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.     

Conversion of tin and alkali chlorides to phosphates and vitrification into silicate glasses

Mixtures of tin(II) chloride and tin(II)-sodium–potassium chlorides were converted into phosphate salts by reaction with ammonium dihydrogen-phosphate at 400 °C. Element analyses showed that no loss occurred during the treatment, and Mössbauer and wet analyses indicated no change in tin valence. The converted tin phosphate and tin–sodium–potassium phosphates were then dissolved into silicate glasses at 1350 °C without loss. Structural analyses were realized with ³¹P, ²⁹Si, ¹¹⁹Sn NMR and ¹¹⁹Sn Mössbauer, which revealed a complete dissociation of tin phosphate into the silicates. Phosphate units consisted in ortho- and pyro-phosphates. Tin(II) was partially oxidized into tin(IV), but there was no evidence for a phase separation into SnO₂ or SnP₂O₇, tin being mainly bonded to silicate units. These results are discussed in terms of O²⁻ exchange between phosphate and silicate units during the melting process.     

Bulk metallic glasses based on ytterbium and calcium

We report the formation of a family of bulk metallic glasses (BMGs) based on rare earth element of ytterbium and alkaline earth element of calcium. The glass-forming ability, atomic packing density and corrosion behaviors of the BMGs show an extremum around the eutectic point with the change of the concentration of Yb and Ca.     

Tantalum based bulk metallic glasses

Ta-based bulk metallic glasses with high strength (2.7 GPa) and hardness (9.7 GPa), high elastic modulus (170 GPa) and high density (12.98 g/mm³) were developed. The best glass forming ability so far for a Ta-Ni-Co system reaches a critical diameter of 2 mm by the copper mold casting method. It shows an exceptionally high glass transition temperature of 983 K and a high crystallization temperature up to 1023 K. The unique mechanical and physical properties make them a promising high strength material.     

New fluoride glasses based on 4f and 5f elements

New fluoride glasses have been isolated in the ternary systems ThF₄-LnF₃-BaF₂ with Ln = the lanthanides Yb, Y, Tm. The melt must be quenched to reduce crystallization. They are simply prepared from oxides by an appropriate NH₄F, HF treatment. The IR transmission is remarkable, the optical window lying in the 0.25-10 μm region.     

Bulk metallic glasses based on binary rare earth elements

Bulk metallic glasses (BMGs) are usually based on single element such as Zr, Cu, and Fe. In this work, we report the formation of a series of BMGs based on arbitrarily selected binary rare earth elements. Compared with single-base BMGs, the binary-base BMGs have unique characteristics of excellent glass-forming ability, tunable physical, chemical and mechanical properties. The binary-base BMGs might be of significance in scientific studies and have potential applications, and the approach for formation of metallic glasses has implications in the search for new BMG systems.     

Rare earth based bulk metallic glasses

Recently, the rare earth based bulk metallic glasses (REBMGs) have attracted increasing interest due to their unique properties and potential applications as functional glassy materials. These REBMGs display many fascinating properties such as heavy fermion behavior, thermoplastic properties near room temperature, excellent magnetocaloric effect, hard magnetism, and polyamorphism, all of which are of interest not only for basic research but also for metallurgy and technology. These characteristics and properties are ascribed to the unique electronic, magnetic and atomic structures of the REBMGs. In this review paper, the fabrication, glass-forming ability, polyamorphism, elastic, thermal, and physical properties are summarized and discussed. Owing to the unique electronic structure of rare earth elements, the electric and magnetic properties of the REBMGs are especially addressed. The works have implications for seeking novel metallic glasses with controllable properties and for understanding the nature of glass formation. The development of REBMGs as functional materials might promote and extend the commercial applications of metallic glasses.     

Erbium doped fiber and highly non-linear fiber based on bismuth oxide glasses

Extend L-band amplification, high gain C + L-band amplification for coarse wavelength division multiplexing and short pulse amplification can be realized using bismuth based erbium doped fiber. On the other hand, step-index type fiber using bismuth based glass whose refractive index of 2.22 at 1.55 μm is fabricated. This fiber exhibits high non-linearity (γ = 1360 W^?1 km^?1) because of the high non-linearity of the glass material and the small effective core area.     

Pb(II)-ion-selective electrodes based on chalcogenide glasses

Novel chalcogenide glasses (ChG) from the GeSe₂-PbSe-PbTe system were investigated as membrane materials in ion-selective electrodes reversible to Pb(II)-ions. Pb(II)-ion-selective electrodes (Pb(II)-ISE) of ‘coated wire’ type were constructed, which consist of standard Ag/AgCl electrodes uniformly coated with a composite mixture of polymer filled with GeSe₂-PbSe-PbTe glassy powder. The basic analytical characteristics of Pb(II)-ISE, such as reproducibility, linear range (L), slope of the electrode function (S), limits of detection (LD), working pH-range and response time (τ₉₅), were studied with respect to the ChG composition. The cross-selectivity in the presence of some interfering ions, which commonly attendant Pb²⁺-ions in analytical media, was investigated. Potential-generating mechanism was suggested explaining sufficiently the observed dependencies.     

Bulk metallic glasses based on rare-earth elements in lanthanum series

A series of bulk metallic glasses (BMGs) based on the rare-earth (RE) elements in lanthanum family have been obtained by a copper mold casting method. These chemical comparable RE elements with ‘continuous’ range of atomic size, electron structure and elastic constants may provide a good system for systematically exploring the BMG-forming characteristics. The glass-forming ability, elastic properties, thermal stability and their correlations in the RE-based BMGs have been investigated.     

Characteristics of composites based on PMMA modified gel silica glasses

Gel silica glass prepared by the sol-gel process can be modified by incorporating an organic phase into the intrinsically porous inorganic gel matrix, which results in a composite material with much improved mechanical and optical properties. Characterisation of PMMA modified gel silica glass prepared by the in situ polymerisation method using FT-Raman spectroscopy, gel permeation chromatography and the nitrogen adsorption technique are reported. Some essential problems encountered in the preparation are discussed.     

Lutetium and thulium based rare earth bulk metallic glasses

We report the formation of lutetium and thulium based bulk metallic glasses based on the correlations between the thermodynamic, kinetic, elastic and other properties of metallic glasses. The two novel rare earth based bulk metallic glasses (REBMGs) exhibit excellent glass formation ability, high elastic moduli, considerable smaller Poisson’s ratio, high thermal stability, and even higher mechanical strength than that of typical high strength Zr-based BMGs. The reasons for the properties of the Lu- and Tm-based and other REBMGs are discussed.     

Self refractive non-linearities in chalcogenide based glasses

We report third order non-linear absorption and refraction measurements at 1.20 and 1.52 μm on selected gallium-Lanthanum sulfide-based glasses (Ga:La:S) showing negligible non-linear absorption and a refractive non-linearity close to one hundred times that of SiO₂. Their potential use in telecommunication as base materials for all-optical switching practical devices is evaluated resulting in large figures of merit. The addition of a glass modifier to the Ga:La:S matrix has improved thermal and optical properties, resulting in ease of fibre drawing. The non-linear optical response of this new variant of the Ga:La:S family is studied.     

Molecular dynamics,diffraction and EXAFS of rare earth phosphate glasses compared with predictions based on bond valence

Rare earth (RE) phosphate glasses, (R₂O₃)_x(P₂O₅)_1−x, commonly form with x < 0.3. As previously discussed by Hoppe, in this composition range Q² groups provide 6 O_nb (non-bridging oxygens) per RE, but higher RE coordinations can occur if RE are bonded to O_nb on Q³ groups, or if RE–O_nb–RE configurations occur (where Qⁿ refers to a PO₄ tetrahedra with connectivity of n). The values of N_RO and R_RO from the majority of the previous diffraction and EXAFS studies of RE phosphate glasses have been surveyed. Overall, the experimental results for 0.18 ⩽ x ⩽ 0.28 indicate RE coordination is from 6.5 to 7.0 for large RE, and slightly lower for small RE. For x ⩾ 0.23 this implies the occurrence of RE–O_nb–RE configurations, as observed in recent diffraction studies. The experimental results for x ⩽ 0.15 indicate RE coordination is from 7.5 to 8, which can be attributed to RE bonding to O_nb on Q³ groups. RE coordination of 8 for x ∼ 0.15 requires 2 Q³ groups (per RE) to be connected to Q² groups. Comparison with estimated connectivities between Q² and Q³ groups indicate that chemically ordered Q²–Q³ linkages are required. A recent MD model of a Tb metaphosphate glass has N_RO = 6, but includes Tb bonded to O_nb on Q³ groups and Tb–O_nb–Tb configurations, because it has a broad Qⁿ distribution.     

Photoinduced structural changes in antimony polyphosphate based glasses

A photocontraction effect in amorphous films of the binary glass system 0.20 [Sb(PO₃)₃]_n–0.80 Sb₂O₃ has been observed after UV irradiation using the 350.7 nm Kr⁺ ion laser line with 5.0 W/cm². Good optical quality films up to 4.0 μm were deposited on silica substrates at room temperature in vacuum by electron beam physical vapor deposition (EB-PVD) and characterized using WDX, XRD, optical absorption, infrared reflectance, profilometry and atomic force microscopy (AFM) techniques. Very stable glasses were prepared by the melt quenching technique and used as evaporation source for the production of films. The photoinduced structural change (PSC) was observed as a variation of about 6% in the film thickness and this effect is accompanied by a photobleaching of the irradiated area with a blue shift of the optical absorption edge. Otherwise this photoinduced change in the film thickness is very sensitive to the variations in the shape and intensity of the laser beam; therefore several possibilities in optical recording arise from these results.     

Raman spectroscopic study of bioactive silica based glasses

A study of the structure and bonding configuration of the bioactive glasses in the system Na₂O–CaO–P₂O₅–SiO₂ by Fourier transform Raman spectroscopy is presented. The assignment of the Raman lines, the changes in the Si–O–Si bond environment and the identification of the non-bridging silicon–oxygen groups (Si–O–NBO) for a wide range of silicate glasses are discussed. The frequency shifting and intensity variations of the Raman lines as a function of the bioactive glass composition are attributed to a decrease of the local symmetry originated by the addition of alkali and alkali earth oxides to the vitreous silica network. Correlation plots for the quantification of the Si–O–NBO groups as a function of the glass composition are also presented. These Raman analyses contribute to a better knowledge of the structural role of the network modifiers in the bioactive glasses and, as a consequence, improve the understanding of the bioactive process and the chemical routes of the CaP layer formation when exposed body fluids.     

Evaluation of glass-forming ability for bulk metallic glasses based on characteristic temperatures

A new criterion ω₂, defined as T_g/(2T_x?T_g)?T_g/T_l (wherein T_g is the glass transition temperature, T_x the onset crystallization temperature, and T_l the liquidus temperature), has been proposed to assess the glass-forming ability (GFA) of bulk metallic glasses (BMGs) based on the classical crystallization theory and the crystallization resistance. The analysis indicates that the factors T_g/(2T_x?T_g) and T_g/T_l could reflect the crystallization resistance and liquid phase stability of metallic glasses, respectively. From the available experimental data in literatures, the new criterion ω₂ has a better correlation with the GFA of metallic glasses than all other existing criteria such as T_rg(=T_g/T_l), ΔT_x(=T_x?T_g), γ(=T_x/(T_g+T_l)), ΔT_rg(=(T_x ? T_g)/(T_l ? T_g)), α(=T_x/T_l), β(=T_x/T_g + T_g/T_l), δ(=T_x/(T_l ? T_g)), φ(=T_rg(ΔT_x/T_g)^0.143), γ_m(=(2T_x ? T_g)/T_l), β(=T_x × T_g/(T_l ? T_x)²) and ξ(=ΔT_x/T_x+T_g/T_l). It has also been demonstrated that this ω₂ parameter is a simple and efficient guideline for exploring new BMG formers.