Structure, electrochromic and optical properties of WO3 film prepared by dip coating-pyrolysis

The tungsten oxide (WO₃) film was grown by dip coating-pyrolysis method with the PEG-400 as the structure-directing agent. Microstructure of the WO₃ film was characterized by TG-DSC, XRD and SEM techniques. It was found that the film annealed at 350 °C for 2 h comprised cubic WO₃ and orthorhombic WO₃. The measurements of the cyclic voltammetry (CV) and UV-vis spectrum suggested that the WO₃ film had a good electrochromic reversibility performance. The film possessed excellent modulation to the visible light and the maximal average transmittance modulation reached 70.06%.     

Investigation on structural characteristics of PVDF–AgCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite solid polymer electrolyte system

There has been an increasing interest towards the incorporation of nanosize ceramic fillers in polymer electrolytes. Solid polymer electrolytes based on polyvinylidene fluoride (PVDF), silver triflate (AgCF₃SO₃), and x wt% of aluminum oxide (Al₂O₃) nanopowders (where x = 1, 3, 5, and 10, respectively) have been prepared using solution casting technique. The structural characteristics of these thin film specimens were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) patterns at room temperature. The appearance of new absorption bands and gradual shifts observed in some characteristic peaks confirmed the complex formation between polyvinylidene fluoride and silver triflate. Furthermore, the addition of nanosized filler Al₂O₃ has also indicated the interaction of the filler with the polymer salt complex. The XRD patterns obtained for all these samples in the 2θ range 10° to 70° showed the amorphous nature of these samples. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Preparation of TiO<Subscript>2</Subscript>-coated LiCo<Subscript>1/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by electrostatic self-assembly method and its properties

A precursor of TiO₂–LiCo_1/3Ni_1/3Mn_1/3O₂ was prepared by electrostatic self-assembly method. The final product was obtained by heating the precursor at 400–450 °C for 4–6 h in air. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests were used to examine the structural, morphology, elementary valence, and electrochemical characteristics. XRD indicated that the TiO₂-coated material can be indexed by α-NaFeO₂ layered structure, which belongs to hexagonal-type space group R3m. XPS results confirmed the existence of TiO₂ compound on the surface of the coated sample. The SEM image showed that the material had spherically porous morphology with the uniform size about 6 μm. The initial charge–discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ material was 168.8/160.0 mAh/g. After 60 cycles, the discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ sample was 147.0 mAh/g, and the coulombic efficiency was 94.0%. Compared with the uncoated sample, the electrochemical performance of TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was improved.     

Preparation of nanosized Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> using different content of starting materials and their photoactivities

A series of nanosized Bi₂WO₆ catalysts was synthesized using various starting materials, and they were characterized by X-ray diffractometry, transmission electron microscopy, and diffuse reflectance spectroscopy. Rhodamine-B (RhB) photodegradation in aqueous medium was employed as a probe reaction to test the photoactivity of the as-prepared samples. Dependence of the photocatalytic activities on different contents of the starting materials was examined under visible irradiation (λ > 400 nm). The sample prepared in the following conditions: reaction time 24 h, the pH of the solution 7, the Bi³⁺ amount in the start precipitates 5 mmol — exhibited the highest photochemical activity when the hydrothermal temperature was settled at 180°C. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 243–249, Martch–April, 2009.     

Cells studies on PEO/PEG/NaClO<Subscript>3</Subscript> thin-film electrolyte system based on composite V<Subscript>2</Subscript>O<Subscript>5</Subscript> electrode

The thin-film solid polymer electrolyte based on polyethylene oxide (PEO) with sodium chlorite (NaClO₃) has been prepared by a solution-cast technique. The electrolyte was characterized by X-ray diffraction (XRD), infrared (IR), cyclic voltammetry, alternating current conductivity, and Wagner’s polarization studies. The complexation of NaClO₃ with PEO was confirmed through the XRD and IR studies. The transference number measurement has shown that the ion transport is predominant over electrons in the polymer electrolytes (t _ions ≈ 0.94). The conductivity enhancement was observed in the case of the PEO/NaClO₃ system with the addition of plasticizers (low-molecular-weight polyethylene glycol, organic solvents propylene carbonate and dimethyl formamide. Cyclic voltammetry analysis showed the stability and redox character of the electrolyte and electrode. Finally, polymer electrolyte systems were examined by electrochemical cell studies using V₂O₅ and composite V₂O₅ cathode at temperature of 35 °C. Overall, the plasticized electrolyte shows a better electrochemical performance, and a higher discharge capacity was observed in composite V₂O₅-based cells over V₂O₅-based cells.     

Synthesis of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al₂O₃ substrate, ZnAl₂O₄/α-Al₂O₃ complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl₂O₄ changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl₂O₄ transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present that ZnAl₂O₄ prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl₂O₄/α-Al₂O₃ substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl₂O₄ layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl₂O₄ layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film.     

Effect of annealing time on properties of spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> high-voltage lithium-ion battery electrode materials prepared by co-precipitation method

In this wok, a series of LiNi_0.5Mn_1.5O₄ (LNMO) samples with an octahedral shape entirely composed of (111) crystal planes were prepared by calcining the mixture of the precursor Ni_0.25Mn_0.75(OH)₂ and LiOH·H₂O at 800 °C for 15 h in air, followed by annealing them at 600 °C for different dwelling times. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and several electrochemical technologies were used to investigate the effect of annealing time on properties of the LNMO samples. XRD analysis indicates that the lattice parameters of the LNMO samples show a decreasing trend with increasing of annealing time, and the impurity peaks become less apparent for the sample annealed for 6 h and almost disappear for the samples annealed for 9 and 24 h. SEM results show that the annealing time has no obvious influence on the morphologies of the LNMO samples. Electrochemical measurements show that the electrochemical performances (capacity, cycle life, and rate capability) of the samples annealed for 6, 9, and 24 h are better than those of the unannealed sample, and the sample annealed for 9 h shows the best electrochemical properties among them due to its superior electrochemical kinetics of Li⁺ insertion/desertion.     

Ultrasound-assisted dispersion of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanoparticles in organic solvents and the use of the dispersion as magnetic cosmetics

A new method of dispersing the aggregated strontium hexaferrite (SrFe₁₂O₁₉) magnetic nanoparticles in organic solvents such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol (PG), and glycerol, by an ultrasonic bath is reported herein. The particles size of SrFe₁₂O₁₉ after treatment with the PGMEA is in the range 70–100 nm. The structure of dispersed SrFe₁₂O₁₉ was characterized using transmission electron microscopy (TEM), high resolution scanning electron microscopy (HR SEM) and thermo gravimetric analysis (TGA). This dispersed material was used for the preparation of a topical magnetic cosmetic product as follows: The dispersion of SrFe₁₂O₁₉ in PG was mixed with “Dermud-Ahava Body Cream”, an ‘oil in water’ emulsion of a Dead Sea mineral cosmetic, “AHAVA”, and the magnetic properties of the created composite were determined. The ferrimagnetic behavior of the composite has been demonstrated as being very similar to the behavior of strontium hexaferrite itself.     

CoMoS<Subscript>4</Subscript> Nanoflowers as Anode for Secondary Lithium Batteries

CoMoS₄ nanoflowers was synthesized by precipitation method from Na₂MoO₄, CoCl₂ · 6H₂O and CH₃CSNH₂ as starting materials. X-ray diffraction (XRD) analysis showed that the prepared samples is amorphous structure, X-ray photoelectron spectrometer data of Co, Mo and S in CoMoS₄ revealed that the valences of the corresponding elements are almost +2, +6, and −2, respectively. Scanning electron microscope gave the result that the morphologies of the as-prepared powder is flower-like nanostructure. Moreover, electrochemical tests were also carried out, the initial discharge was 1547 mA h g⁻¹, even after 20 cycles, it still remains 461 mA h g⁻¹.     

Porous WO3 from anodized sputtered tungsten thin films for NO2 detection

In this paper, porous WO₃ films were prepared by anodic oxidation of metallic tungsten (W) films deposited on alumina substrates. The structural and morphological properties of the porous WO₃ films were investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). A large number of cracks appeared on the surface of films after anodization, which makes the films porous. The porous WO₃ sensors achieved their maximum response values to NO₂ at a low operating temperature of 150 °C. The porous WO₃ sensors showed high response values, great stability and fast response-recovery characteristics to different concentration of NO₂ gas due to the high specific surface area and special structural and morphological properties.     

Synthesis of the chain-shaped carbon fibers decorated with SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> beads by chemical vapor deposition

Chain-shaped carbon fibers decorated with SiO _x beads had been synthesized by using methyltriehlorosilane and normal carbon fibers as the raw materials, during which the chemical vapor deposition technique was applied. The products were characterized by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD) and Raman spectroscopy. The as-received products show chain-shaped morphologies that have the normal carbon fibers as “strings” and possess regular SiO _x beads of 30–40 μm with relative smooth surface. The formation of the chain-shaped morphology is considered to involve the shrinkage of the absorbed silica layer and the possible growth mechanism is further proposed. It is thought that the chain-shaped carbon fibers are formed by two main stages.     

Growth and sintering effects of hydrated polycrystalline Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>

Polycrystalline Li₂WO₄ was sintered at temperatures, 400, 450, 500, 550, 600, 650, and 700 °C. After sintering at each particular temperature, the Li₂WO₄ was cooled to room temperature. The X-ray diffraction pattern of Li₂WO₄ exhibits dominant peaks attributable to 7Li₂WO₄.4H₂O (cubic) and Li₂WO₄ (hexagonal) and thus reveals the extent of hydration of the material. The composition varies on heating at several temperatures as shown by the presence of new peaks in the diffractogram. Thermogravimetric analysis is used to correlate respective structural and thermal properties in variation. The impedance spectra show the presence of a semicircle in the higher frequency regions and straight line behaviors at lower frequencies. SEM micrographs depict the image of sintered Li₂WO₄. Grain growth studies reveal the sensitiveness of grain toward temperature. The maximum grain size is observed to be ≈5.7 μm at 700 °C.     

Structural investigation on PEO-based polymer electrolytes dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF₃SO₃) dispersed with various concentrations of aluminum oxide (Al₂O₃) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte. The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T _g) whereas the degree of crystallization (X _c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of all these samples has revealed the presence of absorption bands around 1,000 cm⁻¹; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity thereby revealing that the significant contribution to electrical conduction was due to ions only. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006     

Effect of oxygen partial pressure and VO<Subscript>2</Subscript> content on hexagonal WO<Subscript>3</Subscript> thin films synthesized by pulsed laser deposition technique

We report on the effect of oxygen partial pressure and vacuum annealing on structural and optical properties of pulsed laser-deposited nanocrystalline WO₃ thin films. XRD results show the hexagonal phase of deposited WO₃ thin films. The crystallite size was observed to increase with increase in oxygen partial pressure. Vacuum annealing changed the transparent as-deposited WO₃ thin film to deep shade of blue color which increases the optical absorption of the film. The origin of this blue color could be due to the presence of oxygen vacancies associated with tungsten ions in lower oxidation states. In addition, the effects of VO₂ content on structural, electrochemical, and optical properties of (WO₃)_1−x (VO₂) _x nanocomposite thin films have also been systematically investigated. Cyclic voltammogram exhibits a modification with the appearance of an extra cathodic peak for VO₂–WO₃ thin film electrode with higher VO₂ content (x ≥ 0.2). Increase of VO₂ content in (WO₃)_1−x (VO₂) _x films leads to red shift in optical band gap.     

Solid state synthesis of nonstoichiometric Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> composites as visible-light photocatalyst

Nonstoichiometric Bi₂WO₆ photocatalyst with the composition of Bi_2?+?x WO_6?+?1.5x (?0.25 ≤ x ≤ 1) wa synthesized by a facile solid state reaction method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The Bi_2.5WO_6.75 photocatalyst showed excellent visible-light-driven photocatalytic performance; nearly 100 % of RhB (10 ppm, pH?=?3?~?4) was decomposed within 25 min, which demonstrated that nonstoichiometric semiconductors could be an efficient visible-light-driven photocatalyst.     

Synthesis of Yb-doped Ba(Ce,Zr)O3 ceramic powders by sol–gel method

This study was aimed to synthesize a ceramic electrolyte of BaCe_0.76Zr_0.19Yb_0.05O_2.975 using acetate and chloride precursors. The transparent sol was stable for more than 10 months but only 3 months for the gel. The dried gel was characterized using thermogravimetric analysis/differential scanning calorimetry, particle analyzer, X-ray diffraction (XRD), and scanning electron microscopy/dispersive X-ray (SEM/EDX) analysis. Thermal behavior analysis showed three steps of weight losses. All the processes were exothermic reactions as shown by derivative thermogravimetric analysis signal. Two groups of particle size were observed in the particle size distribution for the sample in the form of sol and powders ranging from 100 to 1,100 nm. A high purity single-phase sample with orthorhombic structure was identified by XRD. The theoretical density estimated from the unit cell parameters was 6.40 g cm⁻³. SEM of the powdered sample showed homogeneous distribution of particles and the grains size were in the range of 0.7–1.3 μm. EDX data revealed that the residue of small amount of chloride (≈0.25%) was still present in the final product of the compound.     

Hydrogen gas-sensing properties of Pt/WO<Subscript>3</Subscript> thin film in various measurement conditions

A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO₃). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO₃ thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO₃ thin films prepared at 400 °C showed the largest change in optical transmittance and electrical conductivity when exposed to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance of W⁵⁺ in the thin films depend on the equilibrium reaction between injection and rejection of H⁺ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations.     

Synthesis and characterization of electron beam evaporated LiCoO<Subscript>2</Subscript> thin films

LiCoO₂ thin films were prepared by electron beam evaporation technique using LiCoO₂ target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10⁻⁴ mbar. The films prepared at substrate temperature T _s < 573 K were amorphous in nature, and the films prepared at T _s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–e_g absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t_2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006     

Sputtering deposition and characterization of Ru-doped WO3 thin films for electrochromic applications

Mixed tungsten-ruthenium oxide thin films were prepared for the first time by dc magnetron co-sputtering technique and were studied by cyclic voltammetry, optical transmission measurements, Raman spectroscopy and the W L₃ and Ru K edges X-ray absorption spectroscopy (XAS) in comparison with pure WO₃ films. The Ru concentration was varied in the range from 0 to 28 at.%. XAS results suggest that the average local structure around both tungsten and ruthenium ions remains unchanged within experimental accuracy in all samples, moreover, for tungsten ions, it resembles that of pure WO₃ films. However, the presence of the ruthenium ions affects the electrochemical and optical properties of the films. Our results suggest that mixed films are formed by tungsten trioxide grains surrounded by ruthenium oxide phase. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

Synthesis of nanocrystalline SnO<Subscript>2</Subscript> in supercritical water

Nanocrystalline SnO₂ was synthesized in supercritical water at 385–415°C and 30 MPa (38–106 s residence time) in a tubular flow reactor from an aqueous solution of 0.1–0.4 M SnCl₄. The conversion rate was between 53 and 81%, but increased to 97.8% when 0.1 M NaOH was added. Nanoparticles were analyzed by a series of independent analytical techniques, including TEM, Raman, XRD, SEM, EDX and FT-IR. The initial size of the particles was about 3.7 nm. After calcination at 450°C for 2 h, the particle size increased to 4 nm. The particles were of low crystallinity, as indicated by the weak Raman and XRD signals. All particles were composed of Sn and O, as verified by the EDX spectra. The crystals were tetragonal, as confirmed by the weak XRD spectrum. After calcination at 600°C for 10 h, the particle size increased to 9 nm, while high crystallinity was confirmed by Raman and XRD analyses. All the crystals had the same structure, as indicated by TEM electron diffraction patterns. Using this one-step supercritical water process, nanoparticles of SnO₂ can be conveniently produced continuously in a flow reactor in less than 2 min.