Solid–liquid interface energies in the succinonitrile and succinonitrile–carbon tetrabromide eutectic system

The equilibrated grain boundary groove shapes for the commercial purity succinonitrile (SCN) and succinonitrile–carbon tetrabromide (CTB) eutectic system were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficients for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been determined to be (5.43±0.27)×10⁻⁸ Km and (5.56±0.28)×10⁻⁸ Km, respectively, with numerical method. The solid–liquid interface energies for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been obtained to be (7.86±0.79)×10⁻³ J m⁻² and (8.80±0.88)×10⁻³ J m⁻², respectively from the Gibbs–Thomson equation. The grain boundary energies in the SCN and SCN rich phase of the SCN–CTB system have been calculated to be (15.03±1.95)×10⁻³ J m⁻² and (16.51±2.15)×10⁻³ J m⁻², respectively, from the observed grain boundary groove shapes. The thermal conductivity ratios of the liquid phase to the solid phase for SCN and SCN–4 mol% CTB alloy have also been measured.     

Diffusion coefficient of K+ in ion exchanged glasses calculated from the refractive index and the Vickers hardness profiles

The top faces of float glass samples were exposed to vapors resulting from the decomposition of KNO₃ at 565 °C for up to 32 h. X-ray dispersive spectra (EDS) show that K⁺ ions migrate into the glass. The K⁺ concentration profile was obtained and its diffusion coefficient was calculated by the Boltzmann–Matano technique. The mean diffusion coefficient was approximately 10 × 10⁻¹¹ cm² s⁻¹. It was observed that the refractive index and the Vickers hardness decrease with the depth (after the removal of successive layers), and their profiles were thus obtained. These profiles enabled the calculation of the diffusion coefficient of K⁺ through the Boltzmann–Matano technique, with mean results ranging between 6 × 10⁻¹¹ and 30 × 10⁻¹¹ cm² s⁻¹.     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Influence of hydrogen on the thermomechanical properties of a-CNx:H and a-CNx films deposited by glow discharge and ion beam assisted deposition

The coefficient of thermal expansion (CTE), Young’s modulus, Poisson’s ratio, stress and hardness of a-CN_x and a-CN_x:H were investigated as a function of nitrogen concentration. Hydrogenated films were prepared by glow discharge, GD, and unhydrogenated films were prepared by ion beam assisted deposition, IBAD. Using nanohardness measurements and the thermally induced bending technique, it was possible to extract separately, Young’s modulus and Poisson’s ratio. A strong influence of hydrogen, in a-CN_x:H films, was observed on the CTE, which reaches about ∼9 × 10⁻⁶ C⁻¹, close to that of graphite (∼8 × 10⁻⁶ C⁻¹) for nitrogen concentration as low as 5 at.%. On the other hand, the CTE of unhydrogenated films increases with nitrogen concentration at a much lower rate, reaching 5.5 × 10⁻⁶ C⁻¹ for 33 at.% nitrogen.     

Dilithium dialuminium trisilicate phase obtained using coal bottom ash

The Li₂Al₂Si₃O₁₀ glass-ceramics well crystallized and with a regular morphology was produced starting from a mixture of Li₂CO₃, TiO₂, Al₂O₃ and coal bottom ash, after reducing the magnetite phase content. Its measured thermal expansion coefficient in the temperatures range from 25 °C to 300 °C is α_(25–300) = −23.4 × 10⁻⁷ °C⁻¹. This value is ≈18% smaller than that for the commercial lithium glass-ceramics (−23.4 × 10⁻⁷ °C⁻¹ to 50 × 10⁻⁷ °C⁻¹).     

Optical characterization of sputtered amorphous aluminum nitride thin films by spectroscopic ellipsometry

We have measured and analyzed the optical constants and polarized optical properties of amorphous aluminum nitride (a-AlN) thin films deposited by RF reactive magnetron sputtering onto silicon(1 1 1) and glass substrates. The optical constants were obtained by analysis of the measured ellipsometric spectra in the wavelength range 300–1400 nm, using the Cauchy–Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range 1.80–2.11 and 8.6 × 10⁻³–1.5 × 10⁻⁵, respectively. Analysis of the absorption coefficient, in the wavelength range 200–1400 nm, shows the bandgap of a-AlN thin films to be 5.84 ± 0.05 eV. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 61° and a principal angle of 64°. Measurement of the polarized optical properties reveals a high transmissivity and very low absorptivity for a-AlN films in the visible and near infrared regions. X-ray diffraction analysis confirmed the amorphous nature of the films under study.     

Properties and structure of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glass systems

(1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses were studied for the progressive percentage substitution of Na₂O for Li₂O at the constant mole of Al₂O₃ and SiO₂. The crystallization temperature at the exothermic peak increased from 898 to 939 °C when the Na₂O content increases from 0 to 0.6 mol. The coefficient of thermal expansion and density of these as-quenched glasses increase from 6.54 × 10⁻⁶ °C⁻¹ to 10.1 × 10⁻⁶ °C⁻¹ and 2.378 g cm⁻³ to 2.533 g cm⁻³ when the Na₂O content increases from 0 to 0.4 mol, respectively. The electrical resistivity has a maximum value at Na₂O · (Li₂O + Na₂O)⁻¹ = 0.4. The activation energy of crystallization decreases from 444 to 284 kJ mol⁻¹ when the Na₂O content increased from 0 to 0.4 mol. Moreover, the activation energy increases from 284 kJ mol⁻¹ to 446 kJ mol⁻¹ when the Na₂O content increased from 0.4 to 0.6 mol. The FT-IR spectra show that the symmetric stretching mode of the SiO₄ tetrahedra (1035–1054 cm⁻¹) and AlO₄ octahedra (713–763 cm⁻¹) exhibiting that the network structure is built by SiO₄ tetrahedra and AlO₄.     

Influence of TiO2 on proton conductivity in fuel cell electrolytes based on sol–gel derived P2O5–SiO2 glasses

P₂O₅–TiO₂–SiO₂ based glasses have been prepared by a sol–gel process. The glasses were characterized by structural, thermal, nitrogen adsorption–desorption and conductivity measurements. The structural formation has been confirmed by the FTIR and NMR analysis. The proton conductivity of the glasses increased linearly with increase in temperature. Glasses with an average pore size less than 2 nm showed higher values of proton conductivity in humid atmosphere. The conductivity value increased from 6.47 × 10⁻⁴ S/cm to 3.04 × 10⁻² S/cm at 70% RH in the temperature range 30–90 °C. We observed in fuel cell measurements that the performance of the E1 electrode is superior to that of the other electrodes at the same operating condition. The power density shows a similar pattern to current density.     

Dissolution behavior of ZnO–P2O5 glasses in water

Bulk binary ZnO–P₂O₅ glasses with 50–70 mol% ZnO were immersed in distilled water at 30–90 °C for up to 72 h. The immersed samples were characterized by weight loss, the change in solution pH, X-ray diffraction (XRD) analysis, scanning electron microscopy and Raman spectroscopy. Weight loss decreased with ZnO concentration for all immersion temperatures. Dissolution behavior was classified into two types in terms of weight loss and macroscopic appearance. Type I was primarily recognized in 50–60 mol% ZnO glasses. In type I, the weight loss for 72 h was relatively large (>1.0 × 10⁻⁷ kg mm⁻², >10% of initial sample weight). Raman spectra of the type I glasses indicated that the depolymerization of phosphate glass network occurred during the dissolution process. Crystalline Zn₂P₂O₇ · 3H₂O was precipitated in the water solution after immersion. Type II dissolution behavior was recognized in the 65 and 70 mol% ZnO glasses except for the 65ZnO–35P₂O₅ glass immersed at 90 °C. In the type II behavior, the weight loss for 72 h was relatively-small (<1.0 × 10⁻⁸ kg mm⁻², <1% of initial sample weight). The microstructure of the type II glass indicated selective dissolution. The dissolution process of the type II glass is discussed.     

Protein–solvent and weak protein–protein interactions in halophilic malate dehydrogenase

With the aim to correlate the solvation, stability and solubility properties of halophilic malate dehydrogenase, we characterized its weak interparticle interactions by small-angle neutron scattering in various solvents. The protein concentration dependence of the apparent radius of gyration and forward scattered intensity extrapolated from Guinier plots, and thus the second virial coefficient, A₂, were determined for each solvent condition. In NaCl 1M+2-methylpentane-2,4-diol 30%, a solvent that promotes protein crystallization, A₂ is negative, −0.4×10⁻⁴ ml mol g⁻² and indicating attractive interactions; in ammonium sulfate 3M, in which the protein precipitates at high concentrations, A₂∼0. In 2–5M NaCl, 1–3.5M NaOAc, 1–4.5M KF or 1–2M (NH₄)₂SO₄, in which the protein is very soluble, A₂ is positive with a value of the order of 0.4×10⁻⁴ ml mol g⁻² which decreases with increasing salt concentration. In MgCl₂ however, A₂ increases with increasing salt concentration from 0.2 to 1.3M.     

Comparative study on photoluminescence of amorphous and nano-crystalline YAG:Tb phosphors prepared by a combustion method

Amorphous and nano-crystalline Y₃Al₅O₁₂:Tb phosphor samples were obtained via a facile combustion method by calcination at various temperatures, using yttrium oxide and aluminum nitrite as starting materials and citric acid as fuel. XRD, FT-IR and TEM results showed that the products were amorphous if prepared at 750 °C, well-crystalline when treated above 850 °C. In addition, partially crystalline YAG phase was observed at 800 °C (in air). The excitation spectra of the samples calcined at 750 °C and 800 °C exhibited some difference in the 230–255 nm range in comparison to those of nano-crystalline YAG:Tb, i.e. an extra band centered at 250 nm was detected via Gaussian curve-fitting. Furthermore, the photoluminescence intensity of as-synthesized samples decreased obviously with increasing the crystallinity under 250 nm excitation. Contrary, it increased monotonously when altering the excitation wavelength to 323 nm. The concentration-dependent emission spectra of samples calcined at 800 °C revealed that the strongest intensity could be obtained with 10% Tb doping. Red-shifts indicated changes of the inter-atomic distances within the Tb³⁺ coordination polyhedron with increasing Tb concentration. The low temperature photoluminescence of partially crystalline YAG:10% Tb was also investigated, displaying good-resolution but reduced intensity compared to the room-temperature photoluminescence.     

Effect of silver doping on the electrical properties of a-Sb2Se3

This paper reports the effect of Ag-doping on electrical properties of a-Sb₂Se₃ in the temperature range 230–340 K and frequency range 5–100 kHz. The variation of transport properties with thermal doping has been studied. Ag-doping produces two homogeneous phases in the sample, which are found to be voltage dependent in the temperature range studied and frequency dependent in lower frequency region (0.1–10 kHz). Activation energy E_g and C′ [= σ₀ exp (γ/k), where γ, is the temperature coefficient of the band gap] calculated from dc conductivity has been found to vary from (0.42 ± 0.01) eV to (0.26 ± 0.01) eV and (4.11 ± 0.01) × 10⁻⁵ to (2.90 ± 0.02) × 10⁻⁶ Ω⁻¹ cm⁻¹ respectively. Ag-doping can be used to make the sample useful in device applications.     

Linear and nonlinear optical properties of the optical fiber doped with silicon nano-particles

We report for the first time the realization of the optical fiber doped with silicon nano-particles. Silica glass optical fibers incorporated with silicon nano-particles were fabricated by the modified chemical vapor deposition and the solution doping technique. We found that a broadband absorption appeared at 450–1300 nm and a photoluminescence band appeared at 600–1100 nm upon pumping with the Ar-ion laser, indicating that silicon nano-particles were successfully incorporated in the fiber core. We also estimated the third-order optical nonlinearity of the optical fibers by measuring the fringe shift obtained from the long-period gratings upon pumping with the Ar-ion laser from 477 to 512 nm. Importantly the optical nonlinearity at 1550 nm was found to be ～1.5 × 10^?15 m²/W and we believe that this large optical nonlinearity is caused by the exciton absorption of the silicon particles.     

Measurement of diffusion coefficients of Au in liquid Ag with the shear cell technique

Diffusion coefficients of Au in liquid Ag were measured at the temperatures 1300 K and 1500 K by using the shear cell technique. The adopted technique was a modified long capillary method which had a diffusion couple configuration. Obtained diffusion coefficients of Au in liquid Ag were respectively 2.30 × 10⁻⁹ m² s⁻¹ at 1300 K and 3.16 × 10⁻⁹ m² s⁻¹ at 1500 K, which were in good agreement with calculations based on the hard sphere mixture model.     

Nonlinear optical properties of PbS quantum dots in boro-silicate glass

PbS quantum dots synthesis in boro-silicate glass is presented. Absorption bleaching of PbS quantum dots of ≈4 and ≈7 nm in diameter dispersed in this glass has been studied. Bleaching relaxation time of 20–30 ps, absorption saturation fluence of ≈5 mJ/cm² and ground-state absorption cross-section of 2 ÷ 6 × 10⁻¹⁷ cm² at the wavelengths corresponding to the first excitonic absorption band maxima are measured.     

Sol–gel derived organic–inorganic hybrid electrolytes for thin film electrochromic devices

Sol–gel derived, lithium ion conducting organic–inorganic hybrid electrolytes for ambient temperatures applications, have been synthesized from tetraethyl orthosilicate (TEOS), poly(ethylene oxide) (PEO), propylene carbonate (PC), propylene oxide, butyl acrylate, butyl methacrylate, ethyl acetoacetate and LiClO₄ precursors. Mass fractions of the organic additions in the gels were of ca 30 mass% for gels 0/B, F–H and 40 mass% for gel J. The colorless transparent or translucent hybrid materials obtained in this work were aged at room temperature for at least three weeks and then dried at 80 °C for 3 h. The morphology and structure of all compositions were investigated by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX), Fourier transform infrared spectroscopy and ²⁹Si MAS nuclear magnetic resonance. Amorphous nature of the hybrids was confirmed by X-ray diffraction. SEM, FTIR and NMR analysis showed structural properties and [SiO₄] tetrahedrons poly-condensation process to be strongly influenced by organic additives have been employed. Room temperature ionic conductivities of the hybrid electrolytes were in a range of 9.84 × 10⁻⁴–1.56 × 10⁻³ Ω⁻¹ cm⁻¹.     

Preparation of mixed arsenic/antimony chalcogenide glasses and some optical and thermo-physical properties

The preparation of mixed glasses of As₂S_3−xSe_x (x = 0–3) and (1 − y) · As₂S₃y · Sb₂S₃ (y = 0–1) has been carried out by an in situ pouring technique. X-ray diffraction (XRD) was used to confirm the glassy nature of the materials and monitor devitrification. Visible-IR transmission, photoluminescence, refractive index and micro-Raman were measured as a function of composition. Microhardness (MH) and thermal expansion coefficient (TEC) were also measured. Raman peaks in As₂S₃ and As₂Se₃ were observed around 338 cm⁻¹ and 230 cm⁻¹, respectively in this first composition series in which S was replaced by Se. When As was replaced by Sb, in the case of second composition series, the As₂S₃ related Raman peak became broader and shifted to lower wave number, reflecting some structural change/devitrification. MH increased (1.31–1.50 GPa) with Se and Sb content while the TEC was found to decrease (2.5–1.4 × 10⁻⁵/K). The progressive increase in the content of either Se or Sb in As₂S₃ is anticipated to modify bond lengths and bond angles. The combined effect of these structural modifications would change the local structure of the glass forming a more rigid glass network thereby increasing the hardness and decreasing TEC.     

Efficient 1.53 μm erbium light emission in heavily Er-doped titania-modified aluminium tellurite glasses

Ti–Al co-doped erbium tellurite glasses have been obtained by melting mixed Er₂O₃, TiO₂ and TeO₂ batches in Al₂O₃ crucibles. By crucible dissolution Al₂O₃ amounts from 11.5 to 18.6 mol% were introduced in the synthesized glasses. Differential thermal analysis of glasses points to a strong dependence of glass transition temperature T_g with the substitution extent of TeO₂ by the doping oxides. No crystallization features are observed up to 450 °C. The spectral features and decay kinetics of the infrared photoluminescence of erbium demonstrate the possibility to achieve more than 50% of quantum yield of light-emission at Er³⁺ concentrations as large as 10²¹ cm⁻³, with about 2 ms of lifetime, 8 × 10⁻²¹ cm² of stimulated emission cross section, and no saturation at pump power densities higher than 10 kW cm⁻². The study of the kinetics of Er–Er energy transfer suggests to ascribe these features to a particularly homogeneous dispersion of Er³⁺ ions in the modified tellurite network. Raman scattering measurements of the spectral distribution of vibrational modes evidence that the introduction of doping oxides leads to an increase of structural disorder without crystallization effects.     

Absorption,emission and absorption saturation of Cr4+ ions in calcium aluminate glass

Absorption, luminescence and absorption saturation of Cr ions in a calcium aluminate glass are studied. In the absorption spectrum, the absorption bands of Cr³⁺, Cr⁴⁺ and Cr⁶⁺ ions are revealed. The emission spectrum presents luminescence of Cr³⁺ ions centered at 0.82 μm and that of Cr⁴⁺ ions at 1.3 μm. The luminescence signal demonstrates short decay times of 120 ± 10 ns and 300 ± 20 ns for Cr³⁺ and Cr⁴⁺ ions, respectively. Absorption saturation measurements allowed an estimate of the ground-state absorption cross-sections for Cr⁴⁺ ions at 1.06 μm of 0.7 × 10⁻¹⁸ cm² and at 0.69 μm of 1.5 × 10⁻¹⁸ cm².