well as because of the toxicity and chemical instability of some of these glasses. While halide glasses based upon beryllium fluoride and zinc chloride are well-known, the glass forming ability of ZrF₄, AlF₃, HfF₄, and more recently PbF₂ have also been demonstrated. The purpose of this review is to assess the technical and scientific importance of these glass systems, particularly with respect to advances within the past ten years.     

Halide glasses

The reasons for the formation of vitreous materials in halide systems are discussed in relation to the nature of the chemical bond. A review of fluoride, chloride, bromide and iodide glasses is presented and discussed in terms of stability and technical interest. The most interesting physical properties, especially optical, include the potential of ultra-low loss fiber for power and telecommunications applications. Recent structural investigations by X-ray, computer simulation, etc, allow the presentation of structural models explaining the glass formation by references to the corresponding crystalline halide materials. A structural systematic is described and compared with the traditional oxide glasses.     

Glassy states: Concentration glasses and temperature glasses compared

The behavior of glass-forming systems in the equilibrium state above the glass temperature is still a heavily investigated field. Surprisingly, the behavior of the glass itself is less widely investigated. Even less investigated is the behavior of glass-forming materials in which composition is changed. Here we look at the behavior of glasses after temperature-jumps and compare that behavior with that of glasses subjected to concentration-jumps. Moisture and carbon dioxide are used as the plasticizing environments. Surprisingly, the glass created by jumping (down) to a given final condition via a change in concentration is more stable than that formed by a change in temperature – this in spite of the external condition of temperature and chemical activity (RH or carbon dioxide pressure) being the same. Furthermore, the concentration glass under such conditions has a higher excess volume than the temperature glass and its response does not ‘merge’ with that of the temperature glass, hence, the concentration glass is not the same as a temperature hyperquenched glass.     

Development of novel ternary tellurite glasses for high temperature fiber optic mid-IR chemical sensing

The properties of novel ternary tellurite glasses, based on the TeO₂–BaO–Bi₂O₃ system, are reported for their applications in on-line chemical sensing and process control by characterizing the fundamental frequencies of molecular vibrations in the 2–5 μm spectral region of mid-IR. The chemical sensing for process control also requires above room temperature operation (>100 °C) for prolonged periods of time. Bulk samples of ternary tellurite glasses with a number of different compositions were prepared using heavy molecular weight oxides of TeO₂, BaO, and Bi₂O₃. Infrared and Raman spectroscopic analysis was carried out together with differential thermal analysis to study the relationship between glass structure and thermal and viscosity properties. The temperature dependence of the viscosities of the glasses is also reported. The compositional dependence of Raman frequency shifts and the corresponding change in the coordination of Te–O structure is discussed. The results from the IR edge, reflection spectroscopic, and wavelength dependence of refractive index are also reported.     

Attractive sulfonamide bridging bonds constructing lanthanide centered photoactive covalent hybrids

A new kind of sol–gel derived organic–inorganic hybrid material was prepared for the first time.In this case the organic portion of an acylamine derivation grafted by 3-aminopropyl trimethoxysilane and covalently linked together via sulfonamide linkages. Fourier transform infrared (FTIR), in ultraviolet absorption (UV) spectra and ¹H nuclear magnetic resonance (NMR) spectra were used to confirm these modifications and the X-ray diffraction (XRD) spectra were used to determine the framework. The material’s phosphorescent spectra and luminescence spectra were recorded. An efficient intramolecular energy transfer process between acylamine and lanthanide ions took place within these molecular-based hybrids. Strong green and red emissions were achieved for Tb³⁺ and Sm³⁺ ions, respectively.     

Lattice vibrations of glasses

Measurements of the thermal conductivity of glasses have led to a model of their lattice vibrations. They are not described as waves, as they are in crystals, but as uncorrelated harmonic motions of individual atoms. The lattice vibrations of fully cerammed, crystalline glass ceramics have been found to be either waves, as in crystals, or vibrations of individual atoms, as in glasses. The understanding of the cause for this different behavior has been aided by studies of systematically doped crystals.     

Crystallization of gel-derived glasses

The crystallization behaviors of gels, gel-derived glasses and melted glasses are reviewed, and comparisons are effected among the observed behaviors. These comparisons are related to the behavior expected on the basis of models for the nucleation frequency and crystal growth rate, as well as the anticipated differences in material characteristics among gels and the two types of glasses. Different temperature regimes are identified where different comparisons between melted and gel-derived materials are expected. It is concluded that a need exists for more definitive, detailed data on the crystallization behavior of gel-derived materials.     

Optical spectra of glasses

This presentation focuses on several ways in which structural and dynamical information can be obtained from optical spectroscopy by examining results of infrared and Raman studies of selected oxide glasses. Though these studies represent only a small fraction of the work on most of the glasses mentioned, and many other important forms of optical spectroscopy are not treated here, they illustrate useful approaches to the study of amorphous materials by optical methods.     

Lanthanum fluorozirconate glasses

Investigations in the ZrF₄-BaF₂-LaF₃ ternary system show the existence of a vitreous area in the range: ZrF₄: 56–67%, BaF₂:25–36%, LaF₃:3–13%. For a standard glass of molar composition 0.62 ZrF₄, 0.30 BaF₂, 0.08 LaF₃, the refractive index is 1.5248 with the glassy transition occuring at 310°C and fusion occuring at 545°C.Quaternary glasses have been obtained by including a MF fluoride (M = Na or Li) with the previous ternary glass according to the formula: (0.62 – 0.4x)ZrF₄(0.30 –0.5x)BaF₂(0.088 – 0.1x)LaF₃xMF. Evolution of glassy transition, refractive index, density and molar refractivity is discussed in relation to the structural role of the Na⁺ and Li⁺ ions. In these zirconium fluoride glasses, lithium could act as a network former at low concentration and as a network modifier at higher concentration.     

Stress-strain-acoustic emission response of glasses

Using the response of stress-strain-acoustic emission the microcrack behavior of ordinary and tempered glasses has been studied. As a result the authors propose two new concepts, the degree of microfracture and the damage ratio, which can be used as indications of material strength.     

EPR study of molybdenum-lead-phosphate glasses

The local symmetry and interaction between paramagnetic ions in xMoO₃(1 ? x)[2 P₂O₅PbO] glasses with 0.5 ? x ? 50 mol% are investigated by EPR spectroscopy. For x ? 10 mol% the isolated Mo⁵⁺ ions surrounded by five oxygen ligands in a square-pyramidal form (C_4v symmetry) prevail. The short range disorder in the environment of Mo⁵⁺ ions is not significantly (ΔR/R ≈ 2%). At high molybdenum content (x > 20 mol%) the dipole–dipole and superexchange coupled Mo⁵⁺ ions appear and their number increases with the MoO₃ content. These two aspects are also correlated with the network modifier and former role of molybdenum oxide in function of its concentration. Thus a strong depolymerization of the phosphate structure and the formation of P–O–Mo or Mo–O–Mo bonds in studied glasses appear.     

Structural analysis of bioactive glasses

In this study four series of single and mixed alkali glass systems were made and investigated using MAS NMR. Additionally the densities of the glasses were measured experimentally, as well as calculated theoretically using Doweidar’s model. MAS NMR was used to obtain a quantitative structural understanding of glasses by calculating the concentrations of bridging and non-bridging oxygens per silicon oxygen tetrahedron as a function of the alkali oxide concentration expressed as Qⁿ. ²⁹Si MAS NMR spectra exhibited a single resonance corresponding closely with Si in a Q² state. The chemical shift of the ³¹P MAS NMR peak was attributed to phosphate in an orthophosphate environment. The ²⁹Si NMR spectra are in agreement with the density data. Using Doweidar’s model the proportions of Q² and Q³ were calculated, showing that all glasses studied are predominantly Q² in structure, i.e. silica chains which readily dissolve. The changes in the chemical shifts of the Q² and Q³ species with composition have been interpreted as resulting from the preferential association of Na⁺ with Q³ and Ca²⁺ with Q².     

Aging of oriented polymer glasses

Dimensional (D) and enthalpy relaxation (ΔH) of oriented polymer glasses (PS and PC) have been studied as function of temperature, between T_g and T_g−20 °C, and aging time t, ranging to several weeks. The dimensional relaxation (shrinkage) and enthalpy relaxation curves verify the logarithm law D(t) ∼ H(t) ∼ log t, between an incubation τ_i and a final relaxation time τ_f. The time τ_f to reach the equilibrium (D and ΔH) follows the Vogel–Tamann–Fulcher (VFT) law. Enthalpy relaxation and shrinkage exhibit important differences. Enthalpy relaxation of oriented and isotropic polymers follows the same logarithm law, independent of the draw ratio λ and the mode of deformation, the relaxation time τ_f coincides with the relaxation time of the α segmental motions. Shrinkage depends on λ and the mode of deformation, the relaxation time τ_f is attributed to the normal mode, the relaxation time of the whole chain. Finally the shrinkages of PS and PC show some differences. PC at short aging times presents another type of dimensional relaxation which would be due to the β motions. This would be in close connection with the ductile (PC) and fragile (PS) behavior of these two polymers far below T_g.     

Electrical properties of phosphate glasses

The electrical properties of glasses in the Na₂OP₂O₅, Ag₂OP₂O₅ and (1?x)Na₂OxAg₂OP₂O₅ systems have been measured over a range of temperature and composition.The properties of the Na₂OP₂O₅ and Ag₂OP₂O₅ glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na₂O?xAg₂O?P₂O₅ system was found around the mole ratio of 0.16:0.84 Ag₂O:Na₂O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the T_g-against-composition plots. A linear relationship was noted for the tan δ-versus-log₁₀ (resistivity) plot, as has been seen in other glass-forming systems.     

Development of quaternary Fe-based bulk metallic glasses with high saturation magnetization above 1.6 T

Quaternary Fe-based ferromagnetic bulk metallic glasses (BMGs) with saturation magnetization above 1.6 T were successfully fabricated in Fe–Si–B–P alloy system by copper mold casting. These BMGs exhibit low coercive force of 1.6–1.9 A/m, high effective permeability of 16,500–17,200 and low core loss. In additional, these BMGs exhibit good mechanical properties as well, i.e., high strength of 3200 MPa and plasticity of 1.1%. They are promising to be used as magnetic functional and structural materials in the future.     

Internal friction of alkaline-earth-iron-metaphosphate glasses

The internal frictions of Mg, Ca, Ba iron-metaphosphate glasses were studied from 120 to 700 K using the low-frequency torsion pendulum technique. The internal friction as a function of temperature revealed two distinct peaks. The low-temperature peak was absent in glass without iron oxide. Its activation energy compared favourably with that for dielectric loss and dc conductivity in similar glasses. This suggests the same mechanism for all three processes, probably connected with electron transfer between iron ions of different valence.     

Structure analyses of Ba-silicate glasses

The structures of four different Ba-silicate glasses were analysed applying a broad spectrum of diffraction and spectroscopic methods, atomic force microscopy and computer simulations. This collaborative study offers new insights into the influence of the network modifier BaO. 3 at.% carbon were incorporated into two of the glasses with the intention to obtain additional information about the effect of partial substitution of carbon for oxygen on the considered structures. A structure model for Ba-silicate glasses with compositions close to BaSi₂O₅ is discussed that differs with respect to other models proposed in previous studies. We propose that [SiO₄] tetrahedra do not exclusively form six-membered rings, but also considerable numbers of smaller rings arranged in (slightly) folded layers which alternate with barium layers and/or barium chains. Additionally, the occurrence of tetrahedral chains, possibly isolated rings and of regions in which the [SiO₄] tetrahedra form a silica-like network is assumed.     

Infrared conductivity of chalcogenide glasses

The general features of the conductivity spectra of chalcogenide glasses in the frequency range 10⁹ to 10¹³ Hz are briefly reviewed.