SnO<Subscript>2</Subscript>-core/SiO<Subscript>x</Subscript>-shell coaxial whiskers with a needle-like morphology

Needle-shaped structures of tin oxide (SnO₂) were coated with a shell layer of SiO_x via a sputtering method. The diameters of the SiO_x-coated structures gradually became thinner, leading to the formation of sharp tips. The whiskers consisted of a crystalline SnO₂ core surrounded by an amorphous SiO_x shell. The photoluminescence (PL) spectrum with a Gaussian fitting exhibited yellow-green and orange light emission bands, and the overall shape and intensity of the PL spectrum were not changed by the SiO_xcoating. The results of this study suggest that sputtering can be employed to achieve the layered growth of shell layers on a variety of nanostructures.     

Effect of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> doping on the structure,magnetic properties and electrical properties of La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

The (La_0.7Ca_0.3MnO₃)_1x /(NiFe₂O₄) _x (x = 0 to 0.09) composites were prepared using a conventional solid state reaction method. The structural, magnetic properties, and electrical properties of LCMO/NFO composites were investigated using X-ray diffraction, scanning electron microscopy, field cooled DC magnetization, and magnetoresistance (MR) measurements. The resistivity measured as a function temperature demonstrates that the pure LCMO and x = 0.01 samples display metal to semiconductor transitions. However, the composites of x > 0.03 samples clearly present the electrical behavior as an insulator/semiconductor type behavior. It was observed that the resistivity of the samples increased systemically with an increase of the NFO content. From the MR measurements, it was found that the MR effect is enhanced for x = 0.01 with a NFO composition. In all, the spin-polarized tunneling and the spin-dependent scattering may be beneficial for an improved low-field magnetoresistance effect. These phenomena can be explained by the segregation of a new phase related to NFO at the grain boundaries or surfaces of the LCMO grains.     

Synthetically Controlled,Carbon-Coated Co<Subscript>2</Subscript>SnO<Subscript>4</Subscript>/SnO<Subscript>2</Subscript> Composite Anode for Lithium-ion Batteries

The inherent drawbacks of Co₂SnO₄ in demonstrating the closer-to-theoretical capacity value behavior and the inadmissible volume-expansion-related capacity fade behavior have been surpassed by choosing a tailor-made material composition of Co₂SnO₄/SnO₂, prepared at two different temperatures such as 400°C and 600°C to obtain residual carbon-containing and carbon-free compositions, respectively. Among the products, carbon-coated Co₂SnO₄/SnO₂ composite exhibits better electrochemical performance compared with that of the carbon-free product mainly because of the beneficial effect of carbon in accommodating the volume-expansion-related issues arising from the alloying/de-alloying mechanism. A combination of conversion reaction and alloying/de-alloying mechanism is found to play a vital role in exhibiting closer-to-theoretical capacity values. In other words, an appreciable specific capacity value of 834 mAh g^?1 has been exhibited by Co₂SnO₄/SnO₂ anode containing carbon coating, thus, demonstrating the possibility to improve the electrochemical performance of the title anode through carbon coating, which is realized as a result of the addition of carefully manipulated synthesis conditions.     

Controllable Low-Temperature Hydrothermal Synthesis and Gas-Sensing Investigation of Crystalline SnO<Subscript>2</Subscript> Nanoparticles

SnO₂ nanoparticles have been successfully synthesized by a facile hydrothermal method from SnCl₂·2H₂O, hexamethylenetetramine, and trisodium citrate in water at 120 °C for 12 h. The effects of surfactant and precipitant on SnO₂ synthesis were investigated. SnO₂ nanoparticles can be synthesized in the temperature range of 120-180 °C with long reaction time in the presence of trisodium citrate. When NaOH was used as precipitant instead of hexamethylenetetramine, it is difficult to obtain SnO₂ nanoparticles at 120 °C in the presence of trisodium citrate. SnO₂ nanoparticles with an average size of about 5 nm show good crystallinity and excellent sensitivity to ethanol and acetaldehyde in about 55% relative humidity.     

Gas sensing properties of nano-crystalline SnO<Subscript>2</Subscript>-CuO compounds

We fabricated a micro gas sensor for hydrogen sulfide (H₂S) gas using MEMS technology and the sol-gel process, and synthesized SnO₂-CuO as a sensing material by the sol-gel method. Synthesized particles of SnO₂-CuO were characterized with an average particle size of about 40 nm as measured by FE-SEM imagery and XRD peaks. The sensing material was coated on the micro platform and annealed at 400 °C. The maximum gas sensitivity (R_s= R_g/R_a) was 0.005 at 300 °C for 1.0 ppm — H₂S. The gas sensitivity showed linear behavior with increasing H₂S concentration.     

Grain refinement and mechanism of CAl_（0.5）W_（0.5） compound in Mg-Al alloys

The effect of CAl0.5W0.5(CAW) compound on the grain refinement of Mg-Al based alloys was investigated.The results show that CAW compound is an effective and active grain refiner.The grain size of binary Mg-Al alloys is more than 500 μm,and it is changed to about 110 μm with a 1 wt.% CAW addition.The hardness increased with the decease of grain size monotonously.The mechanical properties are improved by the addition.The fine grain size is mainly ascribed to the dispersed Al2CO particles,which are very potent nucleating substrates for Mg-Al alloys.The nucleation cores formed by chemical reaction directly are well-distributed in the matrix.     

Experimental investigation and thermochemical assessment on the SnO<Subscript>2</Subscript>-CuO system

Differential thermal analysis/theromgravimetry (DTA/TG) measurements performed in air have established that above 1273 K the SnO₂-CuO initially stochiometric system transforms into a system of the SnO₂-CuO_x type, with the value of x depending on temperature T and p _{O 2} oxygen partial pressure values. The dissociation process of CuO to Cu₂O, as well as the formation of a liquid phase with an uptake of oxygen, has been experimentally verified. Above the minimum value of the oxygen partial pressure for which the only components of the system are SnO₂ and CuO (i. e., over p_{O 2} = 24 atm), the phase diagram was calculated by modeling the behavior of the liquid phase with a sub-regular approximation. A homogeneous liquid phase with no tendency toward immiscibility was found to be energetically favorable over the entire compositional range of the SnO₂-CuO system for T ≥ 1470 K. As a result of the calculations, the phase diagram is given for p_{O 2} = 24 atm; the diagram is a simple eutectic type with the eutectic composition placed in the CuO-rich domain (i.e., copper oxide molar fraction x = 0.873 and melting at 1470 K). The phase diagram calculated for the SnO₂-CuO system is compared with the data reported for other CuO-based systems.     

Effects of nano-TiO<Subscript>2</Subscript> dispersion on thermoelectric properties of Co<Subscript>4</Subscript>Sb<Subscript>11.7</Subscript>Te<Subscript>0.3</Subscript> composites

Nano-TiO2/Co4Sb11.7Te0.3 composites were prepared by mechanical alloying (MA) and cold isostatic pressing (CIP) process.The phase composition,microstructure,and thermoelectric properties were characterized.The diffraction spectra of all samples well corresponds to CoSb3 skutterudite diffraction plane.TiO2 agglomerates into irregular clusters.They locate at the grain boundaries or some are distributed on the surface of Co4Sb11.7Te0.3 particles.For composites with high TiO2 content (0.6% and 1.0% TiO2),the phonon scattering by TiO2 particle,pores,and small size grains can result in a remarkable reduction in thermal conductivity.The maximum value of ZT is 0.79 for sample with 0.6 wt.% TiO2 at 700 K,which is 11% higher than that of non-dispersed sample.     

Suspension Plasma-Sprayed ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanostructured Coatings for ppm-Level Acetone Detection

Zinc ferrite (ZnFe₂O₄) sensitive coatings have been deposited by suspension plasma spraying. The phase constitution of the coatings was characterized by x-ray diffraction while the top surface and cross-sectional morphology of the coatings were inspected by scanning electron microscopy. The response to acetone was tested with the concentration in the range of 25-500 ppm at the working temperature from 175 to 275 °C. The sensors that were deposited at an arc current of 400 A showed better performance than those at 600 A owing to small grain size and high porosity. The sensor response increased with acetone concentration. The optimized sensors showed excellent response/recovery time and selectivity to acetone at 200 °C.     

NO2 gas sensing based on ordered ultrathin films of conducting polymer and its nanocomposite

The metal oxides films are widely used for CO, aromatic hydrocarbon and NO₂, gas-sensing applications, but such sensors mostly lack selectivity and operate at high temperatures (300–500 °C). We focused on the use of organized ultrathin films of conducting polymers and their nanocomposites, which recognize selectively the NO₂ gases with a very high sensitivity (≤ppb). Polyhexylthiophene (PHTh), poly(ethylene dioxythiophene) (PEDT), PHTh–PEDT copolymer, sulfonated polyaniline, polyaniline (PANI)–SnO₂, polypyrrole (PPy)–SnO₂, PEDT-SnO₂, PHTh–SnO₂ and copolymer (HTh-EDT)–SnO₂ conducting polymer and nanocomposite thin films were fabricated and used for gas sensing applications. The physical properties (UV and FTIR) such films were investigated before and after the NO₂ gas treatment. Regioregular PHTh, its copolymer P(HTh-PEDT), and their metal oxide nanocomposites films detected NO₂ gas with a high sensitivity.     

Preparation and electrocatalytic property of Au-Pt/SnO<Subscript>2</Subscript>/GC composite electrode

Au-Pt/SnO₂/GC composite electrode was prepared by self-assembling Au-Pt nanoparticles on SnO₂ film, which was deposited on actived glassy carbon (GC). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images revealed that dense and uniform Au-Pt particles with 25-nm diameter were dispersed on SnO₂ film. X-ray photoelectron spectroscopy (XPS) results proved that there was an interaction between Au-Pt nanoparticles and SnO₂ support. Electrochemical experiments showed that Au-Pt/SnO₂/GC composite electrode had a good electrocatalytic activity to the oxidation of methanol.     

Preparation and microstructure characterization of a nano-sized Ti<Superscript>4+</Superscript>-doped AgSnO<Subscript>2</Subscript> electrical contact material

A Ti⁴⁺-doped nano-structured AgSnO₂ material was prepared using sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results show that Ti⁴⁺ cations are successfully doped into the crystal lattice of SnO₂, and thus significantly improve the electrical conductivity of the sample. Furthermore, the coating of Ag on Ti⁴⁺-doped SnO₂ nano-sized particles enhances the surface wettability and enables the resulting AgSnO₂ material to have better mechanical properties.     

Template-free hydrothermal synthesis of single-crystalline SnO<Subscript>2</Subscript> nanocauliflowers and their optical properties

Large-scale single-crystalline SnO₂ nanocauliflowers were successfully synthesized using a hydrothermal growth method without any template. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). FE-SEM images show that the as-grown SnO₂ nanocauliflowers are constructed of tetragonal prisms with a width of 500–600 nm. XRD, EDS, and SAED results indicate that the as-grown SnO₂ nanocauliflowers are single crystalline with the tetragonal rutile crystalline structure. The growth mechanism of SnO₂ nanocauliflowers is also preliminarily discussed on the basis of different Sn(OH)₆²⁻ concentrations, and it is found that Sn(OH)₆²⁻ concentration plays an important role in determining the shape of the prepared SnO₂. Room temperature photoluminescence was further carried out on SnO₂ nanocauliflowers to investigate their optical properties. An intense blue luminescence centered at a wavelength of 424 nm is observed in the as-grown SnO₂ nanocauliflowers.     

Capacitance performance enhancement of TiO<Subscript>2</Subscript> doped with Ni and graphite

Nano-amorphous TiO₂ was prepared by a sol-gel method. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the composite electrode material (TiO₂-NiO-C) is made of powder with a grain size of 36.2 nm. Doping of nickel and graphite can increase the electrical conductivity and the specific surface area of nano-amorphous TiO₂. The electrochemical properties of TiO₂-NiO-C, such as self-discharge, leakage current, and cycle life, were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge test. With a charge-discharge current density of 500 mA/g, the specific capacity of the TiO₂-NiO-C composite material reaches 12.88 mAh/g. Also, the expense of capacity is only 3.88% after 500 cycles. The electrochemical capacitor with the electrode material of TiO₂-NiO-C shows excellent capacity and cycling performance.     

碳纳米管修饰的空心多孔NiO/SnO2纳米复合材料对丙酮传感性能的优化

通过静电纺丝法制备中空多孔的NiO/SnO2复合纳米纤维,在复合纤维表面装饰碳纳米管,在此基础上制备气敏传感器器件。利用TGA确定了复合材料热分解温度,得到热处理工艺;利用SEM、XRD、TEM、XPS分别对复合材料的形貌、结构、尺寸、表面成分进行了表征。使用WS-30A气敏元件测试仪对气敏元件响应进行测试,结果表明CNTs装饰的NiO/SnO2复合纳米材料制备的气敏传感器降低了丙酮检测最佳工作温度,为160℃,提高了检测灵敏度,对50 ppm丙酮的响应达到25.25,对检测丙酮有快速的响应(~8.2 s)以及恢复性能(~10.5 s),同时在30天的长期稳定性测试中也体现了良好的稳定性。证明了装饰CNTs 的 NiO/SnO₂复合材料在检测丙酮方面的潜在价值,同时本文也进一步讨论了CNTs, 中空多孔结构的NiO/SnO₂提高检测性能的作用机理。     

Electronic structures of Heusler alloy Co2FeAl1-xSix surface

We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) be-come close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.     

The role of Ce ions in electrochemical corrosion of 304 SS in Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>.6H<Subscript>2</Subscript>O

Effects of temperature and potential on the electrochemical corrosion behavior of alloy AISI 304 (UNS S30400) Stainless steel were investigated in 3 wt.% cerium nitrate (Ce[NO₃]₃.6H₂O) solution. With an increase in electrolyte temperature from ambient temperature to 90°C, the corrosion potential of the alloy shifted towards the noble direction, and the resistance to polarization increased due to the formation of Ce-oxide on the electrode surface. The oxide films formed at the open circuit potential (OCP) and a passive potential of 0.4 V_SCE were examined by x-ray photoelectron spectroscopy (XPS). The oxide film formed at 50°C and a passive potentialof 0.4 V_SCE consists of mixed oxides of Ce and Cr, whereas that at OCP consists of only Cr oxide. The formation of Cr oxides on the electrode surface was primarily due to the nitrate (NO₃ ⁻) ions in Ce(NO₃)₃.6H₂O electrolyte.     

Phase Diagram of the Quaternary Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-Zn(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O System

The phase diagram of the H₂O-Zn(NO₃)₂-Al(NO₃)₃-Cu(NO₃)₂ quaternary system at 30 °C has been established by using the conductivity measurements. The solid-liquid equilibria of the H₂O-Zn(NO₃)₂-Al(NO₃)₃, H₂O-Zn(NO₃)₂-Cu(NO₃)₂, H₂O-Al(NO₃)₃-Cu(NO₃)₂ ternary systems and two isoplethic sections were determined experimentally. The solid phases in equilibrium with the saturated solution are the tri- and hemipentahydrate of copper nitrate, the hexahydrate α and β of the zinc nitrate and the nonahydrate of aluminum nitrate. The copper and zinc nitrates are relatively soluble in opposition to the aluminum nitrate which presents some important precipitation domains.     

Preparation and optical properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> powder

Y(NO3)3 and NH3·H2O were used as a raw materials,and nano-Y2O3 powder was successfully synthesized by a precipitation method.Employing TEOS as a raw material,SiO2 powder was successfully prepared by a alkoxide-hydrolysis method,and a Y2O3/SiO2 composite powder was obtained by coating.The Y2O3,SiO2,and Y2O3/SiO2 powders were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),and Fourier transform infrared spectrophotometer(FT-IR);the Y2O3 and Y2O3/SiO2 powders were further examined ...     

Enhancement of room-temperature magnetoresistance in La<Subscript>0.6</Subscript>Dy<Subscript>0.1</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The samples of La0.6Dy0.1Sr0.3MnO3/(Ag2O)x/2(x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.25, and 0.30) were prepared by using the solid-state reaction method.Their magnetic property, transport behavior, transport mechanism and magnetoresistance effect were studied through the measurements of magnetization-temperature(M-T) curves, ρ-T curves and the fitting of ρ-T curves.The results indicated that Ag could take part in the reaction when the doping amount is small.However, when the doping amount is compar...