Thermo-optic properties of B2O3 doped Li2O-Al2O3-SiO2 glass-ceramics

Reduction in the temperature coefficient of the optical path length, dS/dT of Li₂O-Al₂O₃-SiO₂ glass-ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ?, and the thermal expansion coefficient, α. The dS/dT value of 2.6 mol% B₂O₃-doped glass-ceramic was 12.5  × 10⁻⁶/°C, which was 0.9 ×  10⁻⁶/°C smaller than that of B₂O₃-free glass-ceramic. On the other hand, reduction in dS/dT through B₂O₃ doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass-ceramic through B₂O₃ doping is caused by the reduction in ?. The reduction in ? from B₂O₃ doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ? value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B₂O₃-doped glass-ceramic crystallized under 196 MPa was 11.7 ×  10⁻⁶/°C. That value was slightly larger than that of silica glass. The α value of this glass-ceramic was smaller than that of silica glass.     

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

Tungstate fluorophosphate glass compositions with high WO₃ concentration were prepared in the ternary system (80−0.8x)NaPO₃-(20−0.2x)BaF₂-xWO₃ with x = 40,50 and 60 mol%. Transparency decreases as WO₃ concentration increases but can be improved by addition of oxidizing systems such as CeO₂ or Sb₂O₃/NaNO₃. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO₃ results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO₃ donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO₃ content and vitreous sample containing 60% of WO₃ exhibits an endothermic event around 620 °C due to crystallization of monoclinic WO₃ phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO₃ phase can be grown in such glasses.     

Effect of BaO content on the sintering and physical properties of BaO-B2O3-SiO2 glasses

A BaO-B₂O₃-SiO₂ glass system was chosen as a candidate composition for the application to Pb-free low temperature sinterable glass. The effect of BaO content on the crystallization, sintering behavior, and properties of the glasses was examined. Both the glass transition temperature and crystallization temperature decreased as the BaO content increased. Crystallization easily occurred during sintering with a BaO content of more than 50 mol%, which effectively inhibited the over-firing phenomenon. The dielectric characteristics and thermal expansion coefficient of the glasses were examined and the results were explained on the basis of the crystallization and densification of the specimens.     

Thermal and some physical properties of glasses in the La2O3−CaO−B2O3 ternary system

Glasses in the La₂O₃−CaO−B₂O₃ ternary system were studied. The glass forming range as determined by the appearance of the annealed cast was found to match previously published findings. Clear glasses were formed in the composition range of 5.7−19.1 mol% La₂O₃ with constant B₂O₃ content of 71.4 mol%, and in glasses of constant La₂O₃:CaO ratio of 1:4 with B₂O₃ content in the range of 71.4-55.0 mol%. The non-linear optical crystalline phase La₂Ca₂B₁₀O₁₉ was crystallized from the clear glasses after heat treatments, as determined by powder XRD. Two types of the LaBO₃ crystalline phases were detected in the partially and the fully crystallized glass compositions outside the glass forming range. Data are reported for the glass transition temperature (T_g), dilatometric softening point (T_d), linear coefficient of expansion (α), onset crystallization temperature (T_x), exothermal peak temperature (T_P), density (ρ) and index of refraction (n_D) in the clear glasses.     

Polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP)-based composite polymer electrolyte containing LiPF3(CF3CF2)3

This paper describes the preparation and characterization of lithium fluoroalkylphosphate-containing composite polymer electrolyte based on a polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) matrix. A mixture of ethylene carbonate and diethyl carbonate was used as a plasticizing agent and nanoscopic Al₂O₃ as a filler. The membranes were characterized by ac impedance, SEM, DSC, FTIR and fluorescence. An electrolyte with 2.5 wt% Al₂O₃ exhibited a conductivity of 9.8 × 10⁻⁴ S cm⁻¹ at ambient temperature. It was found that filler contents above 2.5 wt% rendered the membranes less conducting.     

Spectroscopic properties of Er-doped Na2O-Sb2O3-B2O3-SiO2 glasses

Spectroscopic properties of Er³⁺-doped Na₂O-Sb₂O₃-B₂O₃-SiO₂ glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er³⁺-doped 5Na₂O-20Sb₂O₃-35B₂O₃-40SiO₂ glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the ⁴I_13/2 → ⁴I_15/2 transition and the lifetime of the ⁴I_13/2 level of Er³⁺ ions are 6.8 × 10⁻²¹ cm² and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σ_e × FWHM, is as great as 598.4 × 10⁻²¹ cm² nm, which is comparable or higher than that of Er³⁺-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks.     

Effect of P2O5 content in two series of soda lime phosphosilicate glasses on structure and properties - Part II: Physical properties

The effect of the variation in phosphate (P₂O₅) content on the properties of two series of bioactive glasses in the quaternary system SiO₂-Na₂O-CaO-P₂O₅ was studied. The first series (I) was a simple substitution of P₂O₅ for SiO₂ keeping the Na₂O:CaO ratio fixed (1:0.87). The second series (II) was designed to ensure charge neutrality in the orthophosphate (), therefore as P₂O₅ was added the Na₂O and CaO content was varied to provide sufficient Na⁺ and Ca²⁺ cations to charge balance the orthophosphate present. Network connectivity’s of the glasses were calculated, and densities and thermal expansion coefficients predicted using the Appen and Doweidar models, respectively. Theoretical densities were measured using the Archimedes principle. Characteristic temperatures, namely the glass transition temperature, T_g, and crystallization temperatures, T_x, were obtained using differential analysis (DTA). Two crystallization exotherms were observed for both glass series (T_xi and T_xii). Both T_g and T_x decreased with P₂O₅ addition for both series. The working range of the glasses, T_x-T_g was shown to increase to a maximum at around 4 mol% P₂O₅ then decrease at higher P₂O₅ contents for both series. Thermal expansion coefficients were measured using dilatometry increasing with P₂O₅ addition and showed good agreement with the Appen values. Dilatometric softening points, T_s, were also measured, which increased with P₂O₅ addition. X-ray diffraction (XRD) was performed on the glasses to confirm their amorphous nature. The glass containing 9.25 mol% P₂O₅ from series I exhibited well-defined peaks on the XRD trace, indicating the presence of a crystalline phase.     

Non-isothermal crystallization kinetics of ZnO-BaO-B2O3-SiO2 glass

Glass of composition 40SiO₂-30BaO-20ZnO-10B₂O₃ (mol%) was made by conventional melting and casting process. Crystallization kinetics of above glass has been investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The procedure is applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. The crystallization results are analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism is characterized. Dilatometric measurement of this glass was also done and data obtained was used to calculate the viscosity of the formed glass. Development of crystalline phases on thermal treatments of the glass at various temperatures has been analyzed by X-ray diffraction. Microstructure of the crystalline phases was investigated by scanning electron microscopy (SEM) and the development of various structural features with variation in heat treatment cycle was observed. The nucleation and growth of these phases in the matrix of glass has been described and discussed.     

Crystallization processes of Li2O-Ga2O3-SiO2-NiO system glasses

Crystallization processes of Li₂O-Ga₂O₃-SiO₂-NiO system glasses have been studied by X-ray diffraction, differential calorimetry and optical absorption. Transparent glass-ceramic containing LiGa₅O₈:Ni²⁺ as the sole crystalline phase has been obtained from glass with the composition of 13Li₂O-23Ga₂O₃-64SiO₂-0.1NiO (in mol%) by the heat treatment in the temperature range from 923 to 953 K. It was revealed that the specific surface area of samples enhances crystallization of LiGaSi₂O₆ but obstructed that of LiGa₅O₈. LiGa₅O₈ grew to nano-sized crystallites dispersed in the glass matrices and did not affect the transparency seriously. In contrast, LiGaSi₂O₆ grew to crystallites with diameters more than 100 nm on the surface and made the glasses opaque. Optical absorption measurements revealed that doped Ni²⁺ occupied five-folded trigonal bipyramidal sites in the as-quenched glass matrices but six-folded octahedral sites of precipitated LiGa₅O₈ in the glass-ceramics. It was confirmed that transparent glass-ceramic containing Ni²⁺:LiGa₅O₈ was effectively obtained by the heat treatment at a temperature of 953 K for 10 h.     

Electron spin resonance and magnetic studies on CaO-SiO2-P2O5-Na2O-Fe2O3 glasses

Room temperature electron spin resonance (ESR) spectra and temperature dependent magnetic susceptibility measurements have been performed to investigate the effect of iron ions in 41CaO · (52 − x)SiO₂ · 4P₂O₅ · xFe₂O₃ · 3Na₂O (2 ? x ? 10 mol%) glasses. The ESR spectra of the glass exhibited the absorptions centered at g ≈ 2.1 and g ≈ 4.3. The variation of the intensity and linewidth of these absorption lines with composition has been interpreted in terms of variation in the concentration of the Fe²⁺ and Fe³⁺ in the glass and the interaction between the iron ions. The magnetic susceptibility data were used to obtain information on the relative concentration and interaction between the iron ions in the glass.     

Solubility of glasses in the system P2O5-CaO-MgO-Na2O-TiO2: Experimental and modeling using artificial neural networks

Phosphate glasses in the system P₂O₅-CaO-MgO-Na₂O-TiO₂ for use as degradable implant materials were produced. In order to classify their solubility behavior, dissolution experiments were performed in deionized water for 60 min at 98 °C. Resulting solutions were analyzed using ICP-OES. In addition, pH measurements were carried out in physiological NaCl solution. With increasing phosphorus oxide content, the glasses showed a higher solubility and gave lower pH values in aqueous solution. This was caused by changes in the glass structure, as long phosphate chains are more susceptible to hydration than smaller phosphate groups. These changes in glass structure were followed by ³¹P MAS-NMR experiments. Increasing sodium oxide concentrations in exchange for calcium or magnesium oxide also increased the glass solubility by disrupting ionic cross links between chains. By contrast, addition of titania made the glasses more stable towards dissolution by cross linking smaller phosphate groups. The aim of this study was to find a relationship between glass composition and solubility behavior. As classical linear methods of data analysis were unsuitable due to the complexity of the relationship, preliminary artificial neural networks analyses were performed and were found to be an interesting tool for modeling the solubility behavior of phosphate glasses.     

Properties characterization of the Cu68.5Ni12P19.5 alloy at elevated temperatures

The Cu_68.5Ni₁₂P_19.5 alloy was cast into the ribbons using melt spinning (23 m/s). The amorphous ribbon in the as-cast state was investigated by differential thermal analysis (DTA), dynamic mechanical analysis (DMA), resistivity measurements and X-ray diffraction ‘in situ’ at different temperatures. The work presents attempts to find correlation between the changes of the mechanical properties presented by DMA cycles and during the other tests. The measurements of the relative resistivity R/R₀ versus temperature for repeated heating and cooling cycles to different temperatures show changes of the temperature coefficient of resistivity (TCR) indicating reversible and irreversible transformations in the studied alloy.     

Remark on the optical gap in ZnO-Bi2O3-TeO2 glasses

Four ZnO-Bi₂O₃-TeO₂ glasses were prepared from high purity (4N5) oxides. From measurements of the optical transmission on very thin bulk samples the optical gap was determined at around 3.55 eV for the glasses studied. The temperature dependence of the optical gap was also determined from the room temperature close up to 500 K. Preliminary Raman scattering measurements indicate that with a decrease in TeO₂ content, TeO₄ trigonal bipyramid transformation proceeds into TeO₃ trigonal pyramids.     

Orthophosphate nanostructures in SiO2-P2O5-CaO-Na2O-MgO bioactive glasses

Vibrational spectroscopy, ²⁹Si and ³¹P magic-angle spinning nuclear magnetic resonance spectroscopy and high resolution transmission electron microscopy were used to investigate structural aspects of SiO₂-P₂O₅-CaO-Na₂O-MgO glasses. The experimental results show that for the two compositions, 25.3SiO₂-10.9P₂O₅-32.6CaO-31.2MgO and 33.6SiO₂-6.40P₂O₅-19.0CaO-41.0MgO, phosphorous is present in a nano-crystalline form with interplanar distances in the 0.21-0.26 nm range. The two glasses develop a surface CaP-rich layer and the presence of any intermediate silica-rich layer was not detected. It was suggested that the phosphate nano-regions may play a key role in the initial stages of the bioactive process, acting as nucleation sites for the calcium phosphate-rich layer.     

Optical properties of and concentration quenching in Bi2O3-B2O3-Ga2O3 glasses

Er₂O₃-doped Bi₂O₃-B₂O₃-Ga₂O₃ glasses were prepared by the conventional melt-quenching method, and the Er³⁺:⁴I_13/2 → ⁴I_15/2 fluorescence properties are studied for different Er³⁺ concentrations. when the Er₂O₃ concentration increases from 0.03 to 3.0 mol%, the measured lifetime of Er³⁺:⁴I_13/2 level decrease from 2.24 to 0.9 m s, and from 0.25 to 0.20 m s for the Er³⁺:⁴I_11/2 level. The fast energy migration among Er³⁺ ions cause the reduction of lifetime of the ⁴I_13/2 level, whereas the change in the ⁴I_11/2 level is mainly due to a cooperative upconversion process (⁴I_11/2, ⁴I_11/2) → (⁴F_7/2, ⁴I_15/2). Based on the dipole-dipole interaction theory, the interaction parameter, C_Er,Er, for the migration rate of Er³⁺:⁴I_13/2 ↔ ⁴I_13/2 was calculated to be 32 × 10⁻⁴⁰ cm⁶ s⁻¹.     

Structure and properties of Ni60(Nb100−xTax)34Sn6 bulk metallic glass alloys

Refractory bulk metallic glasses and bulk metallic glass composites are formed in quaternary Ni-Nb-Ta-Sn alloy system. Alloys of composition Ni₆₀(Nb_100−xTa_x)₃₄Sn₆ (x = 20, 40, 60, 80) alloys were prepared by injection-casting the molten alloys into copper molds. Glassy alloys are formed in the thickness of half mm strips. With thicker strips (e.g., 1 mm), Nb₂O₅ and Ni₃Sn phases and the amorphous phase form an in situ composite. Glass transition temperatures, crystallization temperatures, and ΔT_x, defined as T_x1 − T_g (T_x1: first crystallization temperature, T_g: glass transition temperature) of the alloys increase dramatically with increasing Ta contents. These refractory bulk amorphous alloys exhibit high Young’s modulus (155-170 GPa), shear modulus (56-63 GPa), and estimated yield strength (3-3.6 GPa).     

A study of nonlinear optical properties in Bi2O3-WO3-TeO2 glasses

A series of bismuth tungsten tellurite glasses were prepared and their densities, linear refractive indices and transmission spectra were measured. The optical bandgaps E_opt and Urbach energies E_e of glasses were obtained from ultraviolet absorption edges. Both the optical gap (E_opt) and the band tail (E_e) are behaving oppositely. As the value of E_opt decreases with increasing WO₃ content, the degree of disorder increases which causes more defects or localized states resulting in deep localized in the bandgap with the tailing increased. Z-scan technique was carried out to investigate the third-order nonlinear optical properties of Bi₂O₃-WO₃-TeO₂ glasses. The third-order optical nonlinearity increases with decreasing the optical bandgap E_opt, since a increase of WO₃ content can provide the non-bridging oxygen ion content.     

Sulfur behavior in silicate glasses and melts: Implications for sulfate incorporation in nuclear waste glasses as a function of alkali cation and V2O5 content

The presence of sulfur in radioactive waste to be incorporated in borosilicate glasses entails difficulties mainly due to the relatively low solubility of sulfates in the vitreous phase. In this work a study is presented on the effects of the ratio R = [Na₂O]/[B₂O₃], the type of sulfate added and the addition of V₂O₅ on the incorporation of sulfates in borosilicate glasses. Glass samples were prepared at the laboratory scale (up to 50-100 g) by melting oxide and sulfate powders under air in Pt/Au crucibles. XRF and ICP/AES chemical analysis, SEM/EDS, microprobe WDS and Raman spectroscopy were employed to characterize the fabricated samples. The main experimental results confirm that the incorporation of sulfates in borosilicate glasses is favored by the network depolymerization, which evolves with the ratio R. The addition of V₂O₅ seems to accelerate the kinetics of sulfur incorporation in the glass and, probably, increase the sulfate solubility by modifying the borate network and fostering the formation of voids of shape and size compatible with the sulfur coordination polyhedron in the glassy network. The kinetics of X₂SO₄ incorporation in the glass seems to be slower when X = Cs.     

Development and characterizations of BaO-CaO-Al2O3-SiO2 glass-ceramic sealants for intermediate temperature solid oxide fuel cell application

Several compositions based on BaO-CaO-Al₂O₃-SiO₂ (BCAS) glass system have been studied in this investigation to see their applicability as sealant for solid oxide fuel cell (SOFC). The glasses as well as the corresponding glass-ceramics have been systematically characterized by differential thermal analysis, dilatometry, X-ray diffractometry, electron microscopy and impedance analysis to examine their suitability as sealant. While the glass transition temperature (T_g) determined from DTA are within 600-665 °C, the coefficient of thermal expansion (CTE) can be tailored between 9.5 and 13.0 × 10⁻⁶ K⁻¹. These glasses are found to be well adhered with metallic interconnects, such as commercial ferritic steel (Crofer22APU), at an optimum sealing temperature of 850 °C. The shrinkage behavior of the developed glasses in their pellet form has also been investigated. The resistivities of the glass-ceramics, as obtained from impedance analysis, are found to be within 10⁴-10⁶ Ω cm at 800 °C. Under sandwiched condition between two metals, some of the developed compositions are found to maintain this high resistivity even after 100 h of operation. One of the glass compositions has shown a low leak-rate of the order of ∼10⁻⁷ Pa m² s⁻¹.     

Effect of the annealing process on the microstructure of La2Zr2O7 thin layers epitaxially grown on LaAlO3 by metalorganic decomposition

La₂Zr₂O₇ (LZO) films have been grown by metalorganic decomposition (MOD) to be used as buffer layers for coated conductors. A characteristic feature of LZO thin films deposited by MOD is the formation of nanovoids in an almost single crystal structure of LZO pyrochlore phase. Annealing parameters (heating ramp, temperature, pressure, etc.) were varied to establish their influence on the microstructure of the LZO layers. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for sample characterization. The epitaxial pyrochlore phase was obtained for annealing temperatures higher than 850 °C whatever the other annealing conditions. However, the film microstructure, in particular, nanovoids shape and size, is strongly dependent on heating ramp and pressure during annealing. When using low heating ramp, percolation of voids creates diffusion channels for oxygen which are detrimental for the substrate protection during coated conductor fabrication. From this point of view high heating rates are more adapted to the growth of LZO layers.