Fabrication and thermal evolution of nanoparticles in SiO2 by Zn ion implantation

SiO₂ samples were implanted with 45 keV Zn ions at doses ranging from 5×10¹⁵ to 1.0×10¹⁷ ions/cm², and were then subjected to furnace annealing at different temperatures. Several techniques, such as ultra-violet–visible spectroscopy (UV–vis), grazing incidence X-ray diffraction spectroscopy (GXRD) and atomic force microscopy (AFM), have been used to investigate formation of nanoparticles and their thermal evolution. Our results clearly show that Zn nanoparticles could be effectively formed in SiO₂ at doses higher than 5×10¹⁶ ions/cm². The subsequent thermal annealing at oxygen ambient could induce the growth of Zn nanoparticles at intermediate annealing temperature range. While at temperature above 600 °C, Zn nanoparticles could be transformed into ZnO, or even Zn₂SiO₄ nanoparticles. The results have been tentatively discussed in combination with Zn diffusion and migration obtained by Rutherford backscattering spectroscopy (RBS) measurements.     

Diffusion of chromium in chrysoberyl

Cr³⁺ diffusion in chrysoberyl (BeAl₂O₄) irradiated by H⁺ ions and electrons has been studied and compared with diffusion in non-irradiated samples. Chrysoberyl crystals were irradiated with 6 MeV H⁺ ions to fluencies of 1×10¹⁶ cm^–2 for 25 min and with 10 MeV electrons to fluencies of 2×10¹⁷ cm^–2 for 1 h. Three different types of samples, which were doped with Cr³⁺, were annealed in horizontal alumina tube furnaces by 50 K intervals in the temperature range from 1773 to 1923 K for 200 h. Scanning electron microscope–energy dispersive X-ray spectrometer (SEM–EDX) was used to measure the diffusion. Arrhenius equations for the diffusion coefficient for Cr³⁺ in the temperature range 1773–1923 K were developed:     

Structural,electrical and optical properties of SnO2 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

SnO₂ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates at different substrate temperatures (500–800 °C) by metalorganic chemical vapor deposition (MOCVD). Structural, electrical and optical properties of the films have been investigated. The films deposited at 500 and 600 °C are epitaxial SnO₂ films with orthorhombic columbite structure, and the HRTEM analysis shows a clear epitaxial relationship of columbite SnO₂(1 0 0)||YSZ(1 0 0). The films deposited at 700 and 800 °C have mixed-phase structures of rutile and columbite SnO₂. The carrier concentration of the films is in the range from 1.15×10¹⁹ to 2.68×10¹⁹ cm⁻³, and the resistivity is from 2.48×10⁻² to 1.16×10⁻² Ω cm. The absolute average transmittance of the films in the visible range exceeds 90%. The band gap of the obtained SnO₂ films is about 3.75–3.87 eV.     

Thermodynamics of the Cu/Cu-redox equilibrium in soda-silicate and soda-lime-silicate melts

The thermodynamics of the redox equilibrium of Cu⁺/Cu²⁺ were determined by square-wave voltammetry in glass melts with the base mol% compositions x Na₂O · (100 − x) SiO₂ (x = 15, 20, 26 and 33) and (26 − x) Na₂O · x CaO · 74 SiO₂ (x = 0, 5, 10 and 15) doped with 1 mol% CuO in the temperature range from 850 to 1150 °C. All recorded voltammograms showed two maxima attributed to the reductions of Cu²⁺ to Cu⁺ and Cu⁺ to metallic copper. Both peaks are shifted to smaller potentials with decreasing temperature. With increasing melt basicity, the [Cu⁺]/[Cu²⁺]-ratio first increases, and remains constant for optical basicities >0.56. The effect of composition on the redox equilibrium is explained by the incorporation of both Cu⁺ and Cu²⁺ in octahedral coordination into the melt structure.     

Copper redox behavior, structure and properties of copper lead borate glasses

Copper oxidation states, structure and properties of xCuO · (50-x)PbO · 50B₂O₃ glasses were investigated. Both infrared (IR) and ¹¹B magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies were employed to determine the tetrahedral BO₄ fraction in the glasses as a function of CuO content. IR study indicates that the replacement of Pb²⁺ by Cu²⁺ ions increases the BO₃ units by converting BO₄- containing groups into ring type metaborate groups. The oxidation states of copper ions in the glasses have been studied using both X-ray photoelectron spectroscopy (XPS) and the wet chemical method. For high CuO containing (?30 mol%) glasses, high Cu⁺ ion concentrations (Cu⁺/Cu_tot.>0.3) result in a relatively slow disproportionation of B⁴-containing groups because of the small coordination number of Cu⁺ compared to Cu²⁺ ions. Effects of both glass structure and redox states of copper ions on glass properties including density, Vickers’ hardness, coefficient of thermal expansion, and chemical durability have been discussed.     

Iron redox equilibrium, structure and properties of zinc iron phosphate glasses

Iron redox equilibrium, structure and properties were investigated for the 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glasses melted at different temperatures. The structure and valence states of the iron ions in these glasses were investigated using Mössbauer spectroscopy, Raman spectroscopy and differential thermal analysis. Mössbauer spectroscopy indicated that the concentration of Fe²⁺ ions increased in the 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glass with increasing melting temperature. The Fe²⁺/(Fe²⁺ + Fe³⁺) ratio increased from 0.18 to 0.38 as the melting temperature increased from 1100 to 1300 °C. The measured isomer shifts showed that both Fe²⁺ and Fe³⁺ ions are in octahedral coordination. It was shown that the dc conductivity strongly depended on Fe²⁺/(Fe²⁺ + Fe³⁺) ratio in glasses. The dc conductivity increases with the increasing Fe²⁺ ion content in these glasses. The conductivity arises from the polaron hopping between Fe²⁺ and Fe³⁺ ions which suggests that the conduction is electronic in nature in zinc iron phosphate glasses.     

Growth kinetics of vanadium pentoxide nanostructures under hydrothermal conditions

The work reported here involved a study of the growth kinetics of V₂O₅nH₂O nanostructures under hydrothermal conditions. The coarsening process of V₂O₅nH₂O nanoribbons was followed by subjecting the as-prepared suspensions to hydrothermal treatments at 80 °C for periods ranging from 0 to 7200 min. X-ray diffraction (XRD) confirms that the hydrothermal treatments at 80 °C caused no significant modification of the long-range order structure of samples subjected to different periods of hydrothermal treatment. Field emission scanning transmission electron microscope (FE-STEM) was used to analyze the morphology and width distribution of the nanostructures. The results indicated that the crystal growth mechanism in the [1 0 0] direction of vanadium pentoxide 1D nanostructure under hydrothermal conditions is well described by the oriented attachment (OA) mechanism. This evidence was supported by HRTEM images showing the existence of defects at the interface between nanostructures, which is characteristic of the oriented attachment (OA) mechanism.     

Influence of high temperature deformation on the fracture behavior of a bulk Zr-based metallic glass

Nanocrystalline/amorphous matrix composites obtained by isothermal compression at high temperatures and low strain rates were characterized using transmission electron microscopy. To study the influence of high temperature deformation on the fracture behavior and room temperature plasticity, compression tests with a constant strain rate of 1 × 10⁻⁴ s⁻¹ were applied to the deformed samples. Fracture features of as-cast alloy and deformed samples were analyzed using scanning electron microscopy. Compared with the as-cast alloy, the room temperature plasticity of deformed sample is not destroyed both in the range of 370-395 °C at 1 × 10⁻³ s⁻¹ and at 395 °C in 1 × 10⁻² to 1 × 10⁻³ s⁻¹, and deteriorated at higher temperatures and lower strain rates. Corresponding to the TEM images, the homogenously dispersed nanocrystals with small size contribute to the compressive plasticity, and the aggregated large nanoparticles destroy the plasticity of the sample after high temperature deformation.     

Effect of ion beam irradiation on the corrosion behavior of the melt-spun ribbon Ti60Ni40

Potentiodynamic polarization studies were carried out on unirradiated and irradiated Ti₆₀Ni₄₀ specimens in 1 M HNO₃ aqueous medium at room temperature. The irradiation was carried out using N⁺ 150 keV ions at a fluence of 1 × 10¹⁶ ions/cm². Polarization results revealed that the irradiated specimen exhibits less corrosion current density as compared to the unirradiated Ti₆₀Ni₄₀ specimen. X-ray photoelectron spectroscopy (XPS) studies were also carried out on the irradiated and unirradiated specimens after corrosion test. It was observed that the absence of Ti³⁺ species in the oxide film of the irradiated specimen as compared to the unirradiated specimen results in the improvement of the corrosion resistance. Polarization results are also corroborated by weight loss data.     

Growth rate of α-calcium sulfate hemihydrate in K–Ca–Mg–Cl–H2O systems at elevated temperature

Kinetics of calcium sulfate hemihydrate (HH) crystal growth plays an important role in mineralization of calcium sulfate phases in nature. HH crystal growth and the conversion of calcium sulfate phases form the basis for the production and application of gypsum based building material. α-HH crystals have been grown in 3.74 M CaCl₂ solutions at a fixed initial ratio of calcium to sulfate under atmospheric pressure. The variations of sulfate ions were determined to obtain the α-HH crystal growth kinetics information. Effects of Mg²⁺ and K⁺ ions on α-HH growth were investigated to find an optimal composition of solution for α-HH preparation. The orders of α-HH growing in the CaCl₂ solution were found, in most cases, to be near 2.0 in presence or in absence of Mg²⁺ and K⁺ ions. Mg²⁺ ions enhance the growth of α-HH in CaCl₂ solution mainly due to initial supersaturation enhancing effects. K⁺ ions also improve the growth rate, which has been attributed to the reduction of interfacial energy. In a Ca (3.74 M)–Mg (0.20 M)–K (0.09 M) chlorides solution, the growth rate of α-HH increases with temperature from 80 to 100 °C, and the activation energy was calculated to be 40 kJ/mol.     

Structural and optical properties of 6CaO·6SrO·7Al2O3 thin films derived by sol-gel dip coating process

The nanostructured 6CaO·6SrO·7Al₂O₃ (C6S6A7) thin films with cubic structure using calcium, strontium metals, aluminium isopropoxide and ethylene glycol monomethyl ether as stating materials has been fabricated via sol-gel route. Based on hydrolysis of Ca²⁺, Sr²⁺ and Al³⁺ in the sol-gel processing using ethylene glycol monomethyl ether as solvent have been employed as the precursor material. The films were coated on soda lime float glass by the dip coating technique and annealed at 450 °C in air atmosphere. The structure, morphology and composition of the films were investigated by Fourier transformed infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy indicating that the films were composed of C6S6A7 nanoparticles with cubic structure. The spectral transmittance of the films was measured in the wavelength range of 200-1100 nm using an UV-visible spectrometer. It has been found that the optical properties of the films significantly affected by precursor chemistry and annealing temperature due to the improvement of the crystallinity of the films with increasing annealing temperature and became stable when the annealing temperature is higher than 450 °C. The C6S6A7 films annealed at 450 °C had high transparency about 80% in wide visible range.     

Underlying reverse current mechanisms in a-Si:H p-i-n solar cell and compact SPICE modeling

The defect states in bulk of i-layer and at p⁺/i interface have been studied by using dark reverse current-voltage (J-V) measurements. The dark reverse current as a function of voltage has been analyzed on the basis of thermal generation of the carriers from mid-gap states in i-layer. Based on its behavior the thermal generation mechanism has been divided into two types. Thermal generation at lower bias (<5 V) shows V^1/2 behavior, whereas at higher bias follows an exponential dependence of voltage (>5 V). This was explained using a thermal generation zone at lower bias, which is a source of reverse currents, and its evolution towards p⁺/i interface with increasing voltage. The analytical result has shown that at lower reverse bias (V < 5 V) the defect states in the bulk of i-layer and at higher bias (V ∼ 25 V) the defect states at p⁺/i interface are contributing to the reverse currents. Reverse bias annealing (RBA) treatment which has been performed on these cells shows that a reduction of defect states more in the i-region near to the p⁺-layer and at p⁺/i interface as compared to the deep regions in bulk of i-layer. The calculated defect state density (DOS) is varying from its intrinsic value of 2.4 × 10¹⁷ cm⁻³ in the bulk of the i-layer up to 2.1 × 10¹⁹ cm⁻³ near and at p⁺/i interface. These values decrease to 7.1 × 10¹⁶ cm⁻³ and 2.7 × 10¹⁷ cm⁻³, respectively, in the samples annealed under reverse bias at 2 V. The bias dependent leakage current behavior has been modeled and implemented in simulation program with integrated circuit emphasis (SPICE) using simple circuit elements based on voltage controlled current sources (VCCS). Simulated and measured reverse leakage current characteristics are in reasonable agreement.     

Influence of annealing on the physical properties of filtered vacuum arc deposited tin oxide thin films

Tin oxide (SnO₂) thin films were deposited on UV fused silica (UVFS) substrates using filtered vacuum arc deposition (FVAD). During deposition, the substrates were at room temperature (RT). As-deposited films were annealed at 400 and 600 °C in Ar for 30 min. The film structure, composition, and surface morphology were determined as function of the annealing temperature using X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the SnO₂ thin films deposited on substrates at RT indicated that the films were amorphous, however, after the annealing the film structure became polycrystalline. The grain size of the annealed films, obtained from the XRD analysis, increased with the annealing temperature, and it was in the range 8-34 nm. The AFM analysis of the surface revealed an increase in the film surface average grain size from 15 nm to 46 nm, and the surface roughness from 0.2 to 1.8 nm, as function of the annealing temperature. The average optical transmission of the films in the visible spectrum was >80%, and increased by the annealing ∼10%. The films’ optical constants in the 250-989 nm wavelength range were determined by variable angle spectroscopic ellipsometry (VASE). The refractive indexes of as-deposited and annealed films were in the range 1.83-2.23 and 1.85-2.3, respectively. The extinction coefficients, k(λ), of as-deposited and annealed films were in the range same range ∼0-0.5. The optical energy band gap (E_g), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths, increased with the annealing temperature from 3.90 to 4.35 eV. The lowest electrical resistivity of the as-deposited tin oxide films was 7.8 × 10⁻³ Ω cm, however, film annealing resulted in highly resistive films.     

Planar waveguides by ion exchange in Er-doped tellurite glass

This work reports the preparation of planar waveguides by Ag⁺ → Na⁺ ion exchange in Er³⁺-doped tellurite glass with a composition of 75TeO₂-2GeO₂-10Na₂O-12ZnO-1Er₂O₃ (mol%). The metric, of T_x − T_g, indicates that the glass has good thermal stability. Measurments of refractive index, absorption spectrum, luminescence and lifetime were made. The glass was chemically stable during the ion exchange process. Monomode and multimode planar waveguides in the tellurite glasses have been prepared. We determined the depth of the guides, effective diffusion coefficient and the activation energy. The depths of the waveguides could be controlled by varying ion exchange temperatures and times (250-280 °C, and 3-12 h were used).     

A low silica, barium borate glass-ceramic for use as seals in planar SOFCs

A low silica, barium borate glass-ceramic for use as seals in planar SOFCs containing 64 mol%BaO, 3 mol%Al₂O₃ and 3 mol%SiO₂ was studied. Coefficient of thermal expansion (CTE) between 275-550 °C, glass transition temperature (T_g), and dilatometric softening point (T_s) of the parent glass were 11.9 × 10⁻⁶ °C⁻¹, 552 °C, and 558 °C, respectively. Glass-ceramic was produced by devitrification heat treatment at 800 °C for 100 h. It was found that nucleation heat treatment, seeding by 3 wt%ZrO₂ as glass-composite and pulverization affected the amount, size and distribution of crystalline phases. SEM-EDS and XRD results revealed that crystalline phases presented in the devitrified glass-ceramic were barium aluminate (BaAl₂O₄), barium aluminosilicate (BaAl₂Si₂O₈) possibly with boron associated in its crystal structure, and barium zirconate (BaZrO₃). CTE of the devitrified glass-ceramic was in the range of (10.1-13.0) × 10⁻⁶ °C⁻¹. Good adhesion was obtained both in the cases of glass and devitrified glass-ceramic with YSZ and AISI430 stainless steel. Interfacial phenomena between these components were discussed.     

Optical properties of Cr ion in lithium metasilicate Li2O · SiO2 transparent glass-ceramics

The optical properties of Cr³⁺ ions in lithium metasilicate (Li₂O · SiO₂) transparent glass-ceramics were investigated. The main crystalline phase precipitated was the lithium metasilicate (Li₂O · SiO₂) crystal. The percent crystallinity and crystalline size were ranging 65-75% and 20-35 nm, respectively. The color changes drastically to deep pink from emerald green upon crystallization. New and strong absorption bands appeared and the absorption intensity increases by about 10 times that in glass. These new absorption bands are found to be derived from Cr³⁺ ions in octahedral sites in the lithium metasilicate crystal lattice. Cr³⁺ ions substitute for three Li⁺ ions and occupy the distorted octahedral site between single [SiO₄]_n chains of lithium metasilicate crystal. The ligand field parameters can be estimated: 10Dq = 13 088 cm⁻¹, B = 453 cm⁻¹, Dq/B = 2.89 and C = 2036 cm⁻¹. The near-infrared luminescence centered at 1250 nm was not detected in the deep pink glass-ceramics unlike emerald green glass.     

Development and characterizations of BaO-CaO-Al2O3-SiO2 glass-ceramic sealants for intermediate temperature solid oxide fuel cell application

Several compositions based on BaO-CaO-Al₂O₃-SiO₂ (BCAS) glass system have been studied in this investigation to see their applicability as sealant for solid oxide fuel cell (SOFC). The glasses as well as the corresponding glass-ceramics have been systematically characterized by differential thermal analysis, dilatometry, X-ray diffractometry, electron microscopy and impedance analysis to examine their suitability as sealant. While the glass transition temperature (T_g) determined from DTA are within 600-665 °C, the coefficient of thermal expansion (CTE) can be tailored between 9.5 and 13.0 × 10⁻⁶ K⁻¹. These glasses are found to be well adhered with metallic interconnects, such as commercial ferritic steel (Crofer22APU), at an optimum sealing temperature of 850 °C. The shrinkage behavior of the developed glasses in their pellet form has also been investigated. The resistivities of the glass-ceramics, as obtained from impedance analysis, are found to be within 10⁴-10⁶ Ω cm at 800 °C. Under sandwiched condition between two metals, some of the developed compositions are found to maintain this high resistivity even after 100 h of operation. One of the glass compositions has shown a low leak-rate of the order of ∼10⁻⁷ Pa m² s⁻¹.     

Fluorinated nanoporous SiO2 films with ultra-low dielectric constant

Fluorinated nanoporous silica (denoted as SiO₂:F) thin films with low dielectric constant were prepared by a sol-gel method and spin coating technique. The leakage current densities of the SiO₂:F thin films were 10⁻⁸ and 3 × 10⁻⁶ A/cm² respectively for the as-deposited films and for those subjected to annealing at a temperature of 450 °C. These currents are more than one order of magnitude lower than those of the common SiO₂ films. Photoluminescent results showed strong blue-light emission and a small blue shift in the SiO₂:F films that were related to the increment of the porosity. The dielectric properties were also characterized and the k value of the annealed SiO₂:F film was found to be about 1.67. The hole size in the films is small and the size distribution is uniform for the annealed SiO₂:F samples due to the effects of fluorination. The underlying mechanism for fluorination is discussed in this paper.     

Preparation and optical properties of nanoscale MgAl2O4 powders doped with Co ions

Co²⁺-doped MgAl₂O₄ nanocrystalline powders were prepared by co-precipitation method. The gels and/or calcined samples were characterized by means of thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectrum and near-infrared absorption spectrum. MgAl₂O₄ nanocrystals were produced by calcining the gel above 800 °C, with the crystallite size of 10-30 nm in the temperature range of 800-1100 °C. The influence of pH value of precipitant solution on the dispersing of powders was studied and the result showed that Co:MgAl₂O₄ nanocrystalline powders exhibited good dispersion when pH = 11. The absorption spectrum of Co²⁺-doped MgAl₂O₄ exhibited a broad absorption band in the wavelength range of 1200-1600 nm, which indicated that Co²⁺ ions substituted for the tetrahedrally coordinated Mg²⁺ ions in the MgAl₂O₄ lattice.     

Three-dimensional structure of fast ion conducting 0.5Li2S + 0.5[(1 − x)GeS2 + xGeO2] glasses from high-energy X-ray diffraction and reverse Monte Carlo simulations

A high-energy X-ray diffraction study has been carried out on a series of 0.5Li₂S + 0.5[(1 − x)GeS₂ + xGeO₂] glasses with x = 0.0, 0.1, 0.2, 0.4, 0.6 and 0.8. Structure factors were measured to wave vectors as high as 30 Å⁻¹ resulting in atomic pair distribution functions with high real space resolution. The three dimensional atomic-scale structure of the glasses was modeled by reverse Monte Carlo simulations based on the diffraction data. Results from the simulations show that at the atomic-scale 0.5Li₂S + 0.5[(1 − x)GeS₂ + xGeO₂] glasses may be viewed as an assembly of independent chains of (Li^+-S)₂GeS_2/2 and (Li^+-O)₂GeO_2/2 tetrahedra as repeat units, where the Li ions occupy the open space between the chains. The new structure data may help understand the reasons for the sharp maximum in the Li⁺ ion conductivity at x ∼ 0.2.