Ultraviolet absorption of cerium(III) and cerium(IV) in some simple glasses

The optical absorption spectra of cerium (III) and cerium (IV) in Na₂O-B₂O₃, Na₂O-SiO₂, Na₂O-P₂O₅ glasses, and in H₂O-H₂SO₄ and H₂O-H₃PO₄ solutions have been studied. Individual molar extinction coefficients of cerium (III) and cerium (IV) at different wavelengths (350 to 200 nm) have been estimated. In all the glasses and solutions, cerium (IV) produces a very strong and broad charge transfer band around 250 nm; the intensity, half-width, and position of this band change appreciably with glass composition. Cerium (III) in glass and in aqueous solution produces a number of absorption bands in the ultraviolet region corresponding to the f → d transitions. The cerium (III) bands are sharp and well resolved in Na₂O-P₂O₅ and in low-alkali borate glasses; the sharpness of resolution deteriorates in Na₂O-SiO₂, and in high-alkali borate glasses. The intensity of cerium (III) absorption also changes with glass composition. In all the glasses the molar extinction coefficient of cerium (IV) is 5 to 10 times stronger than that of cerium (III).     

Optical properties of oxide glasses containing transition metals: Case of titanium- and chromium-containing glasses

One of the major driving forces for the development of new glasses is the demand for high optical non-linearity with reduced cost and a higher damage resistance. Oxide glasses with large non-linear refractive index and non-linear absorption coefficient are promising materials for fiber telecommunication and for non-linear optical devices such as ultrafast optical switches, power limiters, real time holography, self-focusing, white-light continuum generation and photonic applications. To get insight into the optical absorption in amorphous materials, studies are still needed for revealing the nature of photoelectronic excitations in these materials by comparison with that in crystals which have been understood firmly based on band theory. Although the IR absorption loss in oxide glasses is larger than of fluorides, low light scattering loss is expected in these oxide glasses because they have lower glass transition temperature. In addition, small concentration of dopant such as alkaline metal and alkaline earth metal elements gives rise to the structural relaxation of the frozen-in density fluctuations even below glass transition temperature T_g, adding to the reduction of T_g as well. A review of the fundamentals and recent research advances in optical properties of oxide glasses containing chromium or titanium is presented.     

Characteristics of CeOx–VO2 composite thin films synthesized by sol–gel process

Pure vanadium dioxide (VO₂) and CeOx–VO₂ (1.5 < x < 2) composite thin films were grown on muscovite substrate by inorganic sol–gel process using vanadium pentaoxide and cerium(III) nitrate hexahydrate powder as precursor. The crystalline structure, morphology and phase transition properties of the thin films were systematically investigated by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, FE-SEM and optical transmission measurements. High quality of the VO₂ and CeOx–VO₂ composite films were obtained, in which the relative fractions of +4 valence state vanadium were above 70 % though the concentrations of cerium reached 9.77 at %. However, much of cerium compounds were formed at the edge of grains and the addition of cerium resulted in more clearly defined grain boundaries as shown in SEM images. Meanwhile, the composite films exhibited excellent phase transition properties and the infrared transmittance decreased from about 70 to 10 % at λ = 4 μm bellow and above the metal–insulator phase transition temperature. The metal–insulator phase transition temperatures were quite similar with about 66 °C of the pure VO₂ and CeOx–VO₂ composite thin films. But hysteresis widths increased with more addition of cerium, due to the limiting effect of grain boundaries on the propagation of the phase transition. Particularly, the CeOx–VO₂ composite film with an addition of 7.82 at % Ce showed a largest hysteresis width with about 20.6 °C. In addition, the thermochromic performance of visible transmittance did not change obviously with more addition of cerium.     

Some effects of the addition of iron oxide and of annealing on the optical and infrared absorption spectra of sodium tetraborate glasses

The optical and infrared absorption spectra of sodium tetraborate glasses containing iron oxide have been studied as a function of iron content. It was found that the addition of iron oxide shifts the optical absorption edges towards lower energies and introduces a new absorption band as compared with the optical absorption spectrum of pure sodium tetraborate glass. The addition of iron does not introduce any new absorption band in the infrared spectrum of pure sodium tetraborate glass. The measurements were made on unannealed samples and samples annealed at different temperatures.     

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.     

Annealing dependence of optical properties of Ga20S75Sb5 and Ga20S40Sb40 thin films

Amorphous Ga₂₀S₇₅Sb₅ and Ga₂₀S₄₀Sb₄₀ thin films were prepared onto glass substrates by using thermal evaporation method. The effect of annealing (under vacuum) at different temperatures on the optical parameters was investigated in the temperature range 373-593 K. The optical absorption coefficient (α) for the as-deposited and annealed films were calculated from the reflectance and transmittance measurements in the range 190-900 nm. X-Ray diffraction indicates that the as-deposited films and those annealed up to the glass transition temperature (T_g) exhibit amorphous state. On annealing above the glass transition temperature these films show a polycrystalline structure. Analysis of the optical absorption data indicates that the optical band gap E_g^opt of these films obeys Tauc's relation for the allowed non-direct transition. It was found that the optical band gap E_g^opt increases with annealing temperature up to T_g, whereas above T_g there is a remarkable decrease. The obtained results were interpreted on the basis of amorphous- crystalline transformation.     

Effect of NiO content on the optical band gap, refractive index, and density of TeO2–V2O5–NiO glasses

Amorphous layers and bulk glasses of 40TeO₂–(60 ? x)V₂O₅–xNiO compositions with 0 ≤ x ≤ 30 (in mol%) have been prepared using the usual blowing technique and press-melt quenching method, respectively. The optical absorption spectra of the layers have been recorded in the wavelength range 400–800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The optical band gap, width of the tail of the localized states, and refractive index have been evaluated using available theories. Results show that the values of optical band gap decrease from 2.02 to 1.64 eV as the contribution of NiO increases. The refractive index dispersion is fitted to the single oscillator model, and results show that the static refractive index increase from 1.309 to 1.673 as the NiO content increases. The glass transition temperature, density, and molar volume have been studied, indicating act of NiO as network modifier. Values of theoretical optical basicity are also reported.     

Characterization of ZBGAN glasses

The physical and electrical properties of a ZrF₄-BaF₂-GdF₃-AIF₃-NaF (ZBGAN) glass have been studied. The addition of NaF increases the glass-forming ability of the base composition glass yet does not degrade the optical characteristics. The viscosity decreased with increasing NaF, suggesting that the increased glass-forming ability was due to the confusion principle. The electrical conductivity decreased with increasing NaF for low temperatures but increased at higher temperatures. The activation energy showed an increase with increasing NaF. The data suggest that the conductivity is not due to the total fluorine ion concentration.     

Effects of annealing temperatures on optical and electrical properties of vacuum evaporated Ga15Se77In8 chalcogenide thin films

The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary parts of dielectric constants) of amorphous and thermally annealed thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses with thickness 4000 Å have been investigated from absorption and reflection spectra as a function of photon energy in the wave length region 400-800 nm. Thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses were thermally annealed for 2 h at three different annealing temperatures 333 K, 348 K and 363 K, which are in between the glass transition and crystallization temperature of Ga₁₅Se₇₇In₈ glasses. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It was found that the optical band gap decreases with increasing annealing temperature. It has been observed that the value of absorption coefficient and extinction coefficient increases while the values of refractive index decrease with increasing annealing temperature. The decrease in optical band gap is explained on the basis of the change in nature of films, from amorphous to crystalline state. The dc conductivity of amorphous and thermally annealed thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses is also reported for the temperature range 298-393 K. It has been observed that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The dc conductivity was observed to increase with the corresponding decrease in activation energy on increasing annealing temperature in the present system. These results were analyzed in terms of the Davis-Mott model.     

Thermal and optical properties of zinc halotellurite glasses

Zinc halotellurite glasses were studied with respect to the glass transition, softening temperature, thermal expansion, optical energy gap, Urbach energy, density, molar volume, refractive index, polarizability, molar refraction and third order non-linear optical susceptibility. Thermal characteristic were determined using a dilatometry. The optical absorption in the wavelength range (300–3200 nm) was measured. From the absorption edge studies, the values of optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. Optical parameters viz., color dispersion, dispersion energy, E _d, average oscillator energy, E ₀, and third order non-linear optical susceptibility values are estimated from measuring the refractive index at different wavelength. Results obtained are discussed in terms of the glass structure.     

EPR and optical absorption studies of Cr3+ ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cr³⁺ ions in Calcium alumino borate (CaAB) glasses have been studied. The EPR spectra exhibit weak resonance signal at g ≈ 4.50 and intense resonance signal at g ≈ 1.98. A sharp resonance signal at g ≈ 1.97 was also observed at lower concentrations of chromium. The concentration dependence of the linewidth of the resonance signal at g ≈ 1.98 suggests the formation of Cr³⁺ ion clusters by magnetic superexchange interactions. The temperature dependence of the peak to peak intensity and the linewidth of the resonance signal at g ≈ 1.98 suggests that the exchange interactions between Cr³⁺ ions in the present sample were antiferromagnetic in nature with Néel temperature, T _N = 233 K. From the number of spins participating in the resonance at g ≈ 1.98, the paramagnetic susceptibility (χ) was calculated at different temperatures (233–295 K). A plot of 1/χ and T was found to obey Curie-Weiss law with negative Curie temperature. By measuring the relative intensities of the resonance signal at g ≈ 1.98, at different temperatures, the value of antiferromagnetic coupling constant (J) has been estimated. The optical absorption spectrum of chromium doped CaAB glass exhibits four bands, characteristic of Cr³⁺ ions, in nearly octahedral symmetry. From the band positions, the crystal field splitting parameter, Dq and the Racah interelectronic repulsion parameters, B and C were evaluated. The optical band gap (E_opt) and the Urbach energy (ΔE) were calculated from the ultraviolet absorption edges.     

Local structure,glass transition,structural relaxation,and crystallization of functional oxide glasses investigated by Mössbauer spectroscopy and DTA

This review paper summarizes early Mössbauer and DTA studies of different oxide glasses containing small amounts of iron (III) or tin (IV) as the probe. A lot of valuable information of the atomic level has been obtained about the role of nonbridging oxygen (NBO), network former (NWF), network modifier (NWM), local network structure, glass transition, structural relaxation, crystallization, etc. Introduction of alkali oxide into iron (III)-containing oxide glass causes a marked decrease in glass transition temperature (T_g) amounting to 100 °C and a concordant decrease in quadrupole splitting (Δ) of Fe^III, which reflects decreased distortion of NWF–oxygen polyhedra and formation of NBO. By contrast, introduction of non-alkali oxide into oxide glass causes an increase in T_g amounting to more than 100 °C and a concordant increase in Δ, reflecting increased distortion of NWF–oxygen polyhedra in highly cross-linked network. These experimental results led to a discovery of “T_g-Δ rule”, which was consistent with the “conformer model” proposed for polymers by Matsuoka and Quan. Debye temperatures (θ_D) obtained by low-temperature Mössbauer measurements proved to be useful to determine short- and long-range structures of glass and glass ceramics. Isothermal annealing of vanadate glasses at temperatures higher than T_g or crystallization temperature (T_c) causes a “tunable” decrease in DC-resistivity from the order of MΩ cm to Ω cm. Introduction of metal oxide with a narrow bandgap (E_g) is highly effective to increase the conductivity after the annealing. It was proved that “structural relaxation” of NWF–oxygen polyhedra and resultant decrease in the activation energy (E_a) for conduction are responsible for the improved conductivity. Heat treatment of IR-transmitting aluminate, gallate, and tellurite glasses at temperatures higher than T_g or T_c revealed that crystallization was triggered by the cleavage of NWF–oxygen bonds. These findings will contribute to the development of functional glass and glass ceramics such as smart glass and eco-friendly glass.

     

Glass formation domains and structural properties of nonconventional transition metal ion glasses

Glass formation domains and structural properties of some binary transition metal ion glasses based on nonconventional network formers Bi₂O₃ and PbO have been investigated. With the same network former, the glass formation domains depend on the transition metal ions. Homogeneous glasses with random network structure were obtained, as evidenced by the composition dependent density, molar volume and glass transition temperatures. Significant information about possible structural units in these glasses has been obtained from the IR spectra of these glasses.     

Studies of radiation defects in cerium,europium and terbium activated oxyfluoride glasses and glass ceramics

Terbium, cerium and europium activated oxyfluoride glasses and glass ceramics have been studied by thermally stimulated luminescence (TSL) and optical absorption techniques after the X-ray irradiation. A creation of colour centres in oxyfluoride glass matrix and TSL peaks depending on the activator type were observed. LaF₃ and rare earth activators were analysed by SEM–EDS.     

Zinc vacancy mediated structural phase transition and photoluminescence in nanocrystalline ZnS thin films

Nanocrystalline thin films of zinc sulphide were prepared on glass substrate at various deposition temperatures by thermal evaporation technique. The variation of the structural and optical properties of films deposited at various substrate temperatures was investigated in detailed. X-ray diffraction spectra showed that films deposited at 300 and 400 °C are polycrystalline in nature having cubic and both cubic and wurtzite structure, respectively. However, film deposited at temperature of 200 °C was found to be amorphous in nature. The ultra-violet and visible absorption studies showed that the band gap of films increases with increase in deposition temperatures. Photoluminescence spectra displayed emission near 396 and 444 nm, which arises due to zinc vacancies and sulphur vacancies, respectively and has been correlated to phase transition of the films.     

Some optical properties of Se-Ge-As amorphous chalcogenide glasses

The effects of composition, film thickness, substrate temperature, and annealing of amorphous thin films of Se₇₅Ge_25−x As _x (5⩽x⩽20) on their optical properties have been investigated. X-ray diffraction revealed the formation of amorphous films. The absorbance and transmission of vacuum-evaporated thin films were used to determine the band gap and refractive index. Optical absorption measurements showed that the fundamental absorption edge is a function of glass composition and the optical absorption is due to indirect transition. The energy gap increases linearly with increasing arsenic content. The optical band gap,E _opt, was found to be almost thickness independent. The shapes of the absorption edge of annealed samples displayed roughly the same characteristic as those of the unannealed films, but were shifted towards shorter wavelengths; as a result,E _opt increased andE _e, the width of the band tails, decreases. The increase inE _opt is believed to be associated with void removal and microstructural re-arrangement during annealing. The influence of substrate temperature on the optical parameters is discussed.     

Effect of heat treatment on fracture behavior of steel-wire-reinforced gray cast iron

In this experimental study, fracture toughness of heat-treated metal matrix composite was investigated. The gray cast iron was reinforced with steel wire of volume fraction of V_r = 0.05 and three-point bend specimens were manufactured to determine fracture toughness. Heat treatment was applied to the specimens at the normalization temperatures of 850°C and then cooled in three distinct environments (water, air, and furnace). Fracture toughness of the metal matrix composite was calculated by unloading compliance method. The study shows that the fracture toughness of the steel-wire-reinforced gray cast iron increases with the increase in cooling rate. Scanning electron microcopy (SEM) analyses were used to examine the microstructure and fracture surface. It is observed that the carbon diffuses from the gray cast iron to the steel wire and transition region having partially dissolved graphite was observed due to carbon diffusion, and it plays an important role in the fracture toughness depending on the cooling media.     

Effect of chromium content on electrical resistivity and tensile properties of Ti–Fe–Cr alloys

Abstract

The effects of substituting chromium for iron and the use of low cost ferrochromium alloys in the production of β-Ti–Fe–Cr alloys have been studied with respect to phase constitution, stability, and mechanical properties, in solution treated and quenched states using resistivity, hardness measurement, X-ray diffraction, and tensile testing. Resistivity at room and liquid nitrogen temperatures, and hardness decreased while the ratio of resistivity at liquid nitrogen temperature to that at room temperature increased with increases in chromium content. Alloys of Ti–Fe–Cr, with almost the same electron per atom value, with higher chromium content have smaller volume fractions of athermal omega than alloys with higher iron content. There is less solution hardening in the former alloys than in the latter alloys. Tensile strength decreased with increases in chromium content, while elongation and reduction in area significantly increased. The balance between tensile strength and ductility (elongation and reduction in area) improved in the alloys with added chromium as a substitute for iron. Therefore, no negative influences of ferrochromium alloying on mechanical properties was observed in this study.     

EPR and optical absorption studies of Cu ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu²⁺ ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu²⁺ ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures (T) and from the 1/χ-T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the ²B_1g → ²B_2g transition of the Cu²⁺ ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane σ bonding between Cu²⁺ ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap (E_opt) and the Urbach energy (ΔE) are evaluated. The variation in E_opt and ΔE is explained based on the number of defect centers in the glass.     

MoO3 and Sb2O3 effects on bubble formation in silicate glass coatings during sintering

Small additions (0.25–0.5 mol%) of MoO₃ were effective in preventing bubble defects from forming in silicate glass powder coatings during sintering, without changing the glass transition temperature or molten viscosity. Surface tension was reduced to a similar linear degree as predicted by Kucuk's model, by approximately 20 mN/m per mol% MoO₃. MoO₃ increases the temperature where open porosity is sealed in the coating, allowing gas to escape before bubbles form. Sb₂O₃, a common fining agent used in industrial glass melts, does not significantly affect surface tension but produced higher bubble size and volume due to reduction above 1050 °C. Bonded OH groups in the glass frit were identified as a source of gas for bubble growth.