Sol–gel template synthesis of LiV<Subscript>3</Subscript>O<Subscript>8</Subscript> nanowires

The LiV₃O₈ nanowires are fabricated by using sol–gel process with porous anodic aluminum oxide (AAO) as the template. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) characterizations show that the synthesized LiV₃O₈ nanowires are monodispersed and paralleled to one another. Selected area electron diffraction (SAED) pattern, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) investigations jointly demonstrate that the synthesized nanowires are most consisted of monoclinic phase LiV₃O₈. Since the LiV₃O₈ nanowires can be mass-produced by using this method, it is expected to find promising application as a new cathode material in lithium ion battery.     

The synthesis of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> nanobelts by vapor–liquid–solid method and their electrical transport properties

Bi₂Te₃ nanobelts were synthesized on quartz substrates by gold-mediated vapor–liquid–solid (VLS) growth through a thermal evaporation process. The structure and morphology were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The temperature dependence of the conductivity of Bi₂Te₃ single crystal nanobelt shows a semiconductor behavior, and the activation energy was calculated as about 25 meV, indicating that the thermal activation of carriers from the impurity level dominates the transport property.     

In‐situ Observations of Nanoscale Effects in Germanium Nanowire Growth with Ternary Eutectic Alloys

Vapour‐liquid‐solid (VLS) techniques are popular routes for the scalable synthesis of semiconductor nanowires. In this article, in‐situ electron microscopy is used to correlate the equilibrium content of ternary (Au_0.75Ag_0.25–Ge and Au_0.65Ag_0.35–Ge) metastable alloys with the kinetics, thermodynamics and diameter of Ge nanowires grown via a VLS mechanism. The shape and geometry of the heterogeneous interfaces between the liquid eutectic and solid Ge nanowires varies as a function of nanowire diameter and eutectic alloy composition. The behaviour of the faceted heterogeneous liquid–solid interface correlates with the growth kinetics of the nanowires, where the main growth facet at the solid nanowire–liquid catalyst drop contact line lengthens for faster nanowire growth kinetics. Pronounced diameter dependent growth kinetics, as inferred from liquid–solid interfacial behaviour, is apparent for the synthesised nanowires. Direct in‐situ microscopy observations facilitates the comparison between the nanowire growth behaviour from ternary (Au–Ag–Ge) and binary (Au–Ge) eutectic systems.     

Fabrication and magnetic properties of Fe<Subscript>3</Subscript>Co<Subscript>7</Subscript> alloy nanowire arrays

Fe₃Co₇ alloy nanowire arrays have been fabricated by direct current electrodeposition of Fe²⁺ and Co²⁺ into anodic aluminum oxide (AAO) templates. The phase structure and magnetic properties of the nanowires were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Magnetic measurements show that the coercivity and remanence of the as-deposited Fe₃Co₇ Alloy nanowires increase dramatically after heat-treatment at 773 K for 2 h, and the nanowire arrays exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. The great difference between practical coercivity and ideal coercivity was also discussed in detail.     

Temperature dependent growth and optical properties of SnO<Subscript>2</Subscript> nanowires and nanobelts

SnO₂ nanowires and nanobelts have been grown by the thermal evaporation of Sn powders. The growth of nanowires and nanobelts has been investigated at different temperatures (750–1000°C). The field emission scanning electron microscopic and transmission electron microscopic studies revealed the growth of nanowires and nano-belts at different growth temperatures. The growth mechanisms of the formation of the nanostructures have also been discussed. X-ray diffraction patterns showed that the nanowires and nanobelts are highly crystalline with tetragonal rutile phase. UV-visible absorption spectrum showed the bulk bandgap value (∼ 3–6 eV) of SnO₂. Photoluminescence spectra demonstrated a Stokes-shifted emission in the wavelength range 558–588 nm. The Raman and Fourier transform infrared spectra revealed the formation of stoichiometric SnO₂ at different growth temperatures.     

Splitting behavior and structural transformation process of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> whiskers under hydrothermal conditions

The splitting behavior and structural transformation process of K₂Ti₆O₁₃ whiskers in various hydrothermal solutions were investigated by the X-ray diffraction technique, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. TiO₂ (B) particle aggregates and rutile twinned crystals were produced respectively in diluted and concentrated HCl solutions via “dissolution-precipitation” mechanism, while no changes were observed in deionized water. In contrary to the chemical inertia of K₂Ti₆O₁₃ whiskers in KOH solution, trititanate nanowires were synthesized by splitting the bulk K₂Ti₆O₁₃ whiskers in NaOH solution. The driving force for the formation of nanowires originated from the intrinsic strain induced by the phase transition from K₂Ti₆O₁₃ with a tunnel structure to layered trititanate. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural,optical, and opto-dielectric properties of W-doped Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

A layer-by-layer deposition technique of Ga₂O₃ and WO₃ by vacuum evaporation method on glass and silicon substrates and subsequent annealing in oxygen atmosphere to form W-doped Ga₂O₃ (or Ga₂O₃:W) films was attempted here. The W doping level was measured by the energy dispersive X-ray fluorescence radiographic analysis. The crystalline structure of Ga₂O₃:W films was determined by the X-ray diffraction method. Experimental data indicate that W⁶⁺ ions doped in host Ga₂O₃ forming solid solutions (SS), in which the molar ratio (r) of W to Ga is 9.6, 13.4, 18.2, 22.7 and 30.4%. All the prepared SS have the known β-Ga₂O₃ crystalline structure. This doping controls the optical and electrical properties of the host Ga₂O₃. The optical properties of the prepared Ga₂O₃:W films were studied by UV–VIS–NIR absorption spectroscopy method from which the bandgap was determined. In general, it was found that the prepared Ga₂O₃:W films are wide-bandgap semiconductors with bandgap 4.69–4.47 eV and have dielectric properties. The optical sensitivity of the capacitance, dissipation factor and ac-conductance of the Ga₂O₃:W films grown on Si was studied as a function of W-doping level. It was observed that the prepared Ga₂O₃:W film of r = 22.7% has the highest photosensitivity amongst the other samples.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

TEM and HAADF-STEM study of the structure of Au nano-particles on CeO<Subscript>2</Subscript>

The structure and growth process of Au particles on CeO₂ were observed by the transmission electron microscope (TEM) equipped with the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) system. The growth of Au particles on CeO₂ was shown to be mainly Ostwald ripening under heating at various temperatures, although it is suppressed in the hydrogen atmosphere. In the HAADF-STEM observation of Au/CeO₂ interfaces with the orientation relationship of (111)[1–10]Au//(111)[1–10]CeO₂, (111)[−110]Au//(111)[1–10]CeO₂ and atomic columns of Au and Ce were successfully resolved, and the interface structure was analyzed in details for the first time.     

Synthesis of In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanomaterials incorporating Au

In(OH)₃ and In₂O₃ nanocrystals of rectangular shape and incorporating Au were synthesized with a hydrothermal process and thermal decomposition. Powder X-ray diffraction, electron microscopy (SEM, TEM), and energy-dispersive spectroscopy studies reveal that elemental Au nanoparticles are dispersed on the surface of In(OH)₃ rectangular nanocrystals and incorporated into In₂O₃ nanoporous particles. UV–vis spectral measurements reveal a surface-enchanced plasma band near λ ~532 nm for both Au-incorporating nanomaterials. The BET surface areas of Au-incorporating In(OH)₃ and In₂O₃ are 26.2 and 35.5 m²/g, respectively. The incorporation of elemental Au in In(OH)₃ and In₂O₃ nanomaterials is attractive for sensor, catalyst and solar-cell applications.     

Visible-light activities of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>/BiVO<Subscript>4</Subscript> composite photocatalysts

Gd₂O₃/BiVO₄ composite photocatalysts were hydrothermal synthesized and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and UV–vis diffusion reflectance spectra; all the composite photocatalysts exhibited enhanced photocatalytic activities than the pure BiVO₄ for degradation of methyl orange under visible-light irradiation. The improved activity of composites was discussed and ascribed to the electron-scavenging effect of dopants.     

Preparation and characterisation of nanostructural TiO<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> binary oxides with high surface area derived form particulate sol–gel route

Nanostructured and nanoporous TiO₂–Ga₂O₃ films and powders with various Ti:Ga atomic ratios and high specific surface area (SSA) have been prepared by a new straightforward particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate were used as precursors and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the SSA. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that powders contained both rhombohedral α-Ga₂O₃ and monoclinic β-Ga₂O₃ phases, as well as anatase and rutile. It was observed that the Ga₂O₃ formed from the nitrate precursor retarded anatase-to-rutile transformation. Furthermore, transmission electron microscope (TEM) analysis also showed that Ga₂O₃ hindered the crystallisation and crystal growth of powders. SSA of powders, as measured by Brunauer–Emmett–Teller (BET) analysis, was enhanced by introducing Ga₂O₃. Ti:Ga = 50:50 (at%/at%) binary oxide annealed at 500 °C produced the smallest crystallite size (2 nm), the smallest grain size (18 nm), the highest SSA (327.8 m²/g) and the highest roughness. Ti:Ga = 25:75 (at%/at%) annealed at 800 °C showed the smallest crystallite size (2.4 nm) with 32 nm average grain size and 40.8 m²/g surface area. Ti:Ga = 75:25 (at%/at%) annealed at 800 °C had the highest SSA (57.4 m²/g) with 4.4 nm average crystallite size and 32 nm average grain size. One of the smallest crystallite size and one of the highest SSA reported in the literature is obtained, and they can be used in many applications in areas from optical electronics to gas sensors.     

Room-Temperature Photomagnetic Effect of Fe<Subscript>3</Subscript>Ga<Subscript>4</Subscript> Grown on GaAs Substrates

Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of [100-nm GaAs/50-nm Fe₃Ga_{2− x} As _x /100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals the formation of metamagnetic Fe₃Ga₄ grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T _N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition with the enhancement due to the light-induced heating.     

Electrical and magnetic properties of (BiNa)<Subscript>1/2</Subscript>(FeV)<Subscript>1/2</Subscript>O<Subscript>3</Subscript>

Potential multiferroic material, (BiNa)_1/2(FeV)_1/2O₃, synthesized using solid-state route is investigated. The phase formation was confirmed by X-ray diffraction and surface morphology by scanning electron microscopy (SEM). Structural data reveal the single phase formation corroborated by SEM. The grain distribution is uniform with an average grain size of 3·6 μm. Electrical properties were investigated in a frequency range (1 kHz–1 MHz) by complex impedance spectroscopy (CIS) technique. The material showed negative temperature coefficient of resistance (NTCR) reflecting semiconductor behaviour. A.C. conductivity was found to obey Johnscher’s law. Conductivity mechanism is discussed and activation energy estimated (1·17 eV) for the conduction process is associated with Fe^3 +→ Fe^2 + variable state. The M–H curve showed the presence of ferromagnetism in the studied material.     

The influence of the cooling rate on bulk metallic glass formation in Mg<Subscript>80</Subscript>Cu<Subscript>15</Subscript>Y<Subscript>5</Subscript> and Mg<Subscript>80</Subscript>Cu<Subscript>10</Subscript>Y<Subscript>10</Subscript>

The Mg–Cu–Y system is known to be one of the best glass formers among the various existing magnesium alloys. The compositions chosen for the current study were Mg₈₀Cu₁₅Y₅ and Mg₈₀Cu₁₀Y₁₀. Different casting processes yielded four different microstructures that were analyzed by means of X-ray diffraction, scanning electron microscopy, high resolution scanning electron microscopy, and energy-dispersive X-ray spectroscopy chemical analysis. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mold held at different temperatures (cooled to −195 °C with the aid of liquid nitrogen, held at room temperature and heated up to 300 °C) and melt-spinning. Detailed microstructure study was then performed on the melt-spun specimen using transmission electron microscopy and high resolution transmission electron microscopy. The above-mentioned investigation revealed a crystalline rather than amorphous structure. The observed microstructure could not be explained on the basis of current models referring to the frequency of nucleation events.     

Template synthesis of BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> ordered nanowire arrays by a new method

A method that the precursor is generated in situ and shaped into the one dimension nanostructure in the nanochannels of the anodic alumina membrane (AAM) template is described. The high-aspect ratio nanowire array of the BaFe₁₂O₁₉ was prepared by means of this method. Electron microscope images showed that the BaFe₁₂O₁₉ nanowire array was abundant, uniformly distributed and well-ordered in the large area. It is estimated from the electron microscope images that the diameter of the individual nanowire is about 60 nm and the length was corresponding to the thickness of the applied AAM template. The analysis of X-ray diffraction demonstrated that the BaFe₁₂O₁₉ nanowires have a hexagonal structure of the pure phase BaFe₁₂O₁₉.     

Formation,thermal, optical and physical properties of GeS<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–AgCl novel chalcohalide glasses

Novel GeS₂–Ga₂S₃–AgCl chalcohalide glasses had been prepared by melt-quenching technique, and the glass-forming region was determined by XRD, which indicated that the maximum of dissolvable AgCl was up to 65 mol%. Thermal and optical properties of the glasses were studied by differential scanning calorimetry (DSC) and Visible-IR transmission, which showed that most of GeS₂–Ga₂S₃–AgCl glasses had strong glass-forming ability and broad region of transmission (about 0.45–12.5 μm). With the addition of AgCl, the glass transition temperature, Tg decreases distinctly, and the short-wavelength cut-off edge (λ_vis) of the glasses also shifts to the long wavelength gradually. However, the glass-forming ability of the glass has a complicated evolutional trend depended on the compositional change. In addition, the values of the Vickers microhardness, H _v , which decrease with the addition of AgCl, are high enough for the practical applications. These excellent properties of GeS₂–Ga₂S₃–AgCl glasses make them potentially applied in the optoelectronic field, such as all-optical switch, etc.     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

Physicochemical properties of La<Subscript>3</Subscript>Ga<Subscript>5.5</Subscript>Ta<Subscript>0.5</Subscript>O<Subscript>14</Subscript>

We report the optical and dielectric properties and microhardness of La₃Ga_5.5Ta_0.5O₁₄ lanthanum gallium tantalate (langatate) crystals. Analysis of the optical transmission spectra of the crystals in relation to their refined compositions indicates that the bands at 34000–35000 and 27000–28000 cm⁻¹ are due to lanthanum and oxygen vacancies, respectively, and that the band at 20000–21000 cm⁻¹ is responsible for the yellow (orange) coloration of the crystals. Their resistivity and microhardness decrease with increasing oxygen vacancy concentration.     

Role of Ti diffusion on the formation of phases in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> brazed interface

Diffusivities of Ti, Cu, Al and Ag in the interface of Al₂O₃–Al₂O₃ braze joints using Ag–Cu–Ti active filler alloy, have been calculated by Matano–Boltzman method. The Matano plane has been identified for each elemental diffusion at various brazing temperatures. The diffusivities of Ag, Cu and Al are almost insignificant on formation of interface during brazing, whereas the diffusivity of Ti changes significantly with the brazing temperature and controls the formation of different reaction product in the interface. Presence of TiO and Ti₃Cu₃O phases in the interface has been confirmed by transmission electron microscopy (TEM).