Thermodynamic mixing properties of liquids in the system Na2O-SiO2

Enthalpies of fusion have been measured by differential scanning calorimetry for a Na₂O-SiO₂ system at 50, 66.6, and 74.4 mol% SiO₂. Enthalpies of mixing of liquids obtained from different calorimetry techniques are critically evaluated. The data on calorimetric enthalpy, activity of Na₂O, cristobalite liquidus, and immiscibility gap are used to determine the enthalpy and entropy of mixing of sodium-silicate liquids are determined as a function of composition by the least squares method. The derived mixing properties are based only on the experimental data and are independent of any assumption about the structure and chemical species in liquids. The enthalpy of mixing has a minimum value of −120 kJ/mol at 35-40 mol% SiO₂ and is convex upward around 80-90 mol% SiO₂. The entropy of mixing have a maximum value of + 6 J/K-mol at 75 mol% SiO₂, and it decreases with the SiO₂ content to −5 J/K-mol at 40 mol% SiO₂. This decrease in entropy can be accounted for by ideal mixing of Q⁴, Q³, and Q^{0 + 1 + 2} (= Q⁰ + Q¹ + Q²) species in the liquids and is responsible for the negative temperature dependence of the partial molar Gibbs energy of mixing of Na₂O, observed in activity measurements. Comparison of the present results with previous values suggests that a quasi-chemical model and the Adam-Gibbs model overestimate the configurational entropy of mixing of liquids.     

Improvement of the Tm:H4 level lifetime in silica optical fibers by lowering the local phonon energy

The role of some glass network modifiers on the quantum efficiency of the near-infrared fluorescence from the ³H₄ level of Tm³⁺ ion in silica-based doped fibers is studied. Modifications of the core composition affect the spectroscopic properties of Tm³⁺ ion. Adding 17.4 mol% of AlO_3/2 to the core glass caused an increase of the ³H₄ level lifetime up to 50 μs, 3.6 times higher than in pure silica glass. The quantum efficiency was increased from 2% to approximately 8%. On the opposite, 8 mol% of PO_5/2 in the core glass made the lifetime decrease down to 9 μs. These changes of Tm³⁺ optical properties are assigned to the change of the local phonon energy to which they are submitted by modifiers located in the vicinity of the doping sites. Some qualitative predictions of the maximum achievable quantum efficiency are possible using a simple microscopic model to calculate the non-radiative de-excitation rates.     

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.     

Investigation on dielectric relaxations of PVP-NH4SCN polymer electrolyte

Poly (N-vinyl pyrrolidone) (PVP) and ammonium thiocyanate (NH₄SCN) based polymer films with different compositions have been prepared by solution casting technique. The amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis confirms the complex formation of the polymer with the salt. The conductivity analysis shows that the 20 mol% ammonium thiocyanate doped polymer electrolyte has high ionic conductivity and it has been found to be 1.7 × 10⁻⁴ S cm⁻¹, at room temperature. From the admittance plot, the activation energy has been found to be low for 20 mol% salt doped polymer electrolyte. The dielectric behavior has been analyzed using dielectric permittivity (ε^∗), dissipation factor (tan δ) and electric modulus (M^∗) of the samples.     

Preparation and optical properties of titania-doped hybrid polymer via anhydrous sol-gel process

Incorporation of metal alkoxides (Ti, Zr, etc.) for tuning the optical properties of silica glasses by the sol-gel process is of significant interest for optical applications. In this paper, we report an anhydrous sol-gel process for preparation of photosensitive titania-doped hybrid glassy polymer with good homogeneity and high doping concentration (TiO₂ up to 40 mol%). The process consists of two steps: in the first step methacryloxypropyltrimethoxysilane (MPS) is hydrolyzed by boric acid through ligand exchange reaction (OH↔OR) under anhydrous conditions; and in the second step dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET) were added to condense with the silanols formed in the first step. The optical properties of the synthesized hybrid polymer were studied, and results showed that the hybrid material has low OH absorption, low optical losses (0.45 dB/cm at 1550 nm and 0.16 dB/cm at 1310 nm respectively), and good thermo-optical linearity with tuneable refractive index. The effect of TiO₂ doping in reducing the OH concentration of the hybrid material was observed, and the mechanism for this effect is discussed.     

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.     

Development of optical nonlinearity, high dielectric constant and ferromagnetic behavior in a silicate glass nanocomposite by suitable heat treatment

We have explored the development of multifunctionalities viz, optical nonlinearity, high dielectric constant and ferromagnetic behavior in a nanostructured silica based glass of 14.0Na₂O, 26.0BaO, 26.0TiO₂, 16.0B₂O₃, 17.0SiO₂, 1.0NiO (mol%) composition. A heat treatment at 863 K for 4 h led to nonlinear refractive index and absorption coefficients at wavelength 800 nm of 0.11 × 10⁻¹⁹ m²/W and 1.15 × 10⁻³ cm/GW, respectively. A heat treatment at 1073 K for 2 h followed by 1113 K for 3 h increased the dielectric constant from 11 to 50, apparently due to the formation of nanocrystals of BaTiO₃ within the glass medium. Glass samples reduced at 923 K for 1 h exhibited ferromagnetic behavior due to the presence of nickel nanoparticles.     

Optical properties of fluorine-substituted zinc bismuth phosphate glasses

The effects of the substitution of fluoride ions for oxide ions on the thermal and optical properties of ternary ZnO-Bi₂O₃-P₂O₅ glass with low-P₂O₅ content (20-25 mol%) were investigated. Fluoride ions were introduced into the glass up to about 12 mol% as ZnF₂. Raman spectra indicated that fluoride ions were substituted for oxide ions connected with bismuth ions. Deformation and glass transition temperatures decreased monotonically with fluorine concentration. The absorption edge shifted toward higher energies with increasing fluorine concentration by about 0.3 eV for 12 mol% ZnF₂ substitution. The blue shift of the absorption edge is attributable to two effects. One was a blue shift of an absorption band which was observed as a peak at 4.7 eV in the reflection spectra and was attributed to the spin forbidden 6s-6p interband transition in Bi³⁺ ions. The blue shift originates from a change in electron-donating ability through anions as expected from electronegativity or optical basicity. Another is a disappearance of a shoulder at around 4.3 eV in the reflection spectra. The latter was the major reason for the large blue shift of the absorption edge energy, because the band relating to the 4.3 eV shoulder is close to the absorption edge.     

Population dynamics of the F4 and H4 levels in highly-doped Tm:ZB(L)AN glasses

Population dynamics of the ³F₄ and ³H₄ levels in Tm³⁺ doped ZB(L)AN glasses was studied for Tm³⁺ concentrations from 0.5 to 12 mol%. Fluorescence waveforms from these levels were measured at 1.8 μm (³F₄) and 800 nm (³H₄) with both direct and indirect pumping. Decay from the ³F₄ level was found to be exponential with non-radiative decay rates proportional to the square of the Tm concentration. This indicated a process of energy migration by diffusion within the excited Tm³⁺ ions followed by quenching at sites to which the ions could migrate. The decay of the directly pumped ³H₄ level exhibited both exponential and non-exponential behavior depending on the concentration. For the lowest concentration (0.5 mol%) the decay was exponential, but at concentrations of 1, 2, 4 and 6 mol% the decay waveforms were distinctly non-exponential. The non-exponential waveforms could be fitted by the Yokota-Tanimoto model for diffusion of excited donors and dipole-dipole interactions with acceptors. This model produced values for C_DD and C_DA, the donor-donor and donor-acceptor energy transfer parameters, respectively. At the higher concentrations (8, 10, 12 mol%) the waveforms were exponential with decay rates from which the cross-relaxation parameter for the process ³H₄, ³H₆ → ³F₄, ³F₄ was obtained. When the ³F₄ level is pumped at 1660 nm, the decay of the ³H₄ level confirmed the influence of the up-conversion energy transfer process ³F₄, ³F₄ → ³H₄, ³H₆.     

Optical and electrical properties of lithium doped nickel oxide films deposited by spray pyrolysis onto alumina substrates

Non-doped and lithium doped nickel oxide crystalline films have been prepared onto quartz and crystalline alumina substrates at high substrate temperature (600 °C) by the pneumatic spray pyrolysis process using nickel and lithium acetates as source materials. The structure of all the deposited films was the crystalline cubic phase related to NiO, although this crystalline structure was a little bit stressed for the films with higher lithium concentration. The grain size had values between 60 and 70 nm, almost independently of doping concentration. The non-doped and lithium doped films have an energy band gap of the order of 3.6 eV. Hot point probe results show that all deposited films have a p-type semiconductor behavior. From current–voltage measurements it was observed that the electrical resistivity decreases as the lithium concentration increases, indicating that the doping action of lithium is carried out. The electrical resistivity changed from 10⁶ Ω cm for the non-doped films up to 10² Ω cm for the films prepared with the highest doping concentration.     

Sol-gel synthesis of erbium-doped yttrium silicate glass-ceramics

Yttrium silicate glasses and glass-ceramics were prepared by the sol-gel process. Yttrium nitrate was added to tetraethyl orthosilicate in amounts representing between 0.2 and 20 mol%, as well as amounts corresponding to the disilicate composition. Some samples were doped with erbium acetate. The solutions underwent gellation in 2-7 days and were dried for 2 weeks. Differential thermal analysis was used to design a multi-step heat treatment to 1000 °C to densify samples to transparent or translucent monoliths. Above 1000 °C, samples crystallized to yttrium disilicate and cristobalite. Phase separation before crystallization influenced the formation of the crystal phases.     

Concentration quenching of fluorescence from the (P0 + P1) manifold in heavily-doped Pr: ZBAN glasses

Fluorescence waveforms from the (³P₀ + ³P₁) manifold in Pr³⁺ doped ZBAN glass at wavelengths of 520, 635 and 695 nm were measured for Pr³⁺ concentrations from 4 to 12 mol%. The waveforms were found to be non-exponential with decay rates rapidly increasing with Pr³⁺ concentration and independent of whether the ³P₀ or the ³P₁ level was excited. The multipolar energy transfer model was used to analyse the waveforms and this showed that concentration quenching was due to cross-relaxation by dipole-dipole interaction. The critical concentration, at which the cross-relaxation rate equals the intrinsic decay rate, was found to be of 2.06 × 10²⁶ m⁻³ (1.20 mol%). There was no evidence of excitation diffusion for Pr³⁺ concentrations of up to 12 mol%.     

Dependence of fluorescence properties on substitution of BaF2 for BaO in barium gallo-germanate glass

3.5 mol%, 6.5 mol%, 9.5 mol%, and 12.5 mol% BaF₂ were gradually substituted for BaO in 0.3 mol% Tm₂O₃ doped 12.5 BaO-12.5 Ga₂O₃-75 GeO₂ (BGG) glasses to study the effect of the substitution on the OH⁻ elimination and emission properties. The FTIR spectral demonstrated that the substitution effectively eliminated OH⁻ groups and 9.5 mol% BaF₂ was enough for the OH⁻ elimination. The J-O parameters of all the samples were calculated according to J-O theory. The calculation showed that the Ω₂ parameter decreased monotonically with BaF₂ content increasing, while Ω₄ and Ω₆ did not change much. The radiative lifetime increased while BaF₂ content increased as well. The emission cross section of ³F₄ → ³H₆ transition was calculated by the F-L formula. However, it decreased with the gradual BaF₂ addition.

Research Highlights

? OH⁻ groups were eliminated by the substitution of BaF₂ for BaO in (BGG) glass. ? The optimal substitution level of BaF₂ was 9.5 mol% for OH⁻ elimination. ? The Ω₂ parameter decreased monotonically by the elimination. ? The emission cross section of ³F₄ → ³H₆ transition was decreased by the substitution.     

Thermal, chemical, optical properties and structure of Er-doped and Er/Yb-codoped P2O5-Al2O3-ZnO glasses

This study was explored in series of the optical, thermal, and structure properties based on 60P₂O₅-10Al₂O₃-30ZnO (PAZ) glasses system that doped with varied rare-earth (RE) elements Yb₂O₃/Er₂O₃. The glass transition temperature, softening temperature and chemical durability were increased with RE-doping concentrations increasing, whereas thermal expansion coefficient was decreased. In the optical properties, the absorption and emission intensities also increase with RE-doping concentrations increasing, When Er₂O₃ and Yb₂O₃ concentrations are over than 3 mol% in the Er³⁺-doped PAZ system and Yb³⁺-doped concentration is over than 3 mol% for Er³⁺/Yb³⁺-codoped PAZ system, the emission intensity significantly decreases presumably due to concentration quenching, formation of the ions clustering, and OH⁻ groups in the glasses network. It is suggested that the maximum emission cross-section (σ_e) is 7.64 × 10^− 21 cm² at 1535 nm is observed for 3 mol% Er³⁺-doped PAZ glasses. Moreover, the maximum σ_e × full-width-at-half-maximum is 327.8 for 5 mol% Er³⁺-doped PAZ glasses.     

Non-Debye excess heat capacity and boson peak of binary lithium borate glasses

The non-Debye excess heat capacities of binary lithium borate glasses with different Li₂O compositions of x = 8, 14 and 22 (mol%) are investigated to understand origin of the boson peak. The low-temperature heat capacities are measured between 2 and 50 K by a relaxation calorimeter. The experimental non-Debye heat capacities with x = 14 is successfully reproduced using the excess vibrational density of states measured by inelastic neutron scattering. This finding indicates that the non-Debye heat capacities of lithium borate glasses originate from the excess vibrational density of states measureable by inelastic neutron scattering. Moreover, it is demonstrated that all of the excess heat capacity spectra lie on a single master curve by the scaling using boson peak temperature and intensity.     

The structural role of titanium in Ca-Sr-Zn-Si/Ti glasses for medical applications

Glasses for medical applications are used in particulate form or as a cement component. This work was undertaken to determine structural changes in 0.48SiO₂-0.36ZnO-0.12CaO-0.04SrO glass when the SiO₂ is substituted with 5 mol% increments of TiO₂. X-ray Diffraction (XRD) was used to determine the presence of crystallinity. This occurred after additions of 20 mol% TiO₂. Differential Thermal Analysis (DTA) and Network connectivity (NC) calculations determined that by increasing the TiO₂ content, the T_g and NC reduced (T_g 670 °C to 632 °C, NC 1.83 to −1.14) suggesting that TiO₂ acts as a modifying oxide. X-ray Photoelectron Spectroscopy (XPS) was used to determine the glass composition and the relative fraction of Bridging Oxygens (BO) to Non-Bridging Oxygens (NBO). XPS revealed that by increasing the concentration of TiO₂, the NBO concentration increases, further suggesting the modifying role of Ti. The NBO/BO ratio was found to increase from 1.2 to 9.0 as the TiO₂ content increased from 0 to 20 mol% additions. Raman spectroscopy was used to determine the Q-Structure of the glass series and found that the addition of TiO₂ reduced the Raman shift from containing predominantly Q¹/Q² units when no Ti was present to Q⁰/Q¹ with TiO₂ additions.     

Effect of CeO2-doping on surface and catalytic properties of CuO-ZnO system

The effect of doping CuO-ZnO system with CeO₂ on its surface and catalytic properties was investigated using nitrogen adsorption at −196 °C, EDX technique and catalysis of CO oxidation by O₂ at 100-200 °C. Pure mixed solids were prepared by thermal decomposition of copper/zinc mixed hydroxides at 400 °C. The doped solids were obtained by impregnating a known mass of mixed hydroxides with calculated amount of cerium ammonium nitrate followed by drying then calcination at 400 °C. The dopant concentration was 1.5, 3.0 and 4.5 mol% CeO₂. The results revealed that CeO₂-doping modified the surface atomic Cu/Zn ratio of the system investigated and changed the crystallite size of both CuO and ZnO phases. The increase of the amount of dopant added changed the major phase present. This treatment decreased the specific surface area of doped solids. The doping process modified also the catalytic activity in a manner dependent on both mode of preparation and dopant concentration. However, CeO₂-doping did not modify the mechanism of the catalytic reaction but changed the concentration of catalytically active sites involved in the catalyzed reactions.     

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.     

Thermodynamics of the Cu/Cu-redox equilibrium in soda-silicate and soda-lime-silicate melts

The thermodynamics of the redox equilibrium of Cu⁺/Cu²⁺ were determined by square-wave voltammetry in glass melts with the base mol% compositions x Na₂O · (100 − x) SiO₂ (x = 15, 20, 26 and 33) and (26 − x) Na₂O · x CaO · 74 SiO₂ (x = 0, 5, 10 and 15) doped with 1 mol% CuO in the temperature range from 850 to 1150 °C. All recorded voltammograms showed two maxima attributed to the reductions of Cu²⁺ to Cu⁺ and Cu⁺ to metallic copper. Both peaks are shifted to smaller potentials with decreasing temperature. With increasing melt basicity, the [Cu⁺]/[Cu²⁺]-ratio first increases, and remains constant for optical basicities >0.56. The effect of composition on the redox equilibrium is explained by the incorporation of both Cu⁺ and Cu²⁺ in octahedral coordination into the melt structure.     

Glass formation in the MoO3-CuO-PbO system

Glasses in the MoO₃-CuO-PbO system are obtained at high cooling rates (10⁴-10⁵ K/s) and characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), infrared (IR) and X-ray photoelectron spectroscopy (XPS). Two glass formation regions are determined: one with compositions having a high MoO₃ content (50-80 mol%) and the other in the PbO-rich compositions (65-80 mol%). In the region of MoO₃-rich compositions the building units of the amorphous network are МоО₆, МоО₄ and CuO₄ groups. For these high MoO₃ contents and respectively low PbO concentrations, the lead oxide is supposed to act as a network modifier while at high content PbO is found to be the main glass network former. In latter case the structure of glasses is formed by chains of PbO_n (n = 3, 4) polyhedra, between which there are isolated MoO₄ and CuO₄ complexes. IR and XPS data reveal the existence of Mo-O-Mo, Mo-O-Me(Me’) (where Me = Cu²⁺, Cu¹⁺ and Me’ = Pb) and Me(Me’)-O-Me(Me’) bonds in the amorphous network. Surprising result is found for low PbO content (10 mol%) where the lead oxide acts as glass network modifier: the actual MoO₃ content drops strongly which is accompanied with a significant increase of the actual CuO content with respect to their nominal MoO₃-CuO composition. Such effect is not observed in PbO-rich composition (70 mol%) where PbO has a role of network former.