Glass formation range in the SeO2-TeO2-V2O5-MoO3 system

The glass forming region in the quaternary system under increased oxygen pressure and at a slow melt cooling rate (2 to 2.5° C min^-1) has been determined. The stable glasses are located in the central part of the system but nearer to the SeO₂-TeO₂ side. The structural units of these two glass formers are of decisive importance in building up the glass lattice. Infrared spectra of selected compositions from the glass forming region are taken. From the data obtained for the binary glasses in the TeO₂-V₂O₅, TeO₂-SeO₂, TeO₂-MoO₃, V₂O₅-MoO₃ systems and the spectra of the four component compositions, it is shown that the basic structural units participating in the glass lattice formation are the SeO₃, VO₅, TeO₄ and TeO₃ groups. Structural models are proposed: glasses in the SeO₂ direction possess laminar and chain structure, while with increase of TeO₂ concentration, a three-dimensional structure is built up.     

Structural and spectroscopic effects of Ag–Eu3+ codoping of TeO2–PbO glass ceramics

Structural and spectroscopic behavior of TeO₂–PbO–Eu₂O₃ glass ceramics containing small amounts of Ag₂O (0.5 mol%) or metallic Ag nanoparticles (AgNPs) (0.33 mol%) have been studied by varying their Eu₂O₃ content (0–10 mol%). The structural behavior of these samples was investigated by means of X-ray diffraction (XRD), SEM microscopy, and Fourier transform infrared (FTIR) spectroscopy. The average unit-cell parameters, crystallites size, and the quantitative ratio of the crystallographic phases in the samples were evaluated based on XRD data. FTIR spectroscopy data revealed that the TeO₃ and TeO₄ are the main structural units of these glass ceramics and their ratio, TeO₃/TeO₄, changes as function of the europium oxide content and the codoping of the samples. Luminescence spectroscopy measurements evidenced the important peaks located at 438, 550, and 722 nm due to the Pb²⁺ ions and at 589 and 611 nm due to the Eu³⁺ ions present in the studied samples. The presence of AgNPs in the studied glass ceramics determines a considerable enhancement of the luminescence bands of Eu³⁺ ions from 589 and 611 nm.     

Glass formation tendency in the system SeO2-Ag2O-B2O3

The glass formation regions in the system SeO₂-Ag₂O-B₂O₃ have been determined using the melt quenching method of evacuated silica ampoules. The structural units forming the amorphous network have been established by IR spectroscopy. The presence of SeO₃ (ν = 820 cm⁻¹; 760-750 cm⁻¹), BO₃ (ν = 1340, 1270 cm⁻¹) and BO₄ (ν = 1050 cm⁻¹) units has been confirmed. Crystallization of Ag₂SeO₃ only has been observed in a wide concentrate region near the glass formation boundary. A model explaining the unsatisfactory glass formation ability in the system investigated has been developed. It has been suggested that Ag⁺ ions are predominantly located near the selenite units, which stimulates the formation of isolated SeO₃ groups. The transformation of BO₃ into BO₄ units is hindered by the absence of free Ag⁺ ions near the borate units.     

Chemical and sol–gel processing of tellurite glasses for optoelectronics

Recent developments in the application of sol–gel processing technology for tellurite glass systems are reviewed and reported. The processing of telurite glasses via sol–gel entails some difficulties, mainly due to the anomalously high reactivity of Te(IV) alkoxides toward hydrolysis. Although conventional approaches to steric stabilisation of the alkoxides is not successful for these compounds, various successful approaches have been developed which allow the fabrication of transparent films from these precursors. In particular, diol complexation, chemical liberation of water from esterification processes and peptisation methods have been demonstrated. Other successful approaches involve the use of Te(VI) alkoxides and acids as precursors, with TeO₂ based glasses being formed via TeO₃ intermediates which liberate oxygen during heat treatment. One drawback with all these methods is the inherent thermal instability of the sol–gel derived material, which leads to both the liberation of free tellurium and devitrification of the glass on heat treatment. However this problem is less significant when Te(VI) precursors are used. The fabrication of multicomponent tellurite glasses by sol–gel approaches is very successful. Systems such as TeO₂–TiO₂ and TeO₂–PbO–TiO₂ have been successfully fabricated, and exhibit much greater resistance to devitrification allowing fully dense, transparent glasses to be produced.     

Silver Diffusion and Clustering in Oxyfluoride Glasses Investigated by Molecular Dynamics Simulations

Glasses with compositions (97 – x)[PbF₂:GeO₂]–3Al₂O₃–xAg₂O, with the PbF₂:GeO₂ ratio equals to 1.5 and x varying from 0 to 3%, form silver surface films after thermal treatment near the glass transition temperature. The NPT molecular dynamics simulations of a glass composition 56.4PbF₂–37.6GeO₂–3Al₂O₃–3Ag₂O have been performed, where 0, 20, 40, 60, and 100% of the Ag⁺ ions were reduced to Ag by the fluoride ions. The simulations showed that the silver atoms aggregate into clusters of increasing numbers and sizes as the silver atoms content increases. In addition, the silver atoms diffusion coefficients are at least one order of magnitude larger than the fastest ion in the matrix. These results are consistent with the rapid formation of the metallic surface film observed experimentally.     

Characterization of Fe<Superscript>3+</Superscript>-doped silver phosphate glasses

The relationship among the composition, structure and selected properties for five series of silver phosphate glasses containing 0, 5, 10, 15 and 20 wt% Fe₂O₃ has been investigated. The synthesized glasses have been characterized using different experimental techniques. X-ray diffraction studies revealed that the glasses are amorphous in nature. IR spectral studies have shown the presence of characteristic P–O–P linkages of linear phosphate chains, presence of O–P–O units in the phosphate tetrahedral and the formation of P–O–Fe bonds in the doped glass. It is also confirmed that due to doping of Fe₂O₃, loosening of glassy structure occurred and the glass became more disordered. Differential scanning calorimetric (DSC) studies revealed that glass transition temperature increased with Fe₂O₃ concentration. Scanning electron microscopic studies have shown that Fe₂O₃ doping modifies the microstructures of the glass and at lower concentration of dopant, a nanostructure is obtained. Electrical conductivity measurements from 303 to 373 K in a frequency range from 100 Hz to 5 MHz have indicated that all glasses are ionic conductors with Ag⁺ ions as the charge carrier. Fe₂O₃ doping in silver phosphate glass increased the electrical conductivities. Results have shown that dielectric constants increased with the increase of temperature at all the frequencies; a.c. and d.c. conductivities have been separated and a Cole–Cole plot is also drawn. Dielectric losses in all the glasses decreased with frequency at a particular temperature. It is found that Ag₂O–P₂O₅ glass doped with 5 wt% Fe₂O₃ gives high OCV value and the doped glass can be used as an electrolyte for solid-state batteries.     

Spectroscopic studies of TeO<Subscript>2</Subscript>–ZnO–Er<Subscript>2</Subscript>O<Subscript>3</Subscript> glass system

Series of glass based on the (80 − x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ≤ x ≤ 2.5 mol%) has successfully been made by melt quenching technique. The optical properties of glass have been investigated by means of IR and Raman spectroscopy. It is observed that as the Er₂O₃ content is being increased, the sharp IR absorption peaks are consistently shifted from 650 to 672 cm⁻¹ while the Raman shift intensity around 640–670 cm⁻¹ is decreases but increases around 720–740 cm⁻¹. It is found out that both phenomenons are related to the structural changes between the stretching vibration mode of TeO₄ tbp and TeO₃ tp, and bending vibration mode of Te–O bonds in the glass linkages.     

Glass formation in oxide-halide systems

Recently the halide and oxidechalide glasses have been the object of great interest because they are promising materials for optics. Up to now many unsolved problems exist in relation to their glass formation, chemical resistance and the thermal stability of these glasses. An object of our investigation is the study of the glass formation in halide systems with the participation of PbCl₂, NaCl, KCl, BaCl₂ and oxide-halide systems with the participation of the TeO₂. The ranges of glass formation in the systems: TeO₂-PbCl₂-NaCl-KCl and TeO₂-BaCl₂-CdCl₂-NaCl are determined at different cooling rates. Stable glasses possessing low melting temperature, good chemical resistance were prepared.     

Electrical switching and spectroscopic studies of silver-vanado-phosphate glasses

High field electrical switching studies on x Ag₂O − (50−x) P₂O₅ −50V₂O₅ glasses have been carried out as a function of sample thickness, composition and temperature. The I–V characteristic show that switching in these glasses is memory type. The switch voltages are found to decrease with increase of temperature, on the other hand, the voltages increase with the thickness of the sample. The experimental findings clearly reveal that switching in these glasses is a thermally assisted bulk effect. The results obtained are explained on the basis of formation of crystalline conducting channels. Another notable observation is that the glass with 15 mol% Ag₂O concentration only exhibits the switching property at room temperature. This aspect is examined in view of various structural groups present in these glasses with the help of spectroscopic studies; IR and MAS–NMR measurements have been carried out. IR studies of these glasses show characteristic absorption peaks corresponding phosphate and vanadium vibrations in the network. ³¹P MAS–NMR chemical shift show presence of [POO_3/2]⁰ and [POO_2/2O]⁻ groups.     

Incorporation of LiNbO3 crystals into tellurite glasses

Transparent tellurite glasses containing 5–10 m diameter LiNbO₃ crystals (3–7 wt%) have been successfully prepared using an incorporation method in which LiNbO₃ crystals are directly dispersed into the 80TeO₂-15Li₂O-5Nb₂O₅ glass. The dissolution behaviour of the LiNbO₃ crystals greatly depends on the Li₂O: Nb₂O₅ ratio in the matrix glasses. In the 80TeO₂-10Li₂O-10Nb₂O₅ matrix glass, the crystals remaining after incorporation have the composition LiNb₃O₈. A small difference in the refractive indices, n, between the TeO₂-based glasses (n=2.07) and the incorporated LiNbO₃ crystals (n=2.296) is a significant reason for the transparency. It is feasible to prepare the highly transparent TeO₂-based glasses containing a large amount of LiNbO₃ crystals by controlling the incorporation process.     

Preparation and structural studies in the (70 − x)TeO2–20WO3–10Li2O–xLn2O3 glasses

Quaternary tellurite glass systems (70 ? x)TeO₂–20WO₃–10Li₂O–xLn₂O₃ where x = 0, 1, 3 and 5 mol% and Ln are La, Pr, Nd, Sm, Er and Yb, respectively, have been prepared by the melt quenching technique. Densities of the obtained glasses were measured and the molar volume was calculated. IR absorption spectra of the present glass systems were determined at room temperature over the range of wavenumbers from 400–1,600 cm^?1. Raman spectra of the present glass samples were measured in the range of 30–1,030 cm^?1. Density, molar volume, IR and Raman spectra of the glasses were discussed by calculating average cross-link density, packing density, theoretically calculated Poisson’s ratio and number of bonds per unit volume of the studied glasses. Also, the quantitative interpretations were based on concentration of ions per unit volume of Te, Ln and O, short distance in nanometre between ions for (Te–O) of TeO₄ and TeO₃ groups, (W–O) of WO₄, WO₆ groups and calculated wavenumber, $ \bar{\upsilon } $ , for TeO₄ and TeO₃, respectively. The average stretching force constant that present in these quaternary glasses has been calculated in order to interpret the data obtained.     

Preparation chimioue et structure cristalline des tellurites de sodium et d'argent: Na2TeO3, Ag2TeO3

Sodium and silver tellurites are isotypic. The space group is $\text{P}\text{2}{}_1\text{a}$. For Ag₂TeO₃, the parameters of the monoclinic unit cell are: a = 7.000(2), b = 10.509(5), $\text{c}\text{= 4.911(2)}\text{A}\text{?}$, β = 91°51(5). The structures of sodium and silver tellurites has been determined. For Ag₂TeO₃, a R value of 0.047 is reached with 829 reflexions and for Na₂TeO₃ R = 0.024 with 1125 reflexions. The framework is built with MeO₆ edge sharing octahedra, Me = Ag,Te. Ag₂TeO₃ is a distortion of NaCl Structure.     

Optical and thermal characteristics of glasses based on TeO 2

Glass samples have been synthesized in quaternary system based on TeO ₂–oxide within composition, 85TeO ₂–5Nb ₂O ₅–5ZnO–5Ag ₂O, 68TeO ₂–5Nb ₂O ₅–20ZnO–7Na ₂O and [(75?x)TeO ₂–5Nb ₂O ₅–20ZnO–xPbO, x = 7, 18 mol%]. Structural characterization of the glasses was studied with respect to their thermal stability, refractive indices, third order nonlinear optical susceptibility, IR spectra and Vickers hardness. For four different prepared glasses, density in the range from 5·3744 to 6·0731 g· cm ^???1, the glass transition temperature (T _g) in the range from 326 to 350 °C and refractive indices, n, in the range from 2·1273 to 2·2123 at 435 nm and Vickers hardness, H _v, in the range from 2·91 to 3·44 GPa were determined. The value of third order nonlinear optical susceptibilities ${\vert} {\chi}^{\text{(3)}}{\vert} {\approx} $ 17·9 ·10^{??? 13} esu of glass within composition, 68TeO ₂–5Nb ₂O ₅–20ZnO–7PbO, was measured by using degenerate four-wave mixing (DFWM).     

Electrical and physicochemical properties of some Ag<Subscript>2</Subscript>O-containing lithia iron silica phosphate glasses

The present paper reports the influence of Ag₂O addition at the expense of Li₂O on the local structure of xAg₂O·(30 − x)Li₂O·10Fe₂O₃·10SiO₂·50P₂O₅ glass matrix (with x = 0, 0.5, 1, 1.5 and 2 mol %). The phosphate structural units of the network former are assessed from Fourier transform infrared (FT-IR) spectroscopy. The addition of Ag₂O to the glass network matrix ≤1 mol % leads to the occurrence of a depolymerization process of the phosphate structure and consequently, to the appearance of a distortion of the PO₄ tetrahedra. When the content of Ag₂O is increased from 1.5 up to 2 mol %, a remarkable polymerization process has been observed. The density, molar volume, microhardness and chemical durability have been investigated in order to study the effect of Ag₂O/Li₂O replacements on the physicochemical properties the studied glasses. The AC electrical properties are affected to a great extent with composition. These results are related to the internal structure of the glass samples. The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 100 Hz–100 kHz and the effect of compositional changes on the measured properties was investigated. Measurements showed that the electrical responses of glass samples were different and complex for interpretation. The increase of Ag₂O addition at the expense of Li₂O contents (from 0 to 1 mol %) led to increase the conductivity, dielectric constant and dielectric losses of samples. The addition of more Ag₂O at the expense of Li₂O (from 1.5 to 2 mol %), resulting into decreasing the conductivity, the dielectric constant and dielectric losses of the studied glasses. The experimental data of the glass samples were argued to the internal structure of the glasses and the nature and role-played by weakening or increasing the rigidity of the structure of the sample. It could be concluded, therefore, that the AC electrical properties of the samples were influenced by the distribution of its constituents, connectivity, and number of free charges.     

Effect of the introduction of vanadium pentaoxide in phospho-tellurite glasses containing gadolinium ions

A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption spectra were measured. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd₂O₃ causes a higher extent of network polymerization as far as x ≤ 15 mol% because the conversion of [TeO₄] to [TeO₃] structural units is supported by the increase of metaphosphate structural groups. While for x between 20 and 30 mol% Gd₂O₃ show some drastic structural modifications which lead to the increase in the glass fragility. Thus the addition of V₂O₅ resulted in gradual depolymerization of the phosphate chains and formation of short phosphate units, which are linked to vanadium through P–O–V bonds. The formation of P–O–V bonds increases the cross-link between the phosphate chains and the bending mode of Te–O–Te or O–Te–O linkages.     

Thermal stability and transport studies of (100 − 2x)TeO2-xAg2O-xWO3 (7.5 ≤ x ≤ 30) glass system

Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO₂-xAg₂O-xWO₃ (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO₃₊₁], [WO₄] units. Thermal properties such as the glass transition (T_g), onset crystallization (T_o), thermal stability (ΔT), glass transition width (ΔT_g), heat capacities in the glassy and liquid state (C_pg and C_pl), heat capacity change (ΔC_p) and ratios C_pl/C_pg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO₂-22.5Ag₂O-22.5WO₃ glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27-260 °C, the activation energy (E_act) values varied from 1.393 to 0.272 eV and for the temperature interval 170-260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10⁻⁹ to 1.47 × 10⁻⁶ S cm⁻¹.     

UV–vis spectroscopic studies of CaF2 photo-thermo-refractive glass

A photo-thermo-refractive glass based on the system Na₂O/K₂O/CaO/CaF₂/Al₂O₃/ZnO/SiO₂ doped with Ag₂O, CeO₂, SnO₂, Sb₂O₃ and KBr was investigated. This glass undergoes a permanent refractive index change after UV irradiation and subsequent two step heat treatment at temperatures above Tg. This is due to the formation of Ag metal clusters which act as nucleation centers for CaF₂ crystallization. Oxidation of Ce³⁺ by UV light is the initial reaction and acts as photosensitizer in the glass. The UV–vis absorption spectra during this photo-induced crystallization process were measured. The spectral components that form the absorption spectra of cerium were studied in detail by a band separation with Gaussian functions. Deconvolution of the cerium absorption bands shows an envelope of five spectral components for the trivalent cerium due to the 4f-5d transitions and two spectral components for the tetravalent cerium caused by charge transfer transitions. The effect of different dopants and melting conditions on the photo-thermal process were studied to investigate the influence of glass technology on the photoprocess.     

Oxygen gas-sensing behaviour of V2O5–SnO–TeO2 glass

The d.c. conductivity, σ, and the oxygen gas-sensing behaviour of V₂O₅–SnO–TeO₂ glass prepared by press-quenching were studied in argon and oxygen gas atmospheres at temperatures ranging from 303–473 K. The glass of 50V₂O₅·20SnO·30TeO₂ (mol %) was n-type semiconducting. The high-temperature conductivity was lower in oxygen and higher in argon than that in air. This was explained by the V⁴⁺ ions in the glass being oxidized by oxygen which had diffused into the glass, resulting in an increase in V⁵⁺ with time. The experimental relationship between σ and oxygen partial pressure, P _O2, agreed quantitatively with the theoretical relation σ ∝ P _O2 ^-1/4 . Changes in conductivity by switching the atmospheres between oxygen and argon gases were found to be reproducible. From the data of these dynamic changes, the oxygen gas sensitivity, S, at 473 K was obtained to be 1.3 in oxygen atmosphere. The dynamic changes could be quantitatively explained by an oxygen diffusion model. Throughout these discussions, the present tellurite glass was found to possess a potential applicability as an oxygen gas sensor. This revised version was published online in November 2006 with corrections to the Cover Date.     

Absorption and emission spectral analysis of Pr<Superscript>3+</Superscript>: tellurite glasses

This paper reports on the results concerning optical absorption and fluorescence properties of 60TeO₂–25ZnO–10BaO–4.5La₂O₃–0.5Pr₂O₃ (Pr³⁺: TZBL) glass. Both electronic (α_e) and vibrational (α_v) band edge cut-off wavelengths of the host glass (TZBL) have been evaluated from the measurement of its UV–Vis and IR transmission spectra. The glass studied has shown 80% transmittance throughout its optical window from 0.366 μm (α_e = 3.39 eV) to 6.30 μm (α_v = 0.197 eV). The FT-IR transmission spectra of Pr³⁺ doped and also reference tellurite glasses have demonstrated the presence of TeO₄ and TeO₃₊₁ or TeO₃ structural units. The thermal properties of this glass have been investigated from the study of DTA profile. The recorded optical absorption spectra of Pr³⁺: TZBL glass have shown eight absorption bands from 300 nm to 2,500 nm. The fluorescence emission has been observed mainly from ³P₁, ³P₀ and ¹D₂ states to the lower lying states and which are assigned to the transitions of ³P₀→ ³H_4,5,6; ³P₀→ ³F_2,3,4; ³P₁→³H₅ & ¹D₂→³H_4,5 upon excitations at three excitation states of ³P_0,1,2. From the time resolved spectra, it is found that ³P₀ level decays faster than ¹D₂ level. The fluorescence decay kinetics of ³P₀ and ¹D₂ levels have been measured and the lifetimes are found to be 21 and 39 μs, respectively.     

Characterization of TeO<Subscript>2</Subscript> based glass frits and morphology to their silver films

Novel Pb-free Ag paste with a TeO₂ based glass frit for front contact electrodes of crystalline silicon solar cells were prepared. The influence of TeO₂ content (44–80 mol%) on thermal properties, structure and chemical durability of TeO₂ based glass was investigated. The thermal expansion coefficient decreased firstly when the TeO₂ content reached 60 mol%, then increased with further increasing TeO₂ content. The glass transition temperatures are 400–450 °C and melting temperature was as low as 800 °C. The weight loss of Te-3 glass specimen value is 0.28?×?10^?3 mg/cm², improving the chemical durability of the TeO₂ based glass system. In addition, morphology of TeO₂ based Ag films sintering at various temperatures were also investigated. The grain size of the Ag film increased when the content of glass frit increased, and grain boundaries for sintering TeO₂ based Ag pastes was obvious. The host elements of Ag, Te, Bi, and O in AT-3 specimens were almost homogeneously distributed. The amounts of SiO₂ formed when the Ag films were firing at 750 °C, indicating the etching of SiN _x layer by TeO₂ based glass frit. The specific resistivity of silver conducting films with 3 and 5 wt% glass materials of silver component were 3.1 and 3.7 µΩ cm, respectively.