Effects of Nb2O5 Replacement by Er2O3 on elastic and structural properties of 75TeO2-(10 − x)Nb2O5-15ZnO-(x)Er2O3 glass

Tellurite 75TeO₂-(10 − x)Nb₂O₅-15ZnO-(x)Er₂O₃; (x = 0.0-2.5 mol%) glass system with concurrent reduction of Nb₂O₅ and Er₂O₃ addition have been prepared by melt-quenching method. Elastic properties together with structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo-overlap technique at 5 MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at x = 0.5 mol% but remained constant between x = 1.0 mol% to x = 2.0 mol%, before increasing back with Er₂O₃ addition at x = 2.5 mol%. The initial drop in shear velocity and related elastic moduli observed at x = 0.5 mol% were suggested to be due to weakening of glass network rigidity as a result of increase in non-bridging oxygen (NBO) ions as a consequence of Nb₂O₅ reduction. The near constant values of shear velocity, elastic moduli, Debye temperature, hardness and Poisson's ratio between x = 0.5 mol% to x = 2.0 mol% were suggested to be due to competition between bridging oxygen (BO) and NBO ions in the glass network as Er₂O₃ gradually compensated for Nb₂O₅. Further addition of Er₂O₃ (x > 2.0 mol%) seems to further reduce NBO leading to improved rigidity of the glass network causing a large increase of ultrasonic velocity (v_L and v_S) and related elastic moduli at x = 2.5 mol%. FTIR analysis on NbO₆ octahedral, TeO₄ trigonal bipyramid (tbp) and TeO₃ trigonal pyramid (tp) absorption peaks confirmed the initial formation of NBO ions at x = 0.5 mol% followed by NBO/BO competition at x = 0.5-2.0 mol%. Appearance of ZnO₄ tetrahedra and increase in intensity of TeO₄ tbp absorption peaks at x = 2.0 mol% and x = 2.5 mol% indicate increase in formation of BO.     

Influence of CoO addition on phase separation and crystallization of glasses of the ZnO–Al2O3–SiO2–TiO2 system

The evolution of structure, phase composition and spectroscopic properties of CoO-doped (up to 5 mol%) titania-containing zinc aluminosilicate glasses with their heat-treatment has been studied using Raman scattering, small angle X-ray scattering, X-ray diffraction analysis and optical absorption spectra. Addition of cobalt oxide was observed to facilitate amorphous phase separation of the parent glass and gahnite, ZnAl₂O₄, crystallization. Cobalt oxide entered phases formed during low-temperature heat-treatments (720 °C), i.e., amorphous phase, enriched in ZnO, Al₂O₃ and TiO₂ and crystalline phase of gahnite. The absorption of these glass-ceramics was defined mainly by tetrahedral Co²⁺ ions located in gahnite nanocrystals. As the temperature was increased further, traces of anosovite solid solution appeared and then decomposed. Even after high-temperature heat-treatments, a certain portion of Co²⁺ ions remained in amorphous zinc aluminotitanate phase and in octahedral sites of inversed gahnite spinel. In glass-ceramics, the residual high silica amorphous phase contained a small quantity of [TiO₄] centers, which content was smaller in Co:ZAS samples as compared with non-doped glass-ceramics.     

Characterization of chemosynthetic Al2O3-2SiO2 geopolymers

Pure chemosynthetic Al₂O₃-2SiO₂ geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol-gel method. The molecular structure of the precursor powder and resulting geopolymers were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis. In addition, the mechanical and alkali-activated polymerization properties of these materials were also studied. NMR data revealed that the chemosynthetic powders began to contain 5-coordinated Al atoms when the calcination temperatures exceeded 200 °C. These calcined powders were capable of reacting with sodium silicate solutions at calcination temperatures exceeding 300 °C, which is, however, much lower than the temperature required to convert kaolin to Metakaolin.     

Study of the structural insertion of Al in the Al2O3-SiO2 and Nd2O3-Al2O3-SiO2 glass systems

Glasses in the Al₂O₃-SiO₂ and Nd₂O₃-Al₂O₃-SiO₂ systems were prepared by the sol-gel method. The gel-glass evolution was studied using near-infrared (NIR) and ultraviolet-visible (UV-VIS) spectrophotometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The results obtained indicate a relationship between the sample compositions, the treatment temperature and the Al coordination. In the samples of the Nd₂O₃-Al₂O₃-SiO₂ system the densification of the structure, when the treatment temperature increases, leads to the segregation of neodymium oxide particles.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

Sol-gel preparation and optical properties of SiO2-Ta2O5 glass

Tantalum-doped silica glass was fabricated by the sol-gel process in order to obtain a glass with a high refractive index for optical use. A crack-free, clear glass rod was successfully prepared from a low-density gel and used as the core material for fabricating optical fibers. Transmission loss in the fabricated fibers was high, in the range of 10³-10⁴ dB/km, which may be caused by coloration due to the multivalency of tantalum; however, the loss was reduced by nearly one order of magnitude by heat treatment at 800 °C, that is, to 75 dB/km at a wavelength of 0.8 μm.     

Linear optical properties of BaNaB9O15, BaLiB9O15 and SrLiB9O15 glasses

Transparent BaNaB₉O₁₅ (BNBO), BaLiB₉O₁₅ (BLBO) and SrLiB₉O₁₅ (SLBO) glasses were fabricated via the conventional melt-quenching technique. X-ray diffraction (XRD) and Differential thermal analysis (DTA) studies carried out on the as-quenched glasses confirmed their amorphous and glassy nature, respectively. The optical properties for these as-quenched glasses were investigated. The refractive index, optical band gap, Urbach energy and Fermi energy were determined. The average electronic polarizability calculated from the refractive index expression.     

Effect of Bi2O3 proportion on physical, structural and electrical properties of zinc bismuth phosphate glasses

The variation in physical, structural and electrical properties has been studied as a function of Bi₂O₃ content in 20ZnF₂-(10 + x) Bi₂O₃-(70-x) P₂O₅, 0 ≤ x ≤ 10 mol% glasses, which were prepared by melt quenching technique and characterized by differential thermal analysis (DTA). Colorless samples, which have no absorption peaks, are obtained for 10 and 12 mol% of Bi₂O₃ and the glasses are slowly becoming brownish from 15 to 20 mol% of Bi₂O₃ which exhibit two absorption peaks at ~ 370 nm, ~ 450 nm correspond to Bi° transitions ⁴S_3/2 → ²P_3/2 and ⁴S_3/2 → ²P_1/2 respectively. The decrease in ³P₁ → ¹S₀ transition of Bi³⁺ photo luminescence emission for 18 and 20 mol% of Bi₂O₃ and increase in optical absorption area shows the reduction of Bi³⁺ to Bi°. From FTIR studies it is observed that an addition of Bi₂O₃ decreases the P―O―P covalent bond by forming P―O―Bi bonds due to high polarizing nature of Bi³⁺ ions. Dielectric parameters like ε', tan δ and a.c. conductivity σ_ac are found to increase and activation energy for a.c. conduction is found to decrease with the increase in the concentration of Bi₂O₃. Density of defect energy states is found to increase for higher concentration of Bi₂O₃ and is discussed according to quantum mechanical tunneling (QMT) model.     

Spectroscopic properties of Er-doped xGeO2-(80 − x)TeO2-10ZnO-10BaO glasses

Erbium-doped glasses with composition xGeO₂-(80 − x)TeO₂-10ZnO-10BaO were prepared by melt-quenching technique. The phonon sideband spectra and the optical absorption band edges for the host matrix were confirmed by means of the spectral measurements. Standard Judd-Ofelt calculations have been completed to these glasses. The dependence of up-conversion and infrared emission under 980 nm excitation on the glass composition was studied. The quantum efficiencies for the ⁴I_13/2 → ⁴I_15/2 transition of trivalent erbium in the glasses were estimated.     

Vibrational spectral analysis of structural modifications of Cr2O3 containing oxyfluoroborate glasses

Infrared and Raman spectra of oxyfluoroborate glasses of the compositions 20CaF₂-20 ZnO-(60-x) B₂O₃-x Cr₂O₃ with 0 ≤ × ≤ 0.10 mol% (x = 0, 0.02, 0.04, 0.05, 0.06, 0.07, 0.08 and 0.1) have been analyzed in order to explain the role of Cr₂O₃ on the structure of these glasses. Density, molar volume, oxygen molar volume and oxygen packing density are determined to explain the packing of the atoms in the glasses. From these studies, the existence of different borate groups like di-, tri-, tetra-, penta-, ortho-, pyro- and metaborates in these glasses is established. With the increase in the concentration of Cr₂O₃ up to 0.06 mol%, conversion of BO₃ units into BO₄ units and above this mole fraction the reconversion of BO₄ units into BO₃ units is observed. The breaking and reforming of the boroxol ring is explained from the Raman spectral studies of these glasses.     

Sodium tracer diffusion in glasses of the type (CaO·Al2O3)x(2 SiO2)1−x

Tracer diffusion coefficients of the radioactive isotope Na-22 were measured in glasses of the type (CaO·Al₂O₃)_x(2 SiO₂)_1−x to study the diffusion of sodium as a function of glass composition, x, temperature and initial water content. The diffusion of Na-22 in glasses diffusion-annealed in dry air can always be well described by a single tracer diffusion coefficient, but sometimes not in samples annealed in common air. It was found that the sodium tracer diffusion coefficient decreases by about six orders of magnitude when the glass composition x changes from 0 to 0.75 at 800 °C. The temperature dependence of the diffusion of sodium seems to decrease as the silica content increases. Variations of the initial water content in some of the glasses investigated did not very significantly influence the rate of the tracer diffusion of sodium.     

Structural study of (As2S3)0.6(GeS2)0.4 glass

(As₂S₃)_0.6(GeS₂)_0.4 glass in non-irradiated and γ-irradiated states has been studied by using high-energy synchrotron X-ray diffraction, extended X-ray absorption fine structure spectroscopy, and positron annihilation lifetime spectroscopy. The experimental results are explained by the local changes around As and Ge atoms upon irradiation. These changes are suggested to involve chemical bonds distortion, formation of defective bonds with wrong coordination, rotation of structural units and appearance of additional free volume in the glass network.     

Study of optical and conducting properties of FeCl3 doped PVA polymers

In the present work, PVA and various concentrations of FeCl₃ doped PVA polymer were prepared and optical studies like IR and UV/Visible analysis were carried out on them in solution form also the cast films were examined for their conductance. The variation of optical band gap of PVA polymer with the addition of Fe³⁺ transition metal ion has been determined by the Tauc plot method. It is found that the optical band gap and the transmittance of the polymer solutions being decreased with the increase in the concentration of Fe³⁺ ion, and thus obeys Beer's Law. This is supported by conductivity obtained for these polymers and FT-IR spectra which shows the stretching of the various bonds of the polymer due to the addition of transition metal (Fe³⁺) ions.     

Bioactive glasses in the system CaO-B2O3-P2O5: Preparation, structural study and in vitro evaluation

Glasses in the system x B₂O₃(1 − x) [y CaO P₂O₅], (x = 0, 0.1, 0.2, 0.3, y = 2, 2.6, 3, 4, 5) have been prepared by fast quenching of high temperature melts. The presence of B₂O₃ affected the glass forming ability, allowing the preparation of calcium phosphate glasses with y ? 2.6. The structure of glasses was analyzed by μ-Raman and infrared spectroscopy. The analysis indicated that the glass network is dominated by highly charged species from phosphate tetrahedra with 3 (pyro) or 4 (ortho) NBOs, while the boron atoms are incorporated mainly in 3 coordinated sites in the form of B∅₃ or B∅₂O⁻ units. A small fraction of units was also evident from the spectra analysis of glasses with high CaO content. All calcium borophosphate glasses exhibited bioactivity after soaking in SBF solution within a few days. This was observed by μ-Raman and SEM microscopy, while XRD patterns clearly revealed growth of hydroxyapatite phase. The presence of boron in the glass network has a catalytic effect at favoring bioactivity of the otherwise bioinert calcium phosphate glasses.     

Thermally modulated differential scanning calorimetry of a glass of composition 45Na2O-40B2O3-10Al2O3-5In2O3

The kinetics of structural relaxation and of glass transition of the 45Na₂O-40B₂O₃-10Al₂O₃-5In₂O₃ glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems).     

Sodium tracer diffusion in glasses of the type (Na2O)0.2(B2O3)y(SiO2)0.8 − y

Sodium tracer diffusion coefficients, D^?_Na, have been measured in sodium borosilicate glasses of the type (Na₂O)_0.2(B₂O₃)_y(SiO₂)_0.8−y as a function of temperature and the composition parameter y. At constant temperature, the tracer diffusion coefficient of sodium decreases as y increases. The activation enthalpy derived from sodium tracer diffusion data for temperatures up to about 350 °C increases about linearly with increasing values of y from about 70 to 100 kJ/mol. The pre-exponential factor of the sodium tracer diffusion coefficient as a function of y varies by about one order of magnitude and has a minimum at near y = 0.3.     

A structural study of Y2O3---Al2O3---SiO2 glass employing partial RDFs obtained by anomalous scattering

A structural study of Y₂O₃---Al₂O₃---SiO₂ glass has been performed using the partial radial distribution function (RDF) obtained by anomalous scattering at the Y absorption edge. The partial RDF consists of contributions from atom pairs, such as Y---O, Y---M(Si, Al) and Y---Y, related to the local arrangements around the Y atoms, while those of all of the constituent atom-pairs are convoluted into the ordinary RDF. The M(Si, Al)---O, Y---O, M---M, Y---M, and Y---Y interatomic distances and the coordination numbers around the Al and Y atoms are obtained from the two RDFs. The local structures around the Al and Y atoms in the glass are discussed.     

Structural and transport properties of quaternary glass system: LiF-Li2O-SrO-Bi2O3

Bismuth based glasses containing LiF, Li₂O and SrO were investigated by different physical, spectroscopic and transport techniques. The results show that density of the glass system increases whereas glass transition temperature decreases with increase in LiF content. The decrease in glass transition temperature is attributed to the entry of the fluoride ions into the glass network mainly substitutionally in place of oxygen ion. The increase in dc electrical conductivity in the present glasses with increase in the fluorine ions is due to the mixed contribution of the positively charged lithium cations throughout the glass network and the negatively charged fluorine, which may act as impurity and/or as terminal non-bridging halide ion. Infrared and Raman spectroscopic results indicate that the glass network consists of BiO₆ octahedral and BiO₃ pyramidal units.     

Magnetic properties of partially crystallized Na2OFe2O3SiO2 glass

The magnetic properties of partially crystallized glasses of the Na₂OFe₂O₃SiO₂ system which had undergone thermal treatments of different durations and intensities leading to phase separation, have been measured in order to investigate the influence of magnetic grain growth. Magnetic moments were evaluated at liquid helium temperature in fields up to 76 kOe. The magnetic susceptibilities of some of the samples have been measured between 4.2 and 300 K. They were shown to depend strongly on the dimensions of the grains, i.e. on the thermal treatment of each sample. The anomalous values observed are discussed in terms of the apparent presence of superantiferromagnetism superimposed on the contribution of paramagnetic Fe³⁺ ions dispersed in the amorphous matrix.     

Crystallization of 2(Ca,Sr,Ba)O-TiO2-2SiO2 composition glasses

Crystallization was examined for glasses having chemical composition of 2(Ca,Sr,Ba)O-TiO₂-2SiO₂ in which the CaO/SrO/BaO molar ratio varied. Powdered glass samples were pelleted into disks and sintered at 950 °C for 2 h. The major phase precipitated in the sintered samples was (Ca,Sr,Ba)₂TiSi₂O₈ and minor phase of perovskite such as CaTiO₃ or SrTiO₃ increased with CaO content in the samples containing more than 40 mol% of CaO in total CaO+SrO+BaO. Three regions having different slopes were found in linear relationships between SrO mol% and exothermal peak temperature on DSC curves or d[0 0 2] values determined by powder XRD method. These facts suggested that the major phase precipitated in each region was a solid solution containing a different amount of CaO, SrO, BaO and that these compositions varied depending on SrO content in the sample. The micro-crystalline structure, which could be useful in fabricating a dielectric dense body, was observed for samples containing 30-70 mol% of SrO.