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.     

Structure and properties of glasses in ZnO-P2O5-TeO2 system

Glasses in the ternary ZnO-P₂O₅-TeO₂ system were prepared and studied in two compositional series (100 − x)[0.5ZnO-0.5P₂O₅]-xTeO₂ (X-series) and 50ZnO-(50 − y)P₂O₅-yTeO₂ (Y-series) within the concentration range of x = 0-60 and y = 0-40 mol% TeO₂. Their structure was studied by Raman and ³¹P MAS NMR spectroscopies. The incorporation of TeO_x units into the structural network is associated with the depolymerisation of phosphate chain structure as revealed by both methods. At a high TeO₂ content isolated PO₄ tetrahedra are formed in the structure of glass series Y, while diphosphate O₃P-O-PO₃ groups are present in the structure of the glass series X. In the structure of glass series Y tellurium atoms form predominantly TeO₃ trigonal pyramids, whereas in the X glass series TeO₄ trigonal bipyramids prevail in the glass structure. The addition of TeO₂ to the parent zinc metaphosphate glass results in a decrease of glass transition temperature in both compositional series associated with the replacement of stronger P―O bonds by weaker Te―O bonds.     

Optical Properties of Bi2O3-TeO2-B2O3 Glasses

Glasses of the Bi₂O₃-TeO₂-B₂O₃ ternary system were developed and their linear and nonlinear optical properties were investigated. The absorption edges of these glasses were found to be 367-384 nm with a good transmittance in visible wavelength, although they exhibit the refractive indices as high as 1.98-2.12 at 633 nm. The absorption edges are quite steep and they are analyzed by the Urbach theory. The obtained Urbach energies of these glasses are 73-79 meV which are comparable to silica glasses. The high refractive index and its glass composition dependency are discussed according to the basics of the electronic polarizability and optical basicity. The high third order nonlinear susceptibility χ⁽³⁾ = 2.0 × 10^− 12 esu at 800 nm was also obtained in the 36Bi₂O₃-18TeO₂-46B₂O₃ glass.     

Structure and crystallization of potassium titanium phosphate glasses containing B2O3 and SiO2

Transparent glasses composition of which can be expressed by the formula: (100−x) · (K₂O · 2TiO₂ · P₂O₅) · x(K₂O · 2B₂O₃ · 7SiO₂), where x=5, 10, 15 and 20 mol% (KTP-xKBS), were obtained by melt quenching technique. The structure and crystallization behavior of these glasses have been examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction. In spite of their nominal composition, the studied glasses exhibit a similar oxygen polyhedra distribution. However, significant differences were found in the trigonal BO₃ units amount. During DTA runs all the examined glasses devitrify in two steps. In the former, very small crystals of an unknown crystalline phase are produced. In KTP-5KBS and KTP-10KBS glasses anatase phase was also detected. Attempts were made in order to identify the unknown phase (UTP) for which a AB₃(XO₄)₂(OH)₆ Crandallite-type structure was proposed where the A, B and X sites were occupied by K, Ti and/or Al, and P, respectively. In the second devitrification step the crystallization of the KTiOPO₄ phase occurs while the UTP phase previously formed disappears. Isothermal heat treatments performed at temperature just above T_g have allowed one to obtain transparent crystal-glass nanocomposites, formed by crystalline nanostructure of the UTP phase uniformly dispersed in the amorphous matrix.     

Structure and electrical conductivity of new Li2O-CeO2-B2O3 glasses

Fourier transformation infrared spectra, density and DC electrical conductivity of 30Li₂O · xCeO₂⋅(70 − x)B₂O₃ glasses, where x ranged between 0 and 15 mol%, have been investigated. The results suggested that CeO₂ plays the role of network modifier up to 7.5 mol%. At higher concentrations it plays a dual role; where most of ceria plays the role of network former. The density was observed to increase with increasing CeO₂ content. The effect on density of the oxides in the glasses investigated is in the succession: B₂O₃ < Li₂O < CeO₂. Most of CeO₂ content was found to be associated with B₂O₃ network to convert BO₃ into B O₄⁻ units. The contribution of Li⁺ ions in the conduction process is much more than that due to small polarons. The conductivity of the glasses is mostly controlled by the Li⁺ ions concentration rather than the activation energy for CeO₂ > 5 mol%. Lower than 5 mol% CeO₂ the conductivity is controlled by both factors. The dependence of W on BO₄⁻ content supports the idea of ionic conduction in these glasses.     

Structural study of PbO-MoO3-P2O5 glasses by Raman and NMR spectroscopy

Glasses in the ternary system PbO-MoO₃-P₂O₅ were prepared in three compositional series (100 − x)[0.5PbO-0.5P₂O₅]-xMoO₃ (A), 50PbO-yMoO₃-(50 − y)P₂O₅ (B) and (50 − z)PbO-xMoO₃-50P₂O₅ (C) and their structure was studied by Raman and ³¹P NMR spectroscopies. In the compositional series (100 − x)[0.5PbO-0.5P₂O₅]-xMoO₃ homogeneous glasses were prepared in the concentration region of 0-70 mol% MoO₃. Their glass transition temperature increases with increasing MoO₃ content having a maximum at x = 50 mol% MoO₃. ³¹P MAS NMR spectra reveal that in the glass series (A) the incorporation of MoO₃ results in the shortening of phosphate chains and gradual transformation Q² units into Q² and Q⁰ units, prevailing in glasses with a high MoO₃ content. Octahedral structural units MoO₆ dominate in most glass compositions and they are present also in the structure of Pb(MoO₂)₂(PO₄)₂ compound corresponding to the glass composition 50Pb(PO₃)₂-50MoO₃. The analysis of Raman spectra of glasses of the (B) series with a high MoO₃ content showed the transformation of octahedral MoO₆ units into tetrahedral MoO₄ units.     

The effect of composition on UV-vis-NIR spectra of iron doped glasses in the systems Na2O/MgO/SiO2 and Na2O/MgO/Al2O3/SiO2

Glasses with the compositions xNa₂O · 10MgO · (90 − x)SiO₂, 10Na₂O · xMgO · (90 − x)SiO₂, 5Na₂O · 15MgO · xAl₂O₃ · (80 − x)SiO₂, xNa₂O · 10MgO · 10Al₂O₃ · (80 − x)SiO₂, 10Na₂O · 10MgO · xAl₂O₃ · (80 − x)SiO₂, 10Na₂O · 5MgO · 10Al₂O₃ · (80 − x)SiO₂ were melted and studied using UV-vis-NIR spectroscopy in the wavenumber range from 5000 to 30 000 cm⁻¹. At [Al₂O₃] > [Na₂O], the UV-cut off is strongly shifted to smaller wavenumbers and the NIR peak at around 10 000 cm⁻¹ attributed to Fe²⁺ in sixfold coordination gets narrower. Furthermore, the intensity of the NIR peak at 5500 cm⁻¹ increases. This is explained by the incorporation of iron in the respective glass structures.     

Physical properties of lead iron phosphate glasses containing Cr2O3

The influence of Cr₂O₃ on glass forming characteristics and physical properties of PbO-Fe₂O₃-P₂O₅ glasses has been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and impedance spectroscopy. Glasses of the general composition xCr₂O₃-(28.3-x)PbO-28.7Fe₂O₃-43.0P₂O₅, 0 ≤ × ≤ 10, (mol%) were prepared by conventional melt-quenching technique. The compositions containing up to 4 mol% Cr₂O₃ formed fully amorphous samples and their Raman spectra show systematic increase in the fraction of orthophosphate Q⁰ units with increasing Cr₂O₃ content and O/P ratio.On the other hand, compositions containing 8 and 10 mol% Cr₂O₃ partially crystallized during cooling and annealing to Fe₇(PO₄)₆, Fe₂Pb₃(PO₄)₄ and Cr₂Pb₃(PO₄)₄. A high tendency for crystallization of these melts is related to the high O/P (> 4) and Fe²⁺/Fe_tot (≈ 0.60) ratios.Electrical conductivity of xCr₂O₃-(28.3-x)PbO-28.7Fe₂O₃-43.0P₂O₅, 0 ≤ × ≤ 10, (mol%) compositions is independent of Cr₂O₃ and controlled entirely by the polaron transfer between Fe²⁺ and Fe³⁺ ions.     

Calculation and analysis of vibrational spectra of PbCl2-Sb2O3-TeO2 glass from first principles

Ternary PbCl₂-Sb₂O₃-TeO₂ system provides promising materials for photonic applications. Glasses in this system are thermally stable, their refraction index is about 2.2 and they are transparent from 400 nm up to 6 μm. The ab initio molecular dynamics (MD) simulations of xPbCl₂-10SbO_3/2−(90-x)TeO₂ glasses (x = 10, 20, 30, 40, and 50) were carried out using density functionals, the plane-wave basis set expansion, and the projector-augment waves (PAW). The resulting glassy structures were analyzed with the help of partial radial distribution functions (RDF) and partial coordination numbers. Good agreement with the available experimental data was confirmed. The axial and equatorial oxygen atoms of TeO₄ trigonal bi-pyramids were distinguished. Vibrational frequencies and their corresponding eigen-modes were found by diagonalization of the dynamical matrix. The simulated vibrational spectra were decomposed to determine the contributions from individual atomic species and some more complex structural features and compared with experimental Raman spectra. The spectral decomposition was carried out by projecting vibrational displacement vectors onto various normal modes of typical symmetric structural units. The method proved to be able to successfully interpret the experimental Raman spectra.     

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.     

Structural analysis and devitrification of glasses based on the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives

Glasses, whose basic composition was based on the CaO-MgO-SiO₂ system and doped with B₂O₃, P₂O₅, Na₂O, and CaF₂, were prepared by melting at 1400 °C for 1 h. Raman and infrared (IR) spectroscopy revealed that the main structural units in the glass network were predominantly Q¹ and Q² silicate species. The presence of phosphate and borate units in the structure of the glasses was also evident in these spectra. X-ray analysis showed that the investigated glasses devitrified at 750 °C and higher temperatures. The crystalline phases of diopside and wollastonite dominated, but weak peaks, assigned to akermanite and fluorapatite, were also registered in the diffractograms. The presence of B₂O₃, Na₂O, and CaF₂ had a negligible influence on the assemblage of the crystallized phases, but it caused a reduction of crystallization temperature, comparing to similar glasses of the CaO-MgO-SiO₂ system.     

Phase separation and crystallization in the system SiO2-Al2O3-P2O5-B2O3-Na2O glasses

The phase separation and crystallization behavior in the system (80 − X)SiO₂ · X(Al₂O₃ + P₂O₅) · 5B₂O₃ · 15Na₂O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al₂O₃-P₂O₅-SiO₂ and forms a continuous phase. Glasses containing a larger amount of Al₂O₃-P₂O₅ (X = 40 and 50) readily crystallize and precipitates tridymite type AlPO₄ crystals. It is estimated that the phase separation occurs forming continuous Al₂O₃-P₂O₅-SiO₂ phase at first, and then tridymite type AlPO₄ crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively.     

Studies of some mechanical and optical properties of: (70 − x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Specimens of the glassy system: (70 − x)TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by the melt-quenching. An ultrasonic pulse-echo technique was employed, at 5 MHz, for measuring: the ultrasonic attenuation, longitudinal and shear wave velocities, elastic moduli, Poisson ratio, Debye temperature and hardness of the present glasses. It is found that the gradual replacement of TeO₂ by Li₂O in the glass matrix up to 30 mol% leads to decrease the average crosslink density and rigidity of prepared samples which affects the properties, i.e., the hardness, ultrasonic wave velocities and elastic moduli are decreased, while the Poisson ratio and the ultrasonic attenuation are increased. Also, optical absorption spectra were recorded in the range, 200-800 nm for these glasses. The obtained results showed that a gradual shift in the fundamental absorption edge toward longer wavelengths occurred. Values of both of the optical energy gap, E_opt, and width tails, ΔE, are determined. It is observed that E_opt is decreased and ΔE increased with the increase of Li₂O in the glass matrix up to 30 mol%. The compositional dependences of the above properties are discussed and correlated to the structure of tested glasses.     

Crystallization kinetics of the tungsten-tellurite glasses

The crystallization kinetics of the (1 − x)TeO₂-xWO₃ (where x = 0.10, 0.15, and 0.20, in molar ratio) glass system was studied by non-isothermal methods using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. DSC measurements were performed at different heating rates to study crystallization kinetics of the first crystallization reactions of the glasses. XRD analysis of tungsten-tellurite glasses heat-treated above the first crystallization temperatures revealed that the first crystallization peaks attributed to the α-TeO₂ and γ-TeO₂ crystalline phases for 0.90TeO₂-0.10WO₃ and 0.85TeO₂-0.15WO₃ samples and α-TeO₂ and WO₃ crystalline phases for the 0.80TeO₂-0.20WO₃ sample. Avrami constants, n, calculated from Ozawa equation, were found between 1.14 and 1.44. The activation energies, E_A, for the first crystallization reactions were determined by using the modified Kissinger equation as 379 kJ/mol, 288.1 kJ/mol and 228.8 kJ/mol, for 0.90TeO₂-0.10WO₃, 0.85TeO₂-0.15WO₃ and 0.80TeO₂-0.20WO₃ glasses, respectively.     

Dielectric analysis of tungsten-phosphoniobate 20A2O-30WO3 -10Nb2O5 -40P2O5 (A = Li, Na) glass-ceramics

New phosphate glasses of the quaternary system A₂O-Nb₂O₅-WO₃-P₂O₅, where X = Li and Na were prepared by the melt-quenching method. The introduction of WO₃ in the glass composition was based on the proposal of analysing the effect of the diminishing of the molar amount of the alkaline oxide and thus decreasing the molar ratio between network modifiers and network formers (M/F).In the present work we present the preparation of 20A₂O-30WO₃-10Nb₂O₅-40P₂O₅ (A = Li, Na) transparent glasses. These glasses were heat-treated in air, at 550 °C and 650 °C for 4 h. The structure of the obtained samples was studied by X-ray powder diffraction (XRD) and Raman spectroscopy and the morphology by scanning electron microscopy (SEM). The dc (σ_dc), ac (σ_ac) conductivity and dielectric spectroscopy measurements were performed in the function of the temperature and were related with the structural changes of the glass structures.     

Density-structure correlations in Na2O-CaO-P2O5-SiO2 bioactive glasses

Relations for Na₂O-CaO-SiO₂ glasses have been developed to calculate the density of Na₂O-CaO-P₂O₅-SiO₂ bioactive glasses. The calculation makes use of NMR results of O’Donnell et al. indicating that P₂O₅ forms a separate phase, containing Na₃PO₄ and Ca₃(PO₄)₂, in the investigated glasses. The volume of the silicate units is the same as that found in Na₂O-CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂ glasses. Similarly, the volume of PO₄ units is equivalent to that in Na₃PO₄ and Ca₃(PO₄)₂. Calculated densities are consistent with the experimental data.     

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.     

Investigation of infrared emission and lifetime in Tm-doped 75TeO2:20ZnO:5Na2O (mol%) glasses: Effect of Ho and Yb co-doping

In this paper we describe fabrication and characterization of rare-earth-doped active tellurite glasses to be used as active laser media for fiber lasers emitting in the 2 μm region. The base composition is (mol%): 75TeO₂-20ZnO-5Na₂O with different concentrations of Tm³⁺, Yb³⁺ and Ho³⁺ as dopants or co-dopants. Optical properties of doped glasses were studied and pumping at 800 nm and at 980 nm were tested in order to compare the efficiency of two pumping mechanisms. Optical characterization carried out on glasses containing only Tm³⁺ ions indicated the optimum concentration of Tm₂O₃ in terms of emission efficiency as 1 wt%. The addition of 5 wt% of Yb₂O₃ to Tm³⁺-doped glasses led to the best results in terms of intensity of fluorescence emission and of lifetime values. Yb and Ho co-doped Tm-tellurite glass was measured in emission.     

Effect of pressure on the refractive index and relative density of the CaO · Al2O3 · 6SiO2 glass

The refractive index for glass of the CaO · Al₂O₃ · хSiO₂ system with х = 6 in the range of pressures up to 6.0 GPa was measured using a polarization-interference microscope and an apparatus with diamond anvils. The changes in the relative density characterizing the compressibility of glass were estimated from the measured refractive indices within the framework of the theory of photoelasticity. The data were compared with the previous data for glasses of the same system with х = 2 and 4. The most compressible of the three glasses in the range 2.0-6.0 GPa was the CaO · Al₂O₃ · 6SiO₂ glass. For glasses with х = 2, 4 and 6 we calculated the degrees of polymerization of silicon-aluminum-oxygen network, NBO/T (NBO - non-bridging oxygen), which are determined as the ratio of the number of gram-ions of non-bridging oxygen atoms to the total number of gram-ions of network formers. The structure-chemical parameter NBO/T was calculated with due regard for the formation of triclusters and highly coordinated aluminum. The degree of polymerization of the CaO · Al₂O₃ · хSiO₂ glasses increases with increasing х, which agrees with the change of their relative density under pressure.     

The glass transition temperature and infrared absorption spectra of: (70−x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Glasses of the system: (70−x) TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (T_g) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO₂ by Li₂O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm⁻¹. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.