Yb–Er doped composite fiber with silicate clad and phosphate core prepared by stack-and-draw method

We report on a single-clad fiber with heavily Yb–Er-doped phosphate core and silicate clad. The calculated core NA is ~0.11. The diffusion is slight between the core and clad due to the small drawing temperature contrast between the phosphate and silicate glass. A strong ASE was obtained with central wavelength of 1534 nm.     

Organic–inorganic polymer hybrids prepared by the sol-gel method

This review focuses on some aspects of organic-inorganic hybrid materials prepared by the sol-gel method. This field has been studied worldwide as one of the nanotechnologies, and is now of current interest for both organic and inorganic scientists. The elaboration of organic–inorganic polymer hybrid materials using the sol-gel process can be accomplished by various approaches. The simplest method is increasing the compatibility by using physical interactions, covalent bonding and compatibilizer between organic polymer and silica gel. Other novel approaches, such as an in-situ method, NHSG (Non- Hydrolysis Sol-Gel) process, and use of reactive polymer hybrids resulted in the preparation of novel transparent organic–inorganic polymer hybrid materials. Stimulus responsive polymer hybrids are also mentioned. Furthermore, nano-structured organic–inorganic polymer hybrids are created by using supermolecular and self-assembly of organic molecules or polymers recently. The obtained nano-structured hybrid materials showed unique properties that could not be found in amorphous hybrid materials. The possibilities and applications of organic–inorganic polymer hybrid materials are also described in this review.     

Fe–Si core/Si-shell clusters prepared by double glow discharge sources

Journal of Nanoparticle Research - Using an improved plasma gas condensation cluster deposition system, Fe and Si clusters are prepared by a single glow discharge source and Fe/Si hybrid clusters...     

Novel silicon–oxygen–carbon composite with excellent cycling steady performance as anode for lithium-ion batteries

The novel anode material for lithium-ion batteries, silicon–oxygen–carbon (Si–O–C) composite, is prepared by a liquid solidification combined with following pyrolysis process, in which silicon dioxide (SiO₂) is used as an additive agent to enhance the electrochemical performance of the composite. While the structure of the composite is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR), the morphology and microstructure were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. SEM and TEM observations reveal that the Si–O–C powders are about 1 μm in diameter, and there is a homogenous pyrolyzed carbon layer about 5 nm thick on the surface of the particle. The Si–O–C sample as anode material can deliver a high initial charge capacity of 753.4 mAh g^?1, and the capacity keeps above 500.0 mAh g^?1 after 40 cycles at 100.0 mA g^?1. The electrochemical impedance spectroscopy results show that the composite exhibits lower charge transfer resistance and higher lithium-ion diffusion rate compared with the Si–C anode, which indicates that the composite Si–O–C could be used as a promising anode material for lithium-ion batteries.

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Graphical Abstract SEM images of the Si-C (a) and Si-O-C (b) samples and the TEM (c) and HRTEM (d) image of the Si-O-C sample

     

Photoconductivity studies on nanoporous TiO2/dopamine films prepared by sol–gel method

Dopamine was encapsulated into nanoporous amorphous TiO₂ matrix by sol–gel method under atmospheric conditions. A second sample was obtained by the addition of the crown-ether 15C5 in this previous sample. Thin films were spin-coated on glass wafers. No heat treatment was employed in both films. All films were characterized using infrared spectroscopy, high resolution transmission electronic microscopy, X-ray diffraction, optical absorption and scanning electronic microscopy. Despite the films prepared with 15C5 were no calcined, a partial crystallization was identified. Anatase and rutile nanoparticles with sizes of 4–5 nm were obtained. Photoconductivity technique was used to determine the charge transport mechanism on these films. Experimental data were fitted with straight lines at darkness and under illumination wavelengths at 320, 400, and 515 nm. It indicates an ohmic behavior. Photovoltaic and photoconductivity parameters were determined from the current density vs. the applied-electrical-field results. Amorphous film has bigger photovoltaic and photoconductive parameters than the partially crystalline film. Results observed in the present investigation prove that the nanoporous TiO₂ matrix can protect the dopamine inhibiting its chemical instability. This fact modifies the optical, physical and electrical properties of the film, and is intensified when 15C5 is added.     

Balance the oxidation resistance and mechanical properties of C/Si–C–N composite by a Si–O–C interphase

Carbon fiber reinforced Si–C–N matrix composite with a Si–O–C interphase (C/Si–O–C/Si–C–N) was fabricated via chemical vapor infiltration and polymer impregnation and pyrolysis process. The mechanical properties and oxidation behaviors of C/Si–O–C/Si–C–N were investigated using three-point-bending test and thermogravimetry. The results indicated that the oxidation resistance of C/Si–O–C/Si–C–N was improved as compared to C/Si–C–N with pyrolytic carbon (PyC) interphase (C/PyC/Si–C–N). The higher oxidation resistance of C/Si–O–C/Si–C–N attributed to the high inoxidizability of Si–O–C interlayer and low thermal stress in matrix. The flexural strength of C/Si–O–C/Si–C–N rivaled that of C/PyC/Si–C–N and the modulus was higher than that of C/PyC/Si–C–N. The suitable interphase and the optimized interface bonding can get the high oxidation resistance of the composites with the mechanical properties maintained.     

Capacitance–voltage and conductance–voltage characteristics of Ag/n-CdO/p-Si MIS structure prepared by sol–gel method

The frequency dependent electrical properties of Ag/n-CdO/p-Si structure has been investigated using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics in the frequency range 10 kHz–1 MHz in the room temperature. The increase in capacitance at lower frequencies is observed as a signature of interface states. The presence of the interfaces states (N_SS) is also evidenced as a peak in the capacitance–frequency characteristics. Furthermore, the voltage and frequency dependence of series resistance were calculated from the C–V and G/ω–V measurements and plotted as functions of voltage and frequency. The distribution profile of R_S–V gives a peak in the depletion region at low frequencies and disappears with increasing frequencies. The values of interface state densities and series resistance from capacitance–voltage-frequency (C–V-f) and conductance–voltage-frequency (G/ω–V-f) measurements were obtained in the ranges of 1.44×10¹⁶–7.59×10¹² cm^?2 eV^?1 and 341.49–8.77 Ω, respectively. The obtained results show that the C–V-f and G/ω–V-f characteristics confirm that the interface states density (N_SS) and series resistance (R_S) of the diode are important parameters that strongly influence the electrical parameters in Ag/n-CdO/p-Si structures.     

A comparative study on the nanocrystalline ZnO thin films prepared by ultrasonic spray and sol⿿gel method

Nanocrystalline ZnO thin films are deposited through two different chemical methods: (i) the films prepared by ultrasonic spray with 0.1 M and (ii) dip-coating from zinc acetate complex solutions with 0.5 M, the films obtained at different temperatures. The XRD analyses indicated that ZnO films have nanocrystalline hexagonal structure with (0 0 2) preferential orientation and the maximum crystallite size value of 103 nm measured from the films prepared by dip-coating. UV?vis measurement indicated that all films are transparency in the visible region. The optical band gap increased with decreasing of the Urbach tail energy indicating that the increase in the transition tail width and decrease of the defects, respectively.     

Enhanced electrochemical performance of LiFePO4/C prepared by sol–gel synthesis with dry ball-milling

LiFePO₄/C was prepared by a modified aqueous sol–gel route developed by incorporating an additional ball-milling step where the dry gel was milled with the additives of synthetic graphite and carbon black. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and elemental analysis. Results showed that the LiFePO₄/C synthesized by suitable ball-milling process had pure, fine and homogenous LiFePO₄ particles. Results of cyclic voltammetry and charge/discharge plateaus demonstrated that the LiFePO₄/C composite synthesized by milling for 2 h had much better electrochemical kinetics. High performances were achieved with its discharge capacities of 157 mA h g^?1 at 0.1?C and 133 mA h g^?1 at 1?C between 2.5 and 4.2 V (1?C?=?170 mA g^?1). And no obvious capacity fading was observed upon cycling. The simple and convenient synthesis route is promising for large-scale production of LiFePO₄/C.     

Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol–Gel method

Bulk monolithic samples of γ-Fe₂O₃/SiO₂ composites with different iron oxide/silica ratios have been prepared by the sol–gel technique. Iron oxide nanoparticles are obtained in-situ during heat treatment of samples and silica matrix consolidation. Preparation method was previously optimized to minimize the percentage of antiferromagnetic α-Fe₂O₃ and parallelepipeds of roughly 2×5×12 mm³, with good mechanical stability, are obtained. RT magnetization curves show a non-hysteretic behavior. Thus, magnetization measurements have been well fitted to an expression that combines the Langevin equation with an additional linear term, indicating that some of the nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and electron microscopy measurements. Zero field cooled /field cooled experiments show curves with slightly different shapes, depending on the size and shape distribution of nanoparticles for a given composition. Magneto-optical Faraday effect measurements show that the Faraday rotation is proportional to magnetization of the samples, as expected. As a demonstration of their sensing possibilities, the relative intensity of polarized light, measured at 5° from the extinction angle, was plotted versus applied magnetic field.     

Synthesis and characterization of nanostructural CuS–ZnS binary compound thin films prepared by spray pyrolysis

We have investigated the effect of zinc concentration ([Zn]/[Cu]=0–100 at%) on nanostructural, optical and electrical properties of CuS–ZnS binary thin films grown on glass substrate by the spray pyrolysis technique. X-ray diffraction analysis showed that the films were crystallized with mixed structures of CuS hexagonal and ZnS cubic structure. UV–vis optical measurements analysis showed that these binary films have a relatively high absorption coefficient (～10⁵ cm^?1) in the visible spectrum with a direct band gap in the range of 2.57–2.45 eV in agreement with the corresponding room temperature PL spectra. The electrical studies showed that all these samples have a p-type conductivity and the free hole density decreases with increasing [Zn]/[Cu] molar ratio, in agreement with the reflectance spectra of the layers, originating from plasma oscillations.     

Synthesis,characterization and mechanical properties of nylon–silver composite nanofibers prepared by electrospinning

Silver (Ag) nanoparticles (∼3 nm) were synthesized using silver nitrate as the starting precursor, ethylene glycol as solvent and poly (N-vinylpyrrolidone) (PVP) introduced as a capping agent. These nano-Ag particles were reinforced in nylon matrix by electrospinning of nylon-6/Ag solution in 2,2,2-trifluoroethanol and composite nanofibrous membranes were synthesized. The effects of solution concentration and relative humidity (RH) on the resultant fibrous membranes were studied. Scanning electron microscopy and Transmission electron microscopy was used to study the size and morphology of the fibers. It was observed that concentration and RH could be used to modulate the fiber diameter. Tensile test was used to evaluate the mechanical property of these electrospun composite membranes. The composite membranes showed higher strength (approx. 2–3 times increase in strength) compare to as synthesized nylon fibers.     

Magnetoimpedance in La0.67Pb0.33MnO3 manganite prepared by sol–gel method

In the present work, manganite La_0.67Pb_0.33MnO₃ was prepared by the sol–gel method. The difference between metal–insulator transition temperature T_MI (217 K) and Curie temperature T_c (342 K) in the sol–gel nanocrystalline manganite is mainly due to the grain boundary effect. The breaking of Mn–O–Mn bonds and strong scattering at the grain boundary cumber the transport. At room temperature 300 K, impedance and resistance increase with increasing frequency of ac currents. The observed dc magnetoresistance in sol–gel La_0.67Pb_0.33MnO₃ is related to the spin-polarized inter-grain tunneling and spin-dependent scattering at grain boundaries. The sol–gel manganite shows the magnetoimpedance characteristics, which are different from those of traditional sintered manganites and metallic giant magnetoimpedance materials. For sol–gel La_0.67Pb_0.33MnO₃ at low frequencies, the impedance experiences a peak under a low longitudinal field. In contrast, at high frequencies the peak phenomenon disappears, and the impedance drops sharply with low fields, which is due to the inter-grain or grain boundary effect. The permeability also sensitively varies with an application of transverse field. The magnetoimpedance effect in sol–gel nanocrystalline manganite is influenced by both field-induced permeability change and dc magnetoresistance.     

Microstructure and dielectric properties of PMN–PT ceramics prepared by the molten salts method

The sintering characteristic and dielectric properties of 0.67PMN–0.33PT ceramics prepared by the molten salt synthesis (MSS) method were investigated. PMN–PT particles synthesized by MSS with smaller grain size and good dispersion could lower the sintering temperature of ceramics; PMN–PT ceramics with relative density above 96% could be obtained in the range 1150–1180 °C. The molten salts species could significantly affect the microstructure and properties of MPN-PT ceramics. In the range 1100–1200 °C, PMN–PT ceramics from the sulfate flux MSS powders showed intergranular fracture, but that from the chloride flux MSS powder showed transgranular fracture. At the same sintering condition, the properties of PMN–PT ceramics from the powders prepared in the chloride flux are better than that from the powders prepared in the sulfate flux, their maximum dielectric constant ε_max≈29,385 and piezoelectric constant d₃₃≈660 pC/N. The above results demonstrated that PMN–PT ceramics prepared by the molten salts method possessed excellent piezoelectric and dielectric properties.     

Li–N dual-doped ZnO thin films prepared by an ion beam enhanced deposition method

Li–N dual-doped ZnO films [ZnO:(Li,N)] with Li doping concentrations of 3 at.%–5 at.% were grown on a glass substrate using an ion beam enhanced deposition(IBED) method. An optimal p-type ZnO:(Li,N) film with the resistivity of 11.4 Ω·cm was obtained by doping 4 at.% of Li and 5 sccm flow ratio of N2. The ZnO:(Li,N) films exhibited a wurtzite structure and good transmittance in the visible region. The p-type conductive mechanism of ZnO:(Li,N) films are attributed to the Li substitute Zn site(LiZn) acceptor. N doping in ZnO can forms the Lii–NOcomplex, which depresses the compensation of Li occupy interstitial site(Lii) donors for LiZnacceptor and helps to achieve p-type ZnO:(Li,N) films. Room temperature photoluminescence measurements indicate that the UV peak(381 nm) is due to the shallow acceptors LiZnin the p-type ZnO:(Li,N) films. The band gap of the ZnO:(Li,N) films has a red-shift after p-type doping.     

The magnetic properties,thermal stability and microstructure of Nd–Fe–B/Ga sintered magnets prepared by blending method

The effect of gallium added by blending method on the magnetic properties, thermal stability and microstructure of Nd_16.5Dy_16.0Fe_53.45Co_13.0B_1.05 (wt%) sintered magnets was investigated. The experimental results show that an appropriate Ga addition can markedly increase the coercivity, reduce the irreversible loss and slightly enhance the remanence. For instance, by adding 0.5 wt% Ga, the coercivity is increased from 1232 to 1819 kA/m; the irreversible loss after being exposed at 200°C for 0.5 h is reduced from above 33% to below 5%. Microstructure analyses show that the grain boundaries of the magnets with and without Ga addition are substantially different. The grain boundaries of the Ga-free magnet are meandrous. On the other hand, most of the boundaries of Ga-containing magnets are straight and smooth. These characteristics can be explained by the appearance of new phases during sintering process.     

Eu-doped B2O3–ZnO–PbO glass phosphor powders with?spherical shape and fine size prepared by spray pyrolysis

Eu-doped B₂O₃–ZnO–PbO glass phosphor powders with spherical shape and fine size were directly prepared by spray pyrolysis. The glass phosphor powders prepared at a temperature of 1100°C had broad XRD peak at around 28°. One glass phosphor powder was formed from one droplet at the preparation temperature range from 900 to 1100°C. The mean size of the glass phosphor powders was 0.75 μm. The glass transition temperature (T _g ) of the glass phosphor powders prepared by spray pyrolysis was 378.5°C. The excitation spectrum of the glass phosphor powders prepared at the optimum preparation temperature of 1100°C had bands at 362, 381, 392, 463, 525, and 532 nm. The glass phosphor powders had emission spectra with bands at 579, 614, and 653 nm. The glass phosphor powders with doping concentration of Eu of 7 wt% had the maximum photoluminescence intensity. The glass phosphor layer formed from the glass phosphor powders had high transparencies above 90%.     

Efficient UV-light photocatalytic activity of TiO2@Phosphogypsum composite synthesized by sol–gel method

Optical and Quantum Electronics - All optical multiband radio transceiver is designed using Polarization Modulators. Polarization Modulators have been gaining popularity in recent times as the...