Spectroscopic and electrical studies of sodium tetraborate glasses containing nickel oxide

The infrared spectra. X-ray diffraction and electrical conductivity of sodium tetraborate glasses containing nickel have been studied as a function of nickel oxide content. It was found that addition of nickel oxide does not seem to introduce any new absorption band as compared with the infrared spectrum of pure sodium tetraborate glass. The electrical conductivity measurements revealed that the activation energy for conductivity increases with nickel oxide content. This could be explained on the basis of the concept of Hubbard bands, and possibly by a block effect of the nickel ion on the overall mobility of the sodium ion. Measurements were made on unannealed samples and some samples annealed at different temperatures. Annealing the samples at temperatures in the range 460 to 480° C causes the appearance of a crystalline phase, resulting in an increase of electronic conductivity.     

Optical,infrared and DSC studies of sodium tetraborate glasses containing copper oxide

The optical absorption, density, DSC and infrared absorption spectra of a series of sodium tetraborate glasses are measured as a function of copper content up to 5 mol%. It is found that the addition of CuO shifts the fundamental absorption edges towards lower energies in the range from 6.17–3.48 eV. The addition of CuO does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium tetraborate glass. DSC measurements showed endothermal peaks varying from 486–476 °C depending on the CuO content.     

Some effects of the addition of nickel oxide and of annealing on the optical absorption of sodium tetraborate glasses

A range of sodium tetraborate glasses containing nickel oxide was prepared and the optical absorption spectra measured. The differential scanning calorimetry technique was used to study compositional features of the glass formation. It was found that the addition of nickel oxide decreases the optical energy gap and introduces new absorption bands as compared with the optical absorption spectrum of pure sodium tetraborate glass. The results revealed that the decrease in the optical energy gap and the disappearance of some absorption bands of the annealed samples could be attributed to an increase in the concentration of reduced valence states of nickel ions which accompanies the microstructure formation.     

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.     

Studies of RbF-BeF2 glasses by differential scanning calorimetry

The heat capacity, softening temperature, and crystallization temperature of RbF-BeF₂ (10, 15, 18, 22, and 27 mol % RbF) glasses were measured by differential scanning calorimetry. The results lend support to the view that RbF-BeF₂ glasses are diphasic. The glasses studied are shown to contain fragments of (BeF₃) _n ^-n fluoroberyllate chains and to be close in many aspects to KF-BeF₂ glasses.     

A spectroscopic study of some sodium tetraborate glasses containing lead and copper

Optical absorption, infra-red absorption spectra and differential scanning calorimetry of amorphous (Na₂B₄O₇)₈₀-(Pb₃O₄)_20-x -(CuO) _x systems were studied as functions of copper content up to 10 mol%. When the Pb₃O₄ in the glasses is gradually replaced by CuO, a pronounced decrease in the optical energy gap and an increase in the optical absorption at 750 nm due to the CU²⁺ ions is observed. The change in the optical absorption may be attributed to the concentration variation of the Cu²⁺ ions in the glasses as a consequence of changing the lead content.     

Temperature-modulated differential scanning calorimetry studies of the structure of bulk and film GexAsyS60 chalcogenide glasses

The recent novel temperature-modulated differential scanning calorimetry (TA Instruments MDSCTM) technique has been applied to the measurement of thermal properties of GexAsyS60 chalcogenide glasses in the glass transition region in bulk glasses and in their thin films. The reversing and non-reversing heat flows through the glass transformation region during both heating and cooling schedules were measured and the values of the parameters, Tg, ΔH, Cp and ΔCp, which characterize the thermal events in the glass transition region, were determined. The structurally determined parameters, Tg, ΔH, Cp and ΔCp, reveal significant changes with composition because in the GexAsyS60 glasses the average coordination number, 〈r〉, increases from 2.4 to 2.8 with increasing x from 0 to 40 at% Ge. A maximum in Tg, ΔH and Cp and a minimum in the heat capacity change, ΔCp, at Tg occur near the composition for which x≈30 at% Ge. These extrema which appear in both films and bulk glasses are ascribed to a change in the network function of Ge atoms replacing As atoms in a covalent network. Recent structural models for chalcogenide glasses have been considered to explain the observed thermal properties. This revised version was published online in November 2006 with corrections to the Cover Date.     

Studies of LiF-BeF2 and KF-BeF2 glasses by differential scanning calorimetry

The heat capacity, softening temperature, and crystallization temperature of BeF₂, LiF-BeF₂ (4, 7, 7.5, 9, and 10 mol % LiF), and KF-BeF₂ (6.5, 12, 17, and 27 mol % KF) glasses were determined by differential scanning calorimetry. For BeF₂, the softening temperature was measured as a function of the heating rate. The results are interpreted in terms of glass structure.     

Some studies of the optical properties of copper phosphate glasses containing praseodymium

A range of copper phosphate glasses containing praseodymium was prepared and the optical absorption edges and infrared optical absorption spectra were measured. The optical energy gap of copper phosphate glass doped with praseodymium is slightly higher than the corresponding composition of the base glass. Heat treatment at 400 and 800° C caused some changes in the infrared absorption bands which are related to the characteristics of the Pr₆O₁₁₁ component.     

Hydrogen trapping in metallic glasses investigated by positron annihilation and differential scanning calorimetry

Positron annihilation experiments have been performed on the metallic glasses Co₅₈Ni₁₀Fe₅ B₁₆Si₁₁, Fe₇₈B₁₃Si₉ and Fe₈₁B_13.5Si_3.5C₂ produced by melt-spinning. For the metallic glass Co₅₈Ni₁₀Fe₅B₁₆Si₁₁ it has been found that the positron lifetime spectrum is either single-component or resolvable in two exponential terms, depending on the production parameters of the ribbons. The commercial metallic glass Fe₇₈B₁₃Si₉ (2605S2) shows a two-component spectrum while the alloy Fe₈₁ B_13.5Si_3.5C₂ (2605SC) exhibits a single-component spectrum. After hydrogen charging no significant changes are observed in the positron lifetime of those metallic glasses which exhibit a single-component spectrum. For ribbons showing a two-term spectrum, the intensity of the long-lived component_{l 2} decreases with the cumulative charging time. This decrease is interpreted in terms of hydrogen trapping in the structural defects responsible for the long-lived component. Differential scanning calorimetry of ribbons of Co₅₈Ni₁₀Fe₅B₁₆Si₁₁ suggest that hydrogen in extended structural defects should induce some local structural change.     

Nanocrystallization of ferroelectric strontium bismuth vanadium niobate in lithium tetraborate glasses

Transparent glass samples in (100-3x) (Li2O-2B2O3)-x(SrO-Bi2O3-0.7Nb2O5-0.3V2O5) (10 < or = x < or = 60, in molar ratio) system have been fabricated via conventional melt-quenching technique. The as-quenched samples, of all the compositions under study have been confirmed to be amorphous, by X-ray powder diffraction (XRD) studies. Differential thermal analysis (DTA) was employed to confirm the glassy nature of the as-quenched glasses. Glass composites comprising vanadium doped strontium bismuth niobate nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. Perovskite SrBi2(Nb0.7VO3)2O9-delta phase formation was found to be preceded by an intermediate fluorite phase which was established via XRD and transmission electron microscopy (TEM). The dielectric constants (epsilonr) of the as-quenched glasses as well as the glass nanocrystal composites decreased with increase in frequency (100 Hz-10 kHz) at 300 K. Interestingly, the dielectric constant of the glass nanocrystal composite (heat-treated at 783 K/6 h) undergoes a maximum in the vicinity of the crystallization temperature of the host glass (Li2B4O7) reaching an anomalously high value (approximately 10(6)) at 800 K. Different dielectric mixture formulae were employed to rationalize the dielectric properties of the glass nanocrystal composite. The optical transmission properties of these glass nanocrystal composites were found to have strong compositional dependence.     

Some optical properties of germania glasses containing praseodymium and chlorine

A range of germanate glasses containing praseodymium and chlorine was prepared. The optical absorption edges and infrared absorption spectra were measured. It is found that a small addition of PrCl₃ to GeO₂ glasses decreases the optical energy gap, but further addition of PrCl₃ increases the optical energy gap. The main infrared absorption bands in the GeO₂-PrCl₃ glasses are related to those characteristic of the GeO₂ component.     

Structure and physical properties of sodium borate glasses containing nickel oxide

A series of glass samples were prepared from a mixtures of B₂O₃, Na₂O and NiO. The role of nickel oxide in a glass matrix was studied by using infrared spectra, optical absorption, magnetic susceptibility, density, and differential thermal analysis (DTA). It was shown that the addition of nickel oxide at different concentrations to the glass batches causes some deformation in the glass structure. The values of ligand field strength and Racah parameter indicated an increasing degree of covalency. The glass samples exhibited diamagnetic behaviour with NiO content up to 1 g, then paramagnetic behaviour. The densities and glass transition temperatures decreased with increase in the NiO content up to 0.2 g and then increased again. This tendency may be related to changes in the glass structure.     

Polarised infrared and differential scanning calorimetry studies on oriented vinyl pipe materials

The molecular orientation in a conventionally extruded PVC pipe, a uniaxially oriented PVC pipe and a biaxially oriented PVC pipe has been studied via Infrared dichroism. The degree of order or crystallinity has also been studied by Differential Scanning Calorimetry and also via Infrared Spectroscopy. The fundamental structural difference between the conventional and oriented pipes was that polymer chains were preferentially aligning in the hoop direction for oriented pipes whereas they were fairly isotropic in the conventional pipe with a slight preferential alignment in the axial direction. Analysis of the C–Cl stretching mode indicated that the uniaxially oriented pipe had much higher alignment of the C–Cl bond in the axial direction than the biaxial pipe, which correlates with higher fracture toughness for circumferential cracking in the biaxial pipe. Both DSC and Infrared spectroscopy detected little change in the crystallinity or order in the oriented pipes compared to the conventionally extruded pipes.     

Synthesis,EPR and optical spectroscopy of the Cr-doped tetraborate glasses

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence spectra as well as luminescence kinetics of the Li₂B₄O₇:Cr and KLiB₄O₇:Cr tetraborate glasses were investigated at T = 300 K. The Li₂B₄O₇:Cr and KLiB₄O₇:Cr glasses containing 0.4 and 1.6 mol.% Cr₂O₃ of high optical quality were obtained from polycrystalline compounds by fast cooling of the melts. The X-band EPR spectroscopy shows that the Cr impurity is incorporated in the tetraborate glass network as isolated Cr³⁺ centers and Cr³⁺–Cr³⁺ pairs coupled by magnetic dipolar and exchange interactions. The EPR spectral parameters (g_eff and ΔB_pp) of both Cr³⁺ and Cr³⁺–Cr³⁺ centers in the Li₂B₄O₇:Cr and KLiB₄O₇:Cr glasses were measured and analyzed. All transitions in optical absorption, luminescence excitation and emission spectra of these glasses are identified. Broad complex bands that peak near 615, 405, and 350 nm in optical absorption and luminescence excitation spectra correspond to the ⁴A_2g(F) → ⁴T_2g(F), ⁴A_2g(F) → ⁴T_1g(F), and ⁴A_2g(F) → ⁴T_1g(P) spin-allowed transitions of the Cr³⁺ centers in distorted octahedral sites of the tetraborate glass network. The octahedral (cubic) crystal field strength (10Dq) and Racach parameters (B and C) for Cr³⁺ centers in Li₂B₄O₇:Cr and KLiB₄O₇:Cr glasses are estimated. Narrow and broad emission bands in red – NIR regions are assigned to the ²E_g(F) → ⁴A_2g(F) (R₁ line) and ⁴T_2g(F) → ⁴A_2g(F) (electron-vibration) transitions, which correspond to the Cr³⁺ centers in high-field and low-field sites, respectively. All observed emission bands are characterized by non-exponential decay. Measured average lifetimes and local structure of the Cr³⁺ centers in high-field and low-field sites of the Li₂B₄O₇:Cr and KLiB₄O₇:Cr glass network have been discussed.     

Some studies of the optical properties of tungsten-calcium-tellurite glasses

A range of tungsten tellurite glasses containing calcium was prepared and the densities, optical absorption edges and infrared optical absorption spectra were measured. The optical energy gap is of order 3 eV, somewhat lower than for many oxide-based glasses. It is established that the main absorption bands are related to the bonds in TeO₂ rather than the other components of the glasses.     

Structure and magnetic susceptibility of irradiated sodium borate glasses containing nickel oxide

The effect of introducing soda to boric oxide on the optical absorption infrared spectra and magnetic susceptibility of sodium borate glass system containing nickel oxide was studied. It was found that increasing of Na₂O helps in forming the BO₄ group and nonbridging oxygen and the nickel ions change from the octahedral state to the tetrahedral state. The magnetic susceptibility also increases rapidly with gradual increase of soda content up to 20 mol%, and then slightly increases, this may be due to the change in the coordination number of nickel ions. Also the effect of the addition of nickel oxide was studied, it was found that the values of magnetic susceptibility increases with the gradual increase of the nickel oxide, which is due to the increase of Ni²⁺ in octahedral coordination.