Effects of oxygen and carbon impurities on the optical transmission of As<Subscript>2</Subscript>Se<Subscript>3</Subscript> glass

The IR spectra of As₂Se₃ glass samples containing known amounts of oxygen (4 × 10^-3 to 7.7 × 10^-2 wt %) or carbon (5.8 × 10^-3 wt %) are measured, and the parameters of impurity-related absorption bands and extinction coefficients are determined. The effects of oxygen, carbon, sulfur, and hydrogen on the transmission of As₂Se₃ glass are analyzed. At an oxygen content on the order of 10^-5 wt %, this impurity causes optical losses in the range 900–1100 cm^-1 comparable to the intrinsic losses. The permissible carbon content of As₂Se₃ glass is 10^-6 to 10^-5 wt %. Carbon inclusions 0.07 µm in diameter cause optical losses comparable to the intrinsic losses in the spectral window of As₂Se₃ glass when present in a concentration of 10⁴ cm^-3.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 369–376.Original Russian Text Copyright © 2005 by Shiryaev, Smetanin, Ovchinnikov, Churbanov, Kryukova, Plotnichenko.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Oxide impurity absorptions in Ge-Se-Te glass fibres

Oxide impurity absorptions in Ge-Se-Te glass fibres and the cause of the absorption loss around 943 cm^–1, the frequency of the CO² laser, have been investigated. The oxygen in the glass bounds preferentially to germanium and causes the absorptions due to Ge-O bond vibrations at 765 cm^–1 (band I) and 1230cm^–1 (band II). The excess absorptions due to these bands were determined as 0.228cm^–1/P.p.m. wt O₂ for band-I and 0.006cm^–1 /p.p.m. wt O₂ for band II. The loss of the fibre at 943cm^–1 increased with the oxygen content. It was, however, revealed from the deconvolution of the IR spectra into the independent absorption components that the absorption tails of band I and band II did not affect the loss at 943 cm^–1. The content of the impurities except oxygen analysed by a mass spectroscopy was too low to affect the loss at 943 cm^–1.     

Ortho-para conversion in solid hydrogen,catalyzed by molecular oxygen impurities

Ortho-para conversion in solid hydrogen with small amounts of molecular oxygen as impurity (0.01–0.5%) was studied by NMR in the temperature range 4.2–7 K. The observed conversion rate was substantially greater than that of the natural conversion process in pure solid H₂ and revealed a strong dependence on temperature and the oxygen content in the sample. Obviously, the conversion is catalyzed by the large paramagnetic moments of O₂ impurities. Since the influence of O₂ is of very short range, the overall rate of the catalyzed conversion in the sample is determined by the relative diffusion of ortho-H₂ and the O₂ impurities. The diffusion coefficient was found to obey an Arrhenius behavior D(T)=3(2). 10^–11.exp[96(8)/T] cm²s^–1. This temperature dependence is interpreted in terms of vacancy-particle exchange by quantum tunneling through the intervening barrier.     

Oxidation kinetics of hot-pressed silicon carbide

The oxidation of silicon carbide, hot-pressed with 4 wt % Al₂O₃, in 1 atm dry oxygen follows classical parabolic behaviour with an activation energy of 481 kJ mol^–1 in the temperature range 1200 to 1400° C. The oxide film consists predominantly of cristobalite and a glassy phase in which additive (Al) and various impurity elements (Fe, Na, K, etc) concentrate. The desorption of CO(g) from the SiC/SiO₂ interface appears to be oxidation rate controlling.     

Structural,electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

A low cost chemical bath deposition (CBD) technique has been used for the preparation of Cu_2–xSe thin films on glass substrates. Structural, electrical and optical properties of these films were investigated. X-ray diffraction (XRD) study of the Cu_2–xSe films annealed at 523 K suggests a cubic structure with a lattice constant of 5.697 Å. Chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). It reveals that absorbed oxygen in the film decreases remarkably on annealing above 423 K. The Cu/Se ratio was observed to be the same in as-deposited and annealed films. Both as-deposited and annealed films show very low resistivity in the range of (0.04–0.15) × 10^–5 -m. Transmittance and Reflectance were found in the range of 5–50% and 2–20% respectively. Optical absorption of the films results from free carrier absorption in the near infrared region with absorption coefficient of 10⁸ m^–1. The band gap for direct transition, E_g.dir varies in the range of 2.0–2.3 eV and that for indirect transition E_g.indir is in the range of 1.25–1.5 eV.     

Solubility of AgCl and AgBr in HCl and HBr

The solubilities of AgCl and AgBr in aqueous HCl and HBr were determined between 298 and 368 K. The temperature-dependent solubility data were used to develop a method for purifying AgCl and AgBr by crystallization from solution. The impurity content of the resultant crystals was 10^–5to 10^–6wt %.     

Oxidation-reduction equilibria of vanadium in CaO-SiO2, CaO-Al2O3-SiO2 and CaO-MgO-SiO2 melts

A series of redox studies of vanadium have been carried out in CaO-SiO₂, CaO-MgO-SiO₂ and CaO-Al₂O₃-SiO₂ melts/slags equilibrated over oxygen partial pressures (pO₂) range 10^–2–10^–9 atm at 1600°C. V₂O₅ level was varied from 1–5 mol%. Three different melt basicities and alumina contents were investigated. Magnesia content was varied between 3.5 and 4.9 wt%. A newly developed analytical technique based upon electron paramagnetic resonance (EPR) spectroscopy was successfully applied to these melts. Two redox equilibria corresponding to V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ pairs followed the O-type redox reaction over the oxygen partial pressure range investigated. Higher oxidation states of vanadium were stabilized with increasing basicity of slags. Two redox pairs coexisted within oxygen pressure region 10^–4–10^–6 atm. However, redox ratios did not indicate clear trends with increasing V₂O₅ content in CaO-SiO₂-V₂O₅ system. In CaO-SiO₂-Al₂O₃-V₂O₅ slags, a slight increase in redox ratios (V³⁺/V⁴⁺) was obvious when alumina quantity was changed from 3.22 to 5.44% at a basicity ratio 1.3, indicating an increase in slag acidity. CaO-MgO-SiO₂-V₂O₅ slags showed a sharp decrease in redox ratios (V⁴⁺/V⁵⁺) between 10^–2–10^–6 atm with addition of 3.5 wt% MgO, due to increasing free oxygen ions in slags.     

Hot pressing and physical properties of Na beta alumina

Dense transparent/translucent Na-gb-alumina was hot pressed using commercial powders having low SiO₂ contents provided that agglomerates could be broken down by milling. Partial (up to 60 vol %) transformation to alpha alumina during hot pressing was caused by SiO₂ either present in some powders, or introduced by excessive milling or present through the addition of Na₂O-SiO₂ glass. Such transformation also results from increased storage time or from direct water contamination. Two wt % MgO was used to aid densification, and 2 wt % Na₂O to aid conductivity. Flexure strengths averaging 290 MN m^–2, a measured Young's modulus of 21.3×10⁴ MN m^–2, and the observed pores or flaws at the fracture origins gave calculated values for the fracture energy in good agreement with the directly measured value of 13 J m^–2, for larger pores and flaws. The ionic resistivity was low, e.g. 3 cm at 350° C. Effects of surface finish, limited porosity and hot pressing texture varied resistivity by up to a factor of 10.     

Gas permeability of poly(organophosphazenes)

The gas permeability and oxygen-to-nitrogen selectivity were determined for some poly-(organophosphazenes). It was found from the data that the membrane having the highest gas permeability was [NP(NHPrⁿ)(NEt₂)] _n , which had 1.5 x 10^–6cm³ (cm cm^–2) s^–1 (cm Hg)^–1 to oxygen or 2.2 x 10^–6cm³ (cm cm^–2) s^–1 (cm Hg)^–1 to nitrogen. On the other hand, the membrane having the highest oxygen-to-nitrogen selectivity of about 3 had the formula [NP(OC₆H₄Cl-p)₂] _n Also, the selectivity did not depend on the glass transition temperature of the membranes. The membrane prepared from [NP(OC₆H₄CH₃-p)2] _n had a negative activation energy for oxygen and nitrogen permeability.     

Laser Damage Threshold and UV Absorption of Doped Potassium Dihydrogen Phosphate Crystals

The effects of Pb, Ca, and Si impurities on the laser damage threshold and UV absorption of KH₂PO₄ crystals were studied. The laser damage threshold was found to be 6 × 10¹¹ W/cm² in crystals containing 5 × 10^–5 wt % and to decrease nonlinearly at higher impurity contents.     

Small polaron transport in V2O5–NiO–TeO2 glasses

Semiconducting glasses of the V₂O₅–NiO–TeO₂ system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 300–450 K were measured. The d.c. conductivities at 395 K for the present glasses were determined to be 10^–7 to 10^–1 S m^–1, indicating that the conductivity increased with increasing V₂O₅ concentration. A glass of composition 67.5V₂O₅–2.5NiO–30TeO₂ (mol %) having a conductivity of 2.47×10^–2 S m^–1 at a temperature of 395 K was found to be the most conductive glass among the vanadium-tellurite glasses. From the conductivity–temperature relation, it was found that a small polaron hopping model was applicable at the temperature above _D/2 (_D: the Debye temperature); the electrical conduction at T>_D/2 was due to adiabatic small polaron hopping of electrons between vanadium ions. The polaron bandwidth ranged from 0.06 to 0.21 eV. The hopping carrier mobility varied from 1.1×10^–7 to 5.48×10^–5 cm² V^–1 s^–1 at 400 K. The carrier density is evaluated to be 1.85×10¹⁹–5.50×10¹⁹ cm^–3. The conductivity of the present glasses was primarily determined by hopping carrier mobility. In the low-temperature (below _D/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.     

Microwave dielectric and elastic properties of glass-added Ba6−3xR8+2xTi18O54 (x = 2/3)

Microwave dielectric properties of Ba_6−3xSm_8+2xTi₁₈O₅₄ (x = 2/3) [BST] ceramics with the addition of 0–3 wt.% of various glasses have been studied. It has been found that the addition of 0.5 wt.% of the glasses decreases the sintering temperature by about 150 °C. In general, addition of 0.5 wt.% of Zn, Mg and Pb-based glasses deteriorate the quality factor, whereas aluminum and barium borosilicates do not decrease it considerably. The quality factor and dielectric constant decrease with increasing amount of glass. The temperature coefficient of resonant frequency shifts towards positive or negative depending on the composition of the glass. A glass–ceramic composite with a dielectric constant 64, Q × f nearly 8500 GHz and near to zero τ_f could be obtained at a sintering temperature of 1175 °C when 3–4 wt.% Al₂O₃–B₂O₃–SiO₂ glass was added to BST ceramic. The Young's modulus decreases with increasing amount of glass, irrespective of the composition of glass.     

An investigation of amorphous phase separation, leachability and surface area of an ionomer glass system and a sodium-boro-silicate glass system

Glasses from a complex SiO₂-Al₂O₃-P₂O₅-CaO-CaF₂ glass series, known as 'ionomer glasses' were investigated. For comparison, a sodium-boro-silicate (s-b-s) glass system, which is known to undergo amorphous phase separation was also investigated. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and BET surface area and pore distribution analysis were the principal analytical techniques used in this study. SEM analysis of the ionomer glass compositions revealed smooth spherical droplets of 2–15 nm while the background morphology appeared rough and speckled. A classic interconnected structure was observed for the s-b-s glass. EDX analysis of the s-b-s glass confirmed that the sodium-borate phase was removed by leaching with 0.3 M HNO₃, leaving behind a silica-rich structure. EDX analysis of ionomer glasses leached with 10% NaOH showed that the calcium and phosphate phases were being removed, although not to completion. For the base s-b-s glass a surface area of m 8² g^–1 was recorded. However, the base glass after extraction with 0.3 M HNO₃ of the sodium borate rich phase gave a BET surface area of 330 m² g^–1 indicating that it had already undergone phase separation on quenching from the melt, giving rise to a fine scale interconnected structure. The leached s-b-s glasses exhibited type 4 adsorption/desorption isotherms characteristic of mesoporous materials. Glasses which had been heat treated at 580°C for 4 h exhibited a surface area of 62 m² g^–1. This indicates that the as-quenched glass is already phase separated and that the phase separated microstructure is coarsening on heat treatment. A surface area of 4 m² g^–1 was measured for the base ionomer glasses. After leaching with 10% NaOH this value rose 10-fold with a maximum surface area of 44.1 m² g^–1 being recorded. The ionomer glasses also exhibited adsorption/desorption isotherms characteristic of mesoporous materials.     

Effect of oxygen on sintering of AlN

The effect of the oxygen impurity on the densification behaviour of AlN was investigated. AlN powders containing different amounts of oxygen were synthesized from alumina and hot-pressed. The way in which oxygen accelerates densification is remarkable. Contrary to what is expected from the densification equation, the sintering rate decreases during the holding time at temperatures above 1900° C. This discrepancy is caused by the liberation of oxygen during the hot-pressing. The compression test, conducted on the hot-pressed specimens, shows that oxygen impurity also improves the mechanical strength of sintered AlN. The sintered specimens with more than 2.5 wt % of oxygen have compressive fracture stresses above 150kg mm^–2, which are adequate for a refractory material.     

Non-stoichiometric disorder in α-Nb2O5 at elevated temperatures

The electrical conductivity of polycrystalline-Nb₂O₅ was determined for the oxygen partial pressure range of 10⁰ to 10^–20 atm and temperature range 700 to 1150 ° C. The data were found to be proportional to the –1/6th power of the oxygen partial pressure for the oxygen pressure range 10^–20 to 10^–9 atm, and proportional toPO ₂ ^–1/4 for oxygen pressures greater than 10^–9 atm. The region of linearity where electrical conductivity varies as the –1/4th power of increased as the temperature was decreased. Thermogravimetric measurements were carried out in the temperature range 950 to 1250 ° C. The deviation from stoichiometry in-Nb₂O₅ (x in Nb₂O_5–x ) as a function of partial pressure of oxygen showed two distinct regions, namely a region with an approximately –1/6th dependence on and a region where the deviation was nearly independent of oxygen partial pressure. The electrical conductivity and thermogravimetric data are consistent with the presence of small amounts of acceptor impurities in-Nb₂O₅.     

Preparation and studies on surface modifications of calcium-silico-phosphate ferrimagnetic glass-ceramics in simulated body fluid

The structure and magnetic behaviour of 34SiO₂–(45 − x) CaO–16P₂O₅–4.5 MgO–0.5 CaF₂ − x Fe₂O₃ (where x = 5, 10, 15, 20 wt.%) glasses have been investigated. Ferrimagnetic glass-ceramics are prepared by melt quench followed by controlled crystallization. The surface modification and dissolution behaviour of these glass-ceramics in simulated body fluid (SBF) have also been studied. Phase formation and magnetic behaviour have been studied using XRD and SQUID magnetometer. The room temperature Mössbauer study has been done to monitor the local environment around Fe cations and valence state of Fe ions. X-ray photoelectron spectroscopy (XPS) was used to study the surface modification in glass-ceramics when immersed in simulated body fluid. Formation of bioactive layer in SBF has been ascertained using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The SBF solutions were analyzed using an absorption spectrophotometer. The magnetic measurements indicated that all these glasses possess paramagnetic character and the [Fe²⁺/Fe³⁺] ions ratio depends on the composition of glass and varied with Fe₂O₃ concentration in glass matrix. In glass-ceramics saturation magnetization increases with increase in amount of Fe₂O₃. The nanostructure of hematite and magnetite is formed in the glass-ceramics with 15 and 20 wt.% Fe₂O₃, which is responsible for the magnetic property of these glass-ceramics. Introduction of Fe₂O₃ induces several modifications at the glass-ceramics surface when immersed in SBF solution and thereby affecting the surface dissolution and the formation of the bioactive layer.     

Influence of the non-bridging oxygen groups on the bioactivity of silicate glasses

The effect of the composition and bonding configuration of the bioactive silica-based glasses on the initial stage in vitro bioactivity is presented. Information of the IR active Si–O groups of glass in the system SiO₂–P₂O₅–CaO–Na₂O–K₂O–MgO–B₂O₃ was obtained by fourier transform Infrared (FTIR) spectroscopy. Two different bands associated to non-bridging oxygen stretching vibrations (Si–O–1NBO and Si–O–2NBO) and a gradual shifting of the bridging oxygen stretching vibration (Si–O) have been observed and evaluated. Both effects are attributed to a decrease of the local symmetry originating from the incorporation of alkali ions into the vitreous silica network. The Si–O–NBO(s)/Si–O(s) absorbance intensity ratio increases with a gradual incorporation of the alkali ions (diminution of SiO₂ content) following a linear dependence up to values close to 50 wt % of SiO₂. In vitro test analysis by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) showed a correlation between the amount and type of the non-bridging oxygen functional groups and the growth of the silica-rich and CaP layers. It was found that a minimum concentration of Si–O–NBO bonds in the glass network is required in order to have an efficient ion exchange and dissolution of the silica network. Finally, the bioactivity of the glass is favored by the presence of the Si–O–2NBO groups in the glassy network. The role of these functional groups in the dissolution of the silica network through the formation of silanol groups and the adsorption of water is discussed.     

Optical absorption spectra studies for amorphous Cu2O-Bi2O3 glass system

Infrared absorption spectra were measured in the spectral range 4000–200 cm^–1 for the Cu₂O-Bi₂O₃ glass system. Strong bands were observed around 436–477, 600–632, 700–715, 810–875, 975–1000, 1550–1610 and 3225–3510 cm^–1 which are due to harmonics of the Bi-O-Bi stretching vibration, Cu-O stretching vibrations, O-Bi-O stretching vibrations, O-Bi-O bending vibrations, Bi-O stretching vibrations, free H₂O normal-mode bending vibrations and free H₂O molecules or OH^– ions, respectively. Quantitative justification of these absorption bands shows that the values of the experimental wave number for most recorded absorption bands agree well with the theoretical ones.The optical absorption spectra were recorded for the same glass system in the spectral range 300–700 Nm. These records show that the absorption edge has a tail extending towards lower energies. The edge shifts towards lower energies with increasing Cu₂O content. This shift is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. By increasing the Cu₂O content, the optical energy gap decreases, while the width of the localized states increases.     

Diffusion of tin (IV) in silicate glazes and glasses

The diffusion coefficients of Sn(IV) in an aluminosilicate glass and a commercial glaze have been measured from 809 to 1505° C. Two experimental techniques have been used. In one method, single crystals of SnO₂ were embedded in either the powdered glass or sealed into a bar of the glass. After the diffusion anneal, the Sn(IV) concentration profile was determined by EPMA. In the other method, radioactive ¹¹³Sn was used as a tracer and the profile determined by measuring the X-ray emission. The results gave a good agreement between the two methods. The diffusion coefficients in the glaze ranged from 7×10^–20 m² sec^–1 at 809° C to 1.9×10^–14 m² sec^–1 at 1250° C and in the glass, from 5.6×10^–15 m² sec^–1 at 1307° C to 1.6×10^–11 m² sec^–1 at 1505° C.     

Study of fluorine losses and spectroscopic properties of Er doped oxyfluoride silicate glasses and glass ceramics

The fluorine losses during synthesis of Er³⁺ doped transparent glasses in the SiO₂–PbO–PbF₂ system were investigated. The final fluorine contents of the glasses were detected by using a fluorine ion selective electrode. The results show that high fluorine losses are occured in the normal preparation processes. With the increase of initial PbF₂ contents or melting time resulted in the increase of the fluorine losses. The thermal and spectroscopic properties of the glasses and the corresponding glass ceramics were investigated through the analysis of the differential scanning calorimetry (DSC), absorption and upconversion luminescence spectra. The effects of fluorine contents show a decrease of the glass transition temperatures (Tg) of the glasses and an enhancement of upconversion intensity of the corresponding glass ceramics.