Electrical and optical properties of µc-SiH films

Microcrystalline silicon films have been found quite useful in amorphous silicon solar cells as a contact material in n-i-p cells. Microcrystalline silicon films are obtained when amorphous silicon films are prepared by R.F. glow discharge of SiH₄ + H₂ at higher power ratings. These films possess higher conductivity as well as high transmission than amorphous silicon films. The present paper reports the preparation technique ofμc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane. X-ray studies andtem studies of the films indicate microcrystallinity of the films. The electrical and optical properties are also reported.     

Synthesis,structural and optical characterization of ZrO2 core–ZnO@SiO2 shell nanoparticles prepared using co-precipitation method for opto-electronic applications

Nanocrystalline Zirconia (ZrO₂) and Zinc oxide (ZnO) as well as Silica (SiO₂) coated ZrO₂ core–shell structures were synthesized by both Co-precipitation and seeded polymerization technique. The phase analysis and the core–shell structure formation were confirmed by X-ray diffraction (XRD), FESEM and high resolution transmission electron microscopy (HRTEM) analysis. The existence of SiO₂ on ZrO₂@ZnO was characterized by FT-IR measurement. UV–Vis study reveals coating of ZnO over Zirconia shows red shift in the absorption spectra. Photoluminescence studies show the non-monotonous variation in luminescence behavior of these core–shell nanoparticles. This investigation explains that the interfacial effect between the core (ZrO₂) and the shell materials (ZnO and SiO₂) can be exploited to tune the optical properties of the material. This implies that we can envisage the core–shell materials as potential candidates for optical–electronic devices.     

Effect of pressure on the phase composition of Li(Na)/W/Mn/SiO2 composites and their catalytic activity for oxidative coupling of methane

The phase state of Li/W/Mn/SiO₂ and Na/W/Mn/SiO₂ composites after exposure to high pressures (2.5 GPa at 500°C) and subsequent exploitation in oxidative coupling of methane (OCM) was studied. Comparison of the catalytic activity of the composites before and after exposure to high pressures indicates that the formation of Li(Na)/W/Mn/SiO₂ composites catalytically active for OCM is significantly influenced by high pressures.     

The identification of a grain-boundary phase in hot-pressed silicon nitride by Auger electron spectroscopy

The presence of magnesium, calcium and oxygen has been detected in the intergranular fracture surface of an Si₃N₄-7% MgO hot-pressed material by Auger electron spectroscopy, together with a chemical shift in the silicon Auger peak. The composition of this grain-boundary phase has been estimated as (0.40 ± 0.03) CaO. (0.75 ± 0.10) MgO. 2SiO₂ by comparison with spectra obtained from a bulk glass specimen of similar composition. The reduction in strength of the hot-pressed material at temperatures above 1000° C has been attributed to the decrease in viscosity of this phase.     

Low temperature sintering and characteristics of K2O–B2O3–SiO2–Al2O3 glass/ceramic composites for LTCC applications

The K₂O–B₂O₃–SiO₂, K₂O–B₂O₃–SiO₂–2 %Al₂O₃, K₂O–B₂O₃–SiO₂–4 %Al₂O₃ glasses with different Al₂O₃ content were prepared. Different proportions (50, 55, 60, 65, 70 %) of the three glasses were respectively mixed with alumina ceramic-filler, then the mechanical and dielectric properties were investigated. The results showed K₂O–B₂O₃–SiO₂–2 %Al₂O₃ glass/alumina filler (glass:alumina = 60:40) had the excellent comprehensive properties, so further study was continued with part of alumina ceramic-filler replaced by the silica ceramic-filler on this composite. Then the X-ray diffraction analysis revealed that the alumina and silica fillers existed as the crystal phase, and the densification was seriously damaged when the silica content reached to three quarters of the fillers. With the increase of the silica-filler, the composites’ density and dielectric constant exhibited uniform decrease, but thermal expansion coefficient (TEC) uniformly increased. When the glass:alumina:silica was equal to 60:30:10, a best composite property was presented as a bulk density of 2.582 (g cm^?1), a dielectric constant of 6.1 and a dielectric loss of 2 × 10^?3 at 1 MHz, a flexural strength of 168 MPa, and a TEC of 8.62 × 10^?6 °C^?1.     

Flux growth of silicates with vapour transported silicon

As a result of a proposed vapour transport mechanism, silicate crystals have been grown from fluxed melts which originally contained only trace amounts of silicon. The melts were contained in platinum crucibles in a sillimanite, Al₂SiO₅, muffle, and the flux consisted of PbF₂, or PbF₂ + PbO, occasionally with additional MoO₃. It is postulated that a volatile siliceous species resulted from the reaction of PbF₂ vapour with the muffle and that this species transported Si into the fluxed melts. The silicate crystals produced include Er₂SiO₅, Dy₂SiO₅, Mg₂SiO₄·MgF₂, a new material of formula Dy₄SiO₈, and several new rare earth compounds with the apatite structure.     

Influence of Al2O3/SiO2 ratio on the microstructure and properties of low temperature co-fired CaO–Al2O3–SiO2 based ceramics

In this work, in order to obtain the materials for low temperature co-fired ceramics applications, CaO–Al₂O₃–SiO₂ (CAS) based ceramics were synthesized at a low sintering temperature of 900 °C. The influences of Al₂O₃/SiO₂ ratio on the microstructure, mechanical, electrical and thermal properties were studied. According to the X-ray diffractomer and scanning electron microscopy results, the addition of the Al₂O₃ is advantageous for the formation of the desired materials. Anorthite(CaAl₂Si₂O₈) is the major crystal phase of the ceramics, and the SiO₂ phase is identified as the secondary crystal phase. No new crystal phase appears in the ceramics with the increasing Al₂O₃ content. More or less Al₂O₃ addition would all worsen the sintering, mechanical and dielectric properties of CAS based ceramics. The ceramic specimen (Al₂O₃/SiO₂ = 20/18.5) sintered at 900 °C shows good properties: high bending strength = 145 MPa, low dielectric constant = 5.8, low dielectric loss = 1.3 × 10^?3 and low coefficient of thermal expansion value = 5.3 × 10^?6 K^?1. The results indicate that the prepared CAS based ceramic is one of the candidates for low temperature co-fired ceramic applications.     

Lead-free piezoelectric composites with high piezoelectric performance and high dielectric constant caused by percolation phenomenon

We report on lead-free piezoelectric composite with high dielectric constant (ε _r > 10⁵) and the d ₃₃ (above 70 pC/N) comparable to typical lead based piezoelectric composites, or even higher, reaching as high as 107 pC/N. We achieved this through the combination of the good piezoelectric properties of the alkaline niobate (KNN) based perovskite with the flexibility of polymer poly(vinylidene fluoride) (PVDF). The dielectric properties observed in the KNN–PVDF-based piezoelectric composite were well explained in terms of an interfacial percolation model.     

Preparation and properties of transparent conductive N-doped CuAlO2 films using N2O as the N source

N-doped CuAlO₂ films were prepared by RF magnetron sputtering on quartz substrates using N₂O as the N source. N concentration in the films is detected by Auger electron spectroscopy in detail, which confirms that N is indeed incorporated into the films. The optical and electrical properties of transparent conductive N-doped CuAlO₂ films are modulated by the N₂O flow ratio in sputtering gas. The N-doped films have a visible transmittance of 60–70 % and a high infrared transmittance of ~85 %. The film deposited by using 15 % N₂O flow ratio with the optimal crystalline is provided with a conductivity of 3.75 × 10^?2 S cm^?1 at room temperature, which improves over one order of magnitude compared with the undoped film. The enhanced conductive property is mainly originated from the ionization of acceptor impurities.     

Investigation of phase intergrowth morphologies in the system Zn2SiO4-SiO2 by photo-emission electron microscopy

By means of photo-emission electron microscopy, which is described briefly, X-ray diffraction and electron microprobe analysis the hypo- and hypereutectic solidification in the system Zn₂SiO₄-SiO₂ has been investigated. Faceted (idiomorphic) growth of stableα? and metastableΒ-zinc silicate with some excess SiO₂ on the hypoeutectic side of the phase diagram and a metastable region of liquid immiscibility on the SiO₂-rich (hypereutectic) side determine the respective phase intergrowth morphologies. Unconstrained eutectic solidification causes a “divorced eutectic” where the zinc silicate constituent grows first from the undercooled liquid, which is simultaneously enriched in SiO₂.     

Thermal Conductivity of n-Aluminium Nitride-Added MgB2 Superconductor in Normal and Superconducting State

Thermal conductivity (k) of 0, 5, 10, and 15 wt.% aluminium nitride (n-AlN)-added polycrystalline MgB ₂ superconductors, synthesized by solid reaction is discussed both in the normal and superconducting states between 20 and 300 K. The prepared samples are characterized using X-ray diffraction (XRD) and field electron gun scanning electron microscope (FEG–SEM). Resistivity measurement confirms a decrease in superconducting transition temperature of MgB ₂ (T _c=38.5 K) with n-AlN addition and decreases to ～35 K in case of 15 wt.% n-AlN-added MgB ₂ sample. Thermal conductivity of both MgB ₂ and n-AlN-added MgB ₂ pellets does not show any hump around T _c, and the absolute values of k decrease with increasing n-AlN in MgB ₂. Temperature dependence of the thermal conductivity of MgB ₂ and n-AlN-added MgB ₂ has been analyzed, assuming the role of both electrons and phonons. The Wiedemann–Franz law does not work well for the present samples, which indicates inelastic scattering (L _eff < L ₀). Thermal conductivity of MgB ₂ and n-AlN-added MgB ₂ pellets is explained by assuming effective Lorentz number, L _eff= 0.1 L ₀. Electronic thermal conductivity in superconducting state ( \(k_{\text {el}}^{\mathrm {s}} )\) follows “two-gap model” and has been used to estimate the values of band gaps, relative contribution of each band in thermal transport, and intraband scattering relaxation time. The estimated values are fairly consistent with the previously reported results for MgB ₂. We further confirm that n-AlN addition in MgB ₂ introduces disorders in π bands, which reduce the π band gapsand intraband relaxation time ( \(\tau _{\pi }^{\text {im}})\) . The lattice contribution of thermal conductivity in both normal and superconducting states is analyzed in the terms of Callaway’s model, assuming various phonon scatterings. Our analysis indicates that the lattice thermal conductivity of MgB ₂ is dominated by phonon-sheet-like fault scattering. Addition of n-AlN in MgB ₂ enhances the phonon scattering from sheet-like faults, and dislocations induced strain field scattering by >7 times compared to that for pure MgB ₂ pellets.     

Enhancing the antifouling property of poly(vinylidene fluoride)/SiO2 hybrid membrane through TIPS method

PVDF/SiO₂ hybrid membranes with outstanding antifouling property were prepared from PVDF/glycerol triacetate system via thermally induced phase separation method, and characterized by scanning electron microscope, energy dispersive X-ray spectrometer analyses, differential scanning calorimeter, and wide angle X-ray diffraction. Their properties such as permeability, porosity, pore size distribution, and mechanical performance were also determined. The results show that SiO₂ nanoparticles modified by 3-aminopropyltriethoxysilane can be uniformly dispersed in membranes due to improved compatibility between PVDF solution and nanoparticles. The addition of SiO₂ particles to PVDF/glycerol triacetate mixture has a strong effect on crystallinity of the resulting hybrid membrane, which does not affect the type of PVDF crystal structure. Water flux recovery ratio is significantly increased from 11.7 % for pure PVDF membrane to 93.8 % for PVDF/SiO₂ hybrid membrane with addition of 8 wt% modified SiO₂. This remarkable promotion is related to the implantation of SiO₂ nanoparticles into the inner surface of membrane, which effectively restrains the adsorption of bovine serum albumin on the pore walls and improves antifouling property of the final membranes. Additionally, pure water flux of the hybrid membrane is increased by 276 %, i.e., from 85 to 320 L m^?2 h^?1, tensile strength is increased by 26.5 %, and elongation at break is increased by 85.4 % compared with that of pure membrane.     

The composition of crystals of bismuth silicon oxide

Crystals of Bi _x SiO_1.5x+2 with x ～ 12 can be pulled at rates of about 5 mm h^?1 from platinum crucibles in oxidizing atmospheres. Melts with x in the range 10 < x < 15 give crystals in which the range of x is only from x = 11.77± 0.03 to x = 12.05 ± 0.10. As a function of melt composition, the solid composition shows a minimum and a maximum. Growth from melts giving either extreme, results in crystals having a constant composition.     

Application of Fourier transform infrared spectroscopy in cement Alkali quantification

Alkali in cement is responsible for the Alkali–silica-reaction phenomenon that manifests itself in the form of premature cracking in concrete structures such as bridge decks and concrete pavements. X-ray fluorescence spectroscopy (XRF) is commonly used for cement Alkali quantification but a simpler and faster analytical procedure based on Fourier transform infrared spectroscopy (FTIR) has been expanded for this purpose. An analytical absorption band at 750 cm^?1 in the FTIR spectra of cement samples belonging to Alkali solid solution of tricalcium aluminate [C₃A(ss)] is used for Alkali quantification. Regression analysis of a plot correlating FTIR absorption band area ratio (750/923 cm^?1) to equivalent Alkali Na₂O _e (Na₂O _e  = % Na₂O + 0.658 × % K₂O) measured by XRF shows a linear correlation coefficient, R ², of 0.97. High Alkali cement samples show a higher microstructural disorder coefficient, C _d, which is a reactivity criterion introduced by Bachiorrini and co-authors (Proceedings of the seventh international conference on concrete alkali-aggregate reactions? 1986) for ASR-susceptible aggregates. Results of this research indicate applicability of FTIR technique to quantitatively predict cement vulnerability to ASR through the \( A_{{750\,{\text{cm}}^{ - 1} }} \) to \( A_{{923\,{\text{cm}}^{ - 1} }} \) band area ratio and the magnitude of the disorder coefficient (C _d).     

Structure and Magnetic Properties of Mn-doped CoFe 2 O 4 Nanoparticles Prepared by Solvothermal Route

Spinel Co_1?xMn_xFe₂ O ₄ (x = 0, 0.25, 0.5, 0.75 and 1.0) nanoparticles were synthesized by a solvothermal method using polyethylene glycol (PEG) as a surfactant. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES) spectroscopy and vibrating sample magnetometer (VSM) techniques were used to characterize phase, morphology, valence states, and magnetic properties of the samples. XRD analysis showed single phase of spinel structure, and the decrease of lattice constant on the effective Mn substitution was investigated. The effect of the PEG on the spherical aggregates of Co_1?xMn_xFe₂ O ₄ nanoparticles was observed. The result of XANES spectra showed Mn²⁺/Mn³⁺, Fe³⁺, and Co²⁺ exist in the samples. The samples showed ferromagnetism at room temperature with a maximum saturated magnetization of 72 emu/g and the smallest coercivity of 45 Oe for x = 1.0. The origin of ferromagnetic behavior is believed to be due to the occupation of Mn²⁺/Mn³⁺ ions.     

Maximum SiO2 layer thickness by utilizing polyethylene glycol as the surfactant in synthesis of core/shell structured TiO2–SiO2 nano-composites

TiO₂–SiO₂ nano-composites with the core/shell structure have been prepared by means of a technique based on an extension of well-known Stöber process. In this way, the silica coating of TiO₂ nano-particles in the presence of various commercially available surfactants of cationic, anionic and nonionic has been conducted with the aim to increase barrier properties against UV (UV blocking) radiation, in order to optimize photo-killing ability of the TiO₂ nano-particles and decline of the high photo-catalytic property of titania. The influences of varying coating parameters such as time and temperature on the silica content of nano-composites have been studied and optimum conditions for attaining a thick layer of SiO₂ have been determined. Electro-phoretic mobility measurements indicated that the silica coating shifted the iso-electric point of titania toward that of a typical pure colloidal silica. Surface elemental composition of core/shell structured TiO₂–SiO₂ nano-composites was verified by using energy dispersive X-ray analysis. It was found that maximum silica shell thickness can be obtained in the presence of polyethylene glycol as a nonionic surfactant at 80 °C for 360 min. The photo-catalytic activities were evaluated by the degradation of an aqueous solution of methylene blue under UV light irradiation. In addition, the resultant optimum nano-composites have been characterized by FESEM, TEM, BET, FTIR and UV–Vis spectroscopy.     

Near-white light luminescent material from Eu(III) complexes encapsulated in silica/PMMA matrices

A novel ternary molecular hybrid material has been obtained by immobilization of Eu-Salen complex into silica matrix and poly (methyl methacrylate) (PMMA) matrix. Here, the Salen-type Schiff-base ligand H₂Salen (N,N′-bis(salicylidene)ethylenediamine) which has been successfully modified by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) has been used as a flexible linker and the antenna. The obtained solid hybrid material shows not only the characteristic red emission of Eu³⁺ but also the blue emission of Salen-Si host arising from the inefficient energy transfer from antenna to Eu³⁺, leading to the unexpected near-white light color of the material. For comparison, the binary hybrid without PMMA has also been prepared. Photoluminescent spectra suggest that the introduction of PMMA can enhance the emission intensity whereas the chromaticity nearly has not been changed. Moreover, thermal analysis has revealed the good thermal stability of the ternary hybrid material. X-ray diffraction patterns demonstrate the amorphous structure of both hybrid materials.     

The effect of nanographite addition on the physical properties of poly(vinylidene fluoride)/hydroxypropyl cellulose blend

In this study, polymeric films of poly(vinylidene fluoride) (PVDF)/hydroxypropyl cellulose (HPC) blend filled with various graphite-nanoparticles (GNP) contents were prepared via solvent-mixing technique. The compatibility between PVDF and HPC polymers was studied. The variations in structure, dielectric and thermal properties were investigated over the frequency range (20 Hz–3 MHz) and temperature range (20–110 °C). The X-ray diffraction and differential scanning calorimetry results reveal that the crystallinity of PVDF was affected by the presence of HPC and GNP. The dielectric results reveal that the great enhancement of dielectric constant ( \(\upvarepsilon^{{\prime }}\) ) and ac conductivity (σ_ac) were observed. The dielectric properties were explained in terms of the dielectric polarization mechanism. Both HPC and GNP additions enhance the \(\upvarepsilon^{{\prime }}\) of PVDF due to the formation of β-phase polymorph and the interface effect between the GNP and blend matrix. The improvement of the thermal stability was observed due to the regular arrangement of the side chains. The easy processing, high dielectric constant, low tangent loss and high thermal stability of the composites make the composites attractive for practical applications in embedded capacitors.     

The use of mesoporous silica in the removal of Cu(I) from the cyanidation process

This research proposed the use of a mesoporous silica material (SiO₂) as a Cu(I) adsorbent in a pre-treatment of cyanide effluents employed in gold and silver extraction. Two copper sources were employed: a [Cu(CN) _X ]^?(X+1) standard solution, and a cyanide solution obtained from an ore of Peña de Bernal, Chihuahua, México, which was named Cu(I)–CN–PB. Mesoporous silica removes around 90 % of the Cu(I)–CN at 30 min in Cu(I)–CN solutions with 50 ppm of the metals; while, in a solution with a high concentration of copper (311 ppm), around 52 % was removed. The adsorption dates were adjusted following the Langmuir model; obtained a maximum adsorption capacity (Q ₀) of 8.01 mg g^?1 and a separation factor (R _L) lower than one, which indicates a favorable thermodynamic adsorption process of Cu(I)–CN by SiO₂. However, a similar copper removal capability and low selectivity was observed when Cu(I)–CN–PB was employed as the copper source. Therefore, a modification on the silica’s surface with phenyl groups was performed, in order to enhance the metallic ion selectivity. IR spectroscopy and TGA/DTA analysis confirmed the coupling of organic groups; on the other hand, nitrogen adsorption indicated a decrease on the BET surface area of the silica at 76 %, a modification of the silica structure was observed with the formation of two pore diameter (3.6 and 5.37 nm); ¹³C CP-MAS NMR indicated two different chemical shifts that corresponded to the phenyl groups on the two different pores observed. Phenyl groups enhance the selectivity for copper in the cyanide effluent, increasing the removal to 99 %.