Transport of potassium ions in niobium phosphate glasses

The influence of Nb₂O₅ on the structure and ionic conductivity of potassium phosphate glasses was investigated in glasses with composition xNb₂O₅–(100-x)[0.45K₂O–0.55P₂O₅], x = 10–47 mol%. The Raman spectra of glasses reveal a transition from predominantly orthophosphate to predominantly niobate glass network with increasing Nb₂O₅ content. In the glass structure, niobium forms NbO₆ octahedra which are interlinked with phosphate units for the glass containing 10 mol% Nb₂O₅, but for higher Nb₂O₅ content they become mutually interconnected via Nb-O-Nb bonds. The transport of potassium ions was found to be strongly dependent on the structural characteristics of the glass network. While the mixed niobate-phosphate glass network hinders the diffusion of potassium ions by providing traps that immobilize them and/or by blocking the conduction pathways, predominantly niobate glass network exhibits a rather facilitating effect which is evidenced in the trend of DC conductivity as well as in the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions.     

High niobium oxide content in germanate glasses: Thermal,structural, and optical properties

Niobium alkali germanate glasses were synthesized by the melt‐quenching technique. The ternary system (90‐x)GeO₂–xNb₂O₅–10K₂O forms homogeneous glasses with x ranging from 0 to 20 mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb₂O₅ content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO₆ groups insertion close to GeO₄ units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide‐rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb₂O₅. Absorption spectra revealed high transmission range between 400 nm to 6.2 μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide‐rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass‐ceramics.     

Effects of Nb2O5 and Gd2O3 doping on boron volatility and activity between glass seals and lanthanum-containing cathode

In planar Solid Oxide Fuel Cells (SOFCs), the boron species volatilize from glass seals, and react with lanthanum-containing cathodes (i.e., La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ, LSCF) to form LaBO₃ under cathodic polarization, which decomposes the perovskite structure and consequently decreases the electrochemical activity of cathode. In this study, Nb₂O₅ and Gd₂O₃ are added to an aluminoborosilicate glass to reduce the boron volatility from glass and the reaction between sealing glass and LSCF cathode. Both Nb₂O₅ and Gd₂O₃ doping increases the network connectivity, but Nb₂O₅ doping enhances the [BO₃] → [BO₄] transition and reduces the boron volatility from glass seals, thus effectively suppressing the deposition and poisoning of boron contaminants on the LSCF cathode. However, an obvious degradation of the electrocatalytic activity of LSCF occurs in the presence of Gd₂O₃-doped glass. The relationship between glass structure and glass/cathode interaction has been established to provide useful information for designing stable sealing materials for SOFC applications.     

Understanding the structure,thermal, and optical properties in Al2O3-incorporated La2O3-TiO2-Nb2O5 glasses

Glasses in the 30La₂O₃-40TiO₂-30Nb₂O₅ system are known to have excellent optical properties such as refractive indices over 2.25 and wide transmittance within the visible to mid-infrared (MIR) region. However, titanoniobate glasses also tend to crystallize easily, significantly limiting their applications in optical glasses due to processing challenges. Therefore, the 30La₂O₃-40TiO₂-(30−x) Nb₂O₅-xAl₂O₃ (LTNA) glass system was successfully synthesized using a aerodynamic containerless technique, which improves glass thermal stability and expands the glass-forming region. The effects of Al₂O₃ on the structure, thermal, and optical properties of base composition glasses were investigated by XRD, DSC, NMR, Raman spectroscopy, and optical measurements. DSC results indicated that as the content of Al₂O₃ increased, the thermal stability of the glasses and glass-forming ability increased, as the 30La₂O₃-40TiO₂-25Nb₂O₅-5Al₂O₃ (Nb-Al-5) glass obtained the highest ΔT value (103.5°C). Structural analysis indicates that the proportion of [AlO₄] units increases gradually and participates in the glass network structure to increase connectivity, promoting more oxygen to become bridging oxygen and form [AlO₄] tetrahedral linkages to [TiO₅] and [NbO₆] groups. The refractive index values of amorphous glasses remained above 2.1 upon Al₂O₃ substitution, and a transmittance exceeding 65% in the visible and mid-infrared range. The crystallization activation energies of 30La₂O₃-40TiO₂-30Nb₂O₅ (Nb-Al-0) and Nb-Al-5 glasses were calculated to be 611.7 and 561.4 kJ/mol, and the Avrami parameters are 5.28 and 4.96, respectively. These results are useful to design new optical glass with good thermal stability, high refractive index and low wavelength dispersion for optical applications such as lenses, endoscopes, mini size lasers, and optical couplers.     

Insulating characteristics of zinc niobium borate glass‐ceramics

Zinc borate glasses with different concentrations of Nb₂O₅ were prepared and later were heat treated for prolonged times. Prepared samples were characterized by XRD, SEM, DSC, IR and optical transmission spectroscopy techniques. Later, dielectric properties viz., dielectric constant, loss tangent, electric modulii, electrical impedance and a.c. conductivity over wide ranges of frequency and temperature, were investigated as a function of Nb₂O₅ concentration. Finally, the dielectric breakdown strength was measured in air medium at ambient temperature. The results of characterization techniques viz., XRD, SEM and DSC indicated that multiple crystal grains (with sizes varying from 0.1 to 1 μm) are dispersed in the residual glass phase. The concentration of crystal grains found to increase with increase in Nb₂O₅ content. The XRD studies have further revealed that the bulk samples are composed of columbite ZnNb₂O₆ crystal phases. Using generalized gradient approximation (GGA) quantitative information on these crystal phases viz., the lattice parameters, optical band gap and band structure were evaluated. The analysis of results of IR spectral studies have indicated that there is an increasing degree of polymerization of glass network with increase in Nb₂O₅ content due to the increased connectivity between various structural groups in the glass network. The optical absorption spectra indicated an increase in optical transmittance of the bulk samples with increase in Nb₂O₅ content. The dielectric parameters are observed to decrease, whereas the dielectric breakdown strength is observed to increase to a large extent due to the crystallization of the glass with the Nb₂O₅. The increase is attributed to the formation of ZnNb₂O₆ crystalline phases that contain intertwined ZnO₆ and NbO₆ structural units. As a whole, zinc borate glasses exhibited a significant increase in the electrical insulating strength due to the crystallization with Nb₂O₅ as the crystallizing agent. Further, the value of dielectric constant is also found to be the optimal with no dispersion with frequency up to 450 K. Overall, the studied glass‐ceramics meet the necessary physical conditions to be used as insulating layers in the display panels and hence may be considered for such applications.     

Integration Between Optical and Structural Behavior of Heavy Metal Oxide Glasses Doped with Multiple Glass Formers

Heavy metal oxide glasses (composition 60 PbO, 20 Bi₂O₃ mol%) and containing 20 mol% conventional glass formers SiO₂, B₂O₃, and P₂O₅ were prepared. Combined optical and Fourier transform infrared absorption spectra were measured for the prepared glasses to justify the role of glass formers in the optical spectra together with the network structural groups in such glasses. Also, the density and molar volume values were calculated to obtain some insight on the compactness and arrangement in the network. Optical measurements have been used to determine the optical band gap (E_g), Urbach energy (ΔE) and the refractive index (n). Optical spectra of all the samples reveal strong UV absorption which is related to the presence of unavoidable trace iron impurities (Fe ³⁺ ions) contaminated within the raw materials which were used for the preparation of the studied glasses. Additional near visible bands are observed in all prepared glasses due to characteristic absorption of Pb ²⁺ and Bi ³⁺ ions. Furthermore, The variations of the luminescence intensity, values of the optical band gap, band tail, and refractive index can be understood and related in terms of the structural changes that take place in the glass samples. The infrared absorption spectra of the prepared glasses show characteristic absorption bands related to the borate or silicate or phosphate network (BO₃, BO₄, SiO₄, PO₄ groups) together with vibrational modes due to Bi-O and Pb-O groups.     

Thermal Stability,Optical Transmittance,and Refractive Index Dispersion of La2O3–Nb2O5–Al2O3 Glasses

La₂O₃–Nb₂O₅–Al₂O₃ high‐refractive‐index glasses were fabricated by containerless processing, and the glass‐forming region was determined. The thermal stability, density, optical transmittance, and the refractive index dispersion of these glasses were investigated. All the glasses were colorless and transparent in the visible to near infrared (NIR) region and had high refractive index with low wavelength dispersion. Some of these glasses were found to have significantly high glass‐forming ability. These results indicate that the ternary glasses are suitable for optical applications in the visible to NIR region. The effects of the substitution of Al₂O₃ for Nb₂O₅ on optical properties were discussed on the basis of the Drude–Voigt equation. It was suggested that the substitution of Al₂O₃ for Nb₂O₅ increased the molecular density and suppressed a decrease in the refractive index, even when both the average oscillator strength and inherent absorption wavelength decreased in La₂O₃–Nb₂O₅–Al₂O₃ glasses. These results are helpful for designing new optical glasses controlled to have a higher refractive index and lower wavelength dispersion.     

Effect of Al2O3 content on BaO–Al2O3–B2O3–SiO2 glass sealant for solid oxide fuel cell

The glass structure, wetting behavior and crystallization of BaO–Al₂O₃–B₂O₃–SiO₂ system glass containing 2–10 mol% Al₂O₃ were investigated. The introduction of Al₂O₃ caused the conversion of [BO₃] units and [BO₄] units to each other and it played as glass network former when the content was up to 10 mol%, accompanied by [BO₄] → [BO₃]. The stability of the glass improved first and then decreased as Al₂O₃ increased from 2 to 10 mol%, the glass with 5 mol% Al₂O₃ being the most stable one. The wetting behavior of the glasses indicates that excess Al₂O₃ leads to high sealing temperature. The glass containing 5 mol% Al₂O₃ characterized by a lower sealing temperature is suitable for SOFC sealing. Al₂O₃ improves the crystallization temperature of the glass. The crystal phases in the reheated glasses are mainly composed of Ba₂Si₃O₈, BaSiO₃, BaB₂O₄ and BaAl₂Si₂O₈. Al₂O₃ helps the crystallization of BaSiO₃ and BaAl₂Si₂O₈.     

P2O5-BaO-Nb2O5三元系统玻璃的形成及性能的研究

研究P     

Thermal and optical properties of La2O3–Ga2O3– (Nb2O5 or Ta2O5) ternary glasses

La₂O₃–Ga₂O₃–M₂O₅ (M = Nb or Ta) ternary glasses were fabricated using an aerodynamic levitation technique, and their glass‐forming regions and thermal and optical properties were investigated. Incorporation of adequate amounts of Nb₂O₅ and Ta₂O₅ drastically improved the thermal stabilities of the glasses against crystallization. Optical transmittance measurements revealed that all the glasses were transparent over a wide wavelength range from the ultraviolet to the mid‐infrared. The refractive indices of the glasses increased and the Abbe number decreased upon substituting Ga₂O₃ with Nb₂O₅, and the decrease in the Abbe number was significantly suppressed when Ta₂O₅ was incorporated into the glass. As a result, excellent compatibility between high refractive index and lower wavelength dispersion was realized in La₂O₃–Ga₂O₃–Ta₂O₅ glasses. Analysis based on the single‐oscillator Drude–Voigt model provided more systematical information and revealed that this compatibility was due to an increase in the electron density of the glass.     

The effect of boron substitution for aluminium on the microstructure of calcium fluoro-aluminosilicate glasses and glass-ceramics

Calcium fluoro-aluminosilicate (4.5SiO₂-3Al₂O₃-1.5P₂O₅-3CaO-2CaF₂) glasses have significant applications in the medical and dental fields. However, due to the biological hazard of aluminium in the human body, this study focused on the influence of boron substitution for aluminium on the structure and properties of a series of substituted glasses and their correlated glass-ceramics. The results indicated that by increasing the amount of boron, the density of glasses and their glass-ceramics both decreased, whereas the number of bridging oxygens in the glasses increased. The glass transition temperature and the crystallization temperature remained almost unchanged for the glasses with a boron substitution of less than 25 mol%. Boron formed oxygen bridges in all glasses in the form of BO₃ triangles and BO₄ tetrahedra. Reducing the Al content in glasses, had an effect on the morphology and orientation of the fluorapatite crystal phase formed.     

Hydrodechlorination of 1,2,4-trichlorobenzene over niobia supported nickel catalysts

A series of nickel (2–15 wt%) catalysts supported on niobia were prepared. Their catalytic efficiency in the vapour phase hydrodechlorination of 1,2,4-trichlorobenzene was studied. The catalyst samples were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR) and hydrogen chemisorption methods. Hydrogen chemisorption studies suggest that the hydrogen spillover culminates at 6 wt% of Ni/Nb₂O₅. The partial hydrodechlorination ability of 6 wt% Ni/Nb₂O₅ was also found to be the highest. Niobia supported nickel catalysts were found to be highly active for the partial hydrodechlorination of 1,2,4-trichlorobenzene. It was also found that the catalytic properties are related to dispersion of nickel on niobium oxide.     

Influences of La and Er on structure and properties of Bi2O3–B2O3 glass

Bi₂O₃·2B₂O₃ glasses doped with La₂O₃ and Er₂O₃ were prepared by the melting-quenching method with AR-grade oxides. IR analysis was used to investigate the glass network structure. The characteristic temperatures including the glass transition temperature (T_g), crystallization temperature (T_p), and melting temperature (T_m) were estimated by DSC. The coefficient of thermal expansion (α), mass density (D), and Vickers hardness (H_v) were also measured. The results show that the basic network structure of Bi₂O₃·2B₂O₃ glasses doped with rare-earth oxides consists of chains composed of [BO₃], [BO₄], and [BiO₆] units. La₂O₃ and Er₂O₃ act as network modifiers. As the doping concentrations of the rare-earth oxides were increased, T_g increased and α decreased, indicating that a more rigid glass was obtained. Er₂O₃ reduces the melting temperature and prevents glass crystallization. La₂O₃ contributes to the improvement of the microhardness of Bi₂O₃·2B₂O₃ glass.     

Phase Separation and Crystallization in Glasses of the Na2O–K2O–Nb2O5–SiO2 System

The structure of initial glasses in the Na₂O–K₂O–Nb₂O₅–SiO₂ system with an Nb₂O₅ content ranging from 5 to 39 mol % and their structural transformations in the course of isothermal treatments at different temperatures are investigated using small-angle X-ray scattering (SAXS) and X-ray powder diffraction. It is demonstrated that, in glasses containing 15 mol % Nb₂O₅ and more, the metastable phase separation is the primary process responsible for the formation of a microinhomogeneous structure. With further heat treatment of these glasses, NaNbO₃ crystals precipitate in regions with a high Nb₂O₅ content. In this case, each region has a heterogeneous structure and consists of NaNbO₃ microcrystals surrounded by layers of the high-silica matrix. These layers hinder transfer processes and, consequently, recrystallization, which ensures the stability of the heterogeneous structure and, correspondingly, constant sizes of microcrystals at temperatures up to 750–800°C. The intensity of light scattering is determined primarily by the sizes of regions formed upon phase separation. A decrease in their size with an increase in the niobium oxide content leads to a decrease in the light scattering loss and an increase in the transparency of heat-treated samples. The interference effects associated with the heterogeneous structure of high-niobate phase regions also favor an increase in the transparency of the prepared materials.     

The impact of Nb2O5 on in-vitro bioactivity and antibacterial activity of CaF2–CaO–B2O3–P2O5–SrO glass system

This work consists of in vitro bioactivity (in SBF) and antibacterial studies (against S. aureus and E. coli bacteria) of Nb₂O₅ doped bioactive glasses. X-ray diffraction and scanning electron microscopy investigations indicated deposition of Nb-HAp (hydroxyapatite) crystalline layer on the samples after exposing to SBF. The spectroscopy investigations also indicated the deposition of HAp layer on these samples. The magnitude of HAp deposited on the glasses found to be relying on concentration of Nb₂O₅ dopant; this conclusion was drawn by determining weight loss of the glasses due to exposure to SBF and also by assessing the variation of pH of the remnant fluid as functions of Nb₂O₅content. The studies further indicated the maximal content of hydroxyapatite was deposited on the surface the glasses doped with 4.0 mol% of Nb₂O₅. The antibacterial studies (against E. coli and S. aureus bacteria) of these glasses indicated the maximal killing effect of bacteria of the samples admixed with 4.0 mol% of Nb₂O₅. This result is attributed to the occupancy of maximal fraction of Nb ions in NbO₆ structural units (confirmed by IR and Raman spectroscopic results) in this sample that paved the way for easy disintegration of the glass and to act on the bacteria. Overall, the results of bioactivity studies of Nb₂O₅ doped bioglasses indicated that the Nb₂O₅ not only enhanced bioactivity potential but also exhibited antimicrobial activity.     

Optical properties,thermal stability,and forming region of high refractive index La2O3–TiO2–Nb2O5 glasses

The high refractive index La₂O₃–TiO₂–Nb₂O₅ glasses were prepared by containerless processing, and the glass‐forming region was determined. The refractive index showed the range from 2.20 to 2.32, and the values were much higher than those of most optical glasses. The completely miscible 30LaO_3/2–(70?x)TiO₂–xNbO_5/2 (0 ≤ x ≤70) system was fabricated to study the compositional dependence of refractive index and optical transmittance. The crucial determinants of the refractive index of oxide glasses, oxygen molar volume, and electronic polarizability of oxygen ions were calculated. The principle of additivity of glass properties was suitable for the calculation of refractive index between glass and compositional oxides. All the glasses were colorless and transparent in the visible to 6.5 μm middle infrared (MIR) region. These results are useful for designing new optical glasses with high refractive index and low wavelength dispersion in wide optical window.     

A new catalyst material based on niobia/iron oxide composite on the oxidation of organic contaminants in water via heterogeneous Fenton mechanisms

The present work describes the preparation of novel materials based on niobia (Nb₂O₅)/iron oxides and their use as catalyst on oxidizing reactions of organic compounds in aqueous medium with hydrogen peroxide. These new composites were prepared by mixing natural niobia and iron oxides and were characterized with powder X-ray diffraction (XRD), chemical analyses, scanning electron microscopy (SEM), and ⁵⁷Fe Mössbauer spectroscopy. Results showed that the main iron oxides so formed were goethite (αFeOOH) and maghemite (γFe₂O₃) with small particle sizes. The decomposition study was realized with a basic dye as a model molecule: the methylene blue. The analysis of the products, with electrospray ionization mass spectrometry (ESI-MS), showed that the methylene blue was successively oxidized (hydrolyzed) through different intermediate species. These results strongly suggest that highly reactive hydroxyl radicals generated from the H₂O₂ on the surface of the 1:1 niobia:iron oxide composite act as an efficient heterogeneous Fenton catalyst     

Synthesis,physical, optical,structural and radiation shielding characterization of borate glasses: A focus on the role of SrO/Al2O3 substitution

In a bid to expand the amount of information available on glass systems and their potential applications for radiation shielding design, glass samples with the compositions (30-x)SrO-xAl₂O₃–68B₂O₃–2V₂O₅(x = 5, 7.5, 10, 12.5&15 mol %) coded as SABV0 - 4 were prepared by the melt-quenching technique and analyzed for their optical, structural, physical, and radiation shielding features. The glassy (amorphous) nature of the SABV glass samples was affirmed by broad peaks of X-ray diffraction spectra. Calculated values of density and molar volume shown opposite behavior and the variation of these values were discussed as structural modifications in the glass matrix. From recorded optical absorption spectra optical band gap energy (Eg)-indirect transition, Urbach energy and optical basicity were estimated. FTIR spectra were recorded for all the samples in the range 400 cm^?1 to 4000 cm^?1. The FTIR absorbance spectra unveiled the SABV network structure mainly incorporating of BO₃ and BO₄ units. Raman spectroscopy is achieved to detect the structural changes and at higher wavenumber, B–O stretching modes in [BO₃] observed with one or two NBO's. The results of ESR spectra of glasses have indicated the highly covalent environment of vanadium ions. Analysis of the photon shielding parameters of the glasses which were obtained primarily from FLUKA Monte Carlo simulations and XCOM computations revealed photon energy and glass chemical composition dependence. The mass attenuation coefficient and effective atomic number ranged from 0.2668 to 0.3385 cm²g^-1 and 12.98–15.93 accordingly as the weight fraction of Sr increased from 16.06 to 26.72% in the glasses. Generally, photon shielding ability of the SABV glasses follows the trend: SABV0 > SABV1 > SABV2 > SABV3 > SABV4. The thermal neutron total cross section follows the same trend with values fluctuating between 71.9553 and 80.6268 cm^?1. However, SABV1 showed superior fast neutron moderating capacity among the glasses. The present SABV glasses showed outstanding photon shielding ability compared to common shields. The prepared glasses are thus suitable candidates for radiation protection applications.     

Influence of the composition of high-lead phosphate glasses on the location of the UV transmission edge and technological quality

This paper reports on the results of an investigation into the influence of the purity of the initial materials used for preparing vitreous lead metaphosphate, the acidity of the phosphate matrix, and the contents of additives of Group I–III and V elements and the second glass-former on the location of the UV transmission edge of simple binary and ternary lead phosphate glasses. It is shown that, even for a binary glass of the composition (mol %) 50PbO · 50P₂O₅, the location of the UV transmission edge can be shifted by ～50 nm on the wavelength scale depending on the purity of the initial reactants. The shift of the UV transmission edge toward the UV spectral range for ternary glasses containing no variable-valence elements other than lead is considerably larger than that for the high-lead phosphate glass of the previously proposed composition involving antimony, niobium, and cerium oxides. It is established that the addition of niobium oxide Nb₂O₅ to lead phosphate glasses brings about a red shift of the UV transmission edge and a change in the crystallization ability of the glasses. Niobium oxide at a content up to 1.5 mol % increases the crystallization ability of the glass, whereas a change in the niobium oxide content from 1.5 to 3.1 mol % results in a decrease in the crystallization ability. It is demonstrated that the crystallization ability of high-lead phosphate glasses increases at a boron oxide content higher than 5 mol %.     

Bismuth and lead oxides codoped boron phosphate glasses for Faraday rotators

New magneto-optical vitreous materials were obtained by melting-quenching technique comprising wet route raw materials preparation. The glass has the following composition in oxide mol. %: 10 Li₂O, 9 Al₂O₃, 5 ZnO, (35; 20; 50) B₂O₃, (35; 50; 20) P₂O₅, 3 Bi₂O₃, 3 PbO, phosphorus and boron oxide being the vitreous network formers. It was also prepared a similar reference glass composition but without Bi₂O₃ and PbO. Optical and structural characterization by ultraviolet-visible (UV–Vis), Fourier Transform Infrared (FTIR) and Raman Spectroscopy of the bulk glasses showed a transmission over 90%, metaphosphate structure of glass together with Q² boron oxide units and P–O?B bonds. The mechanical parameters, hardness (H), Young's modulus (E) and fracture toughness (K_IC) of boron phosphate glasses, evaluated by micro- and nanoindentation techniques, demonstrated mostly higher values in comparison with those for alumino-phosphate glasses due to mixed boro-phosphate network. Thermal behavior was investigated by Differential Scanning Calorimetry (DSC) putting in evidence the vitreous transition temperature which decreases with about 45 °C when Bi and Pb oxides were added and two crystallization effects. The diamagnetic character of a highly transparent Bi and Pb oxide co-doped boron phosphate glass was confirmed by ellipsometry, and the glass presented high magneto-optical properties at the top of the commercial bulk products.