Influence of imidazolium-based ionic liquids on the performance of polyaniline-CoFe2O4 nanocomposites

Using cobalt ferrite (CoFe₂O₄) nanoparticles of different content as nucleation sites, polyaniline-CoFe₂O₄ nanofiber composites were successfully synthesized at the interface of water and ionic liquid via in-situ polymerization. Structure and morphology were investigated by TGA, TEM, XRD, and FT-IR. The influence of ionic liquids on the structure, conductivity and magnetic property of polyaniline-CoFe₂O₄ nanocomposites were studied in detail. The results show that imidazolium-based ionic liquids BMIPF₆ acts as an anchor agent during the nanofiber composites formation process. Introduction of ionic liquids obviously improves the conductivity but weakens the magnetization of polyaniline-CoFe₂O₄ nanocomposites in the same [CoFe₂O₄]/[An] ratio.     

Hierarchical CuO hollow microspheres: Controlled synthesis for enhanced lithium storage performance

In this work, hierarchical CuO hollow microspheres were hydrothermally prepared without use of any surfactants or templates. By controlling the formation reaction conditions and monitoring the relevant reaction processes using time-dependent experiments, it is demonstrated that hierarchical CuO microspheres with hollow interiors were formed through self-wrapping of a single layer of radically oriented CuO nanorods, and that hierarchical spheres could be tuned to show different morphologies and microstructures. As a consequence, the formation mechanism was proposed to proceed via a combined process of self-assembly and Ostwald's ripening. Further, these hollow microspheres were initiated as the anode material in lithium ion batteries, which showed excellent cycle performance and enhanced lithium storage capacity, most likely because of the synergetic effect of small diffusion lengths in building blocks of nanorods and proper void space that buffers the volume expansion. The strategy reported in this work is reproducible, which may help to significantly improve the electrochemical performance of transition metal oxide-based anode materials via designing the hollow structures necessary for developing lithium ion batteries and the relevant technologies.     

Synthesis and characterization of spray deposited PdO-NiO-SDC composite anode material for potential application in IT-SOFC

The synthesis of mixed conducting PdO-NiO-SDC composite films has been reported for the first time by a simple and cost effective spray pyrolysis technique. The films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. The structure, morphology and electrical properties of the films were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM) and impedance spectroscopy (IS). The substrate and annealing temperatures were optimized for obtaining nano-crystalline, porous, adherent and composite films with PdO, NiO and SDC phases. Films showed good microstructure with sufficient porosity and good connectivity of the deposited material. Crystallite size of the deposited material was found to be in the range of 7-9 nm. The deposited film showed high oxygen ion conductivity, 3.94 × 10⁻¹ S cm⁻¹ at 350 °C. Due to their nano-crystalline, porous and composite nature the spray deposited PdO-NiO-SDC films may have high three phase boundary area and hence can be considered as an anode for intermediate temperature solid oxide fuel cells.     

Characteristics of ZnO-B2O3-SiO2-CaO glass frits prepared by spray pyrolysis as inorganic binder for Cu electrode

ZnO-B₂O₃-SiO₂-CaO glass frits were directly prepared by high temperature spray pyrolysis for use in Cu electrodes. The frits prepared at temperatures above 1400 °C were spherical, amorphous, of fine size and dense structure. The mean particle size and geometric standard deviation of the frits prepared at 1400 °C were 0.87 μm and 1.37, respectively. The temperatures of glass transition, crystallization and melting were 454, 534 and 800 °C, respectively. The glass layer fired at 800 °C had a dense structure due to the material's complete melting, despite some crystals being observed by SEM. A copper electrode formed from copper paste with glass frits had a dense structure when fired at 800 °C. The specific resistances of electrodes formed from copper paste with and without glass frits were 2.5 and 8.5 μΩ cm, respectively.     

Luminescent properties of ytterbium-doped ternary lanthanum chloride

Studies of the absorption and temperature dependence of photoluminescence spectra and luminescence decay times of the intra-shell f-f transitions (²F_5/2 ↔ ²F_7/2) of Yb³⁺ ions in K₂LaCl₅:Yb³⁺ powders with 5, 10, 15 and 25% of ytterbium are presented. The spectroscopic properties of the powders with different ytterbium content are compared. Experiments were performed at the temperatures from 25 to 300 K. The strong emission around 982 nm has been observed under direct excitation of the luminescence center with 960 nm line of continuous wave Ti:sapphire laser pumped by Ar-ion laser. The temperature quenching effect of the luminescence was rather week, especially in the samples with higher concentration of ytterbium (15 and 25%). Additionally the probability of the f-f radiative transitions of the Yb³⁺ ions in these powders was almost temperature independent for more heavily doped samples (with 15 and 25% of Yb) and only weakly temperature dependent for less doped samples (with 5 and 10% of Yb). These results reveal high thermal stability of the optical properties of the examined powders.     

Influence of the oxygen content and the preparation method on the power factor of PrBaCo2O5+δ samples (0.54 ≤ δ ≤ 0.84)

In this work, we focus on the influence of the oxygen content and the preparation method on the power factor of different PrBaCo₂O_5+δ samples (0.54 ≤ δ ≤ 0.84). The samples have been initially synthesized by the Pechini method. Their oxygen content has been subsequently modified by annealing under argon/oxygen flow or by electrochemical oxidation/reduction. The oxygen stoichiometry has a high impact on the electrical conductivity and Seebeck coefficient of the resulting materials. Moreover, by adequately reducing their oxygen content while increasing their intergrain conductivity (by increasing the particle size and degree of sintering) the power factor of these samples can be drastically improved. The best result is shown by the PrBaCo₂O_5.54 sample, that was annealed at high temperature under argon flow, whose power factor is as high as 6.5 μW/K² cm⁻¹ at ∼135 K, more than two orders of magnitude higher than that shown by the initial PrBaCo₂O_5.76 reference sample.     

Bandgap engineering by substitution of S by Se in nanostructured ZnS1−xSex thin films grown by soft chemical route for nontoxic optoelectronic device applications

Thin films of nanostructured ZnS_1−xSe_x with optimized growth parameters were prepared by soft chemical route on glass substrates. Ammonia free precursors were used at 80 °C constant bath temperature. The ratio of sulphur to selenium was changed continuously by changing the composition x (0-1), while atomic concentration of zinc was kept constant. Structure, composition and surface morphology of as-deposited films were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX) and scanning electron microscopy (SEM), atomic force microscopy (AFM) respectively. XRD studies revealed that as-deposited films were nanostructured in nature with cubic zinc blended structure. It was further observed that the preferred orientations are along (1 1 1) plane and crystallite size decreased with increase in the value of x. SEM and AFM images revealed that films were uniform and pinhole free. The optical band gap (E_g) was calculated from the observed transmittance spectra by Urbach method. It was found that the band gap varied linearly from 3.71 to 2.70 eV, as composition x varies 0-1. The electrical properties’ study revealed that the decrease in resistivity and increase in photosensitivity, as composition x varied 0-1. The observed interesting properties of ZnS_1−xSe_x thin films justified their significance in optoelectronic device fabrication and applications, and as an environment friendly alternative to the commonly used toxic material such as CdS.     

Photosensitive nanostructured TiO2 grown at room temperature by novel “bottom-up” approached CBD method

The current paper incorporates with a “bottom-up” approached chemical bath deposition method to grow titanium dioxide (TiO₂) nanostructure at room temperature on glass and stainless steel substrates. The room temperature deposited TiO₂ films are heat treated at 673 K for 1 h in air and the corresponding change in structural, morphological and optical properties are studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and UV-VIS-NIR spectrophotometer. The heat-treated films are utilized as a photocathode in photoelectrochemical (PEC) cell in 1 M NaOH electrolyte. The experimental results show that, the CBD method allows formation of photosensitive, anatase TiO₂ thin film, which can be potentially tuned in many functional applications with feasibility.     

Structure, ferroelectric/magnetoelectric properties and leakage current density of (Bi0.85Nd0.15)FeO3 thin films

In this paper, we report on the structure, ferroelectric/magnetoelectric properties and improvement of leakage current density of (Bi_0.85Nd_0.15)FeO₃ (BNFO) thin films deposited on Pt(1 1 1)/Ti/SiO₂/Si substrates from the polymeric precursor method. X-ray patterns and Rietveld refinement indicated that BNFO thin films with a tetragonal structure can be obtained at 500 °C for 2 h in static air. Field emission scanning electron, atomic force and piezoelectric force microscopies showed the microstructure, thickness and domains with polarization-oriented vectors of BNFO thin films. Ferroelectric and magnetoelectric properties are evident by hysteresis loops. The magnetoelectric coefficient measurement was performed to show the magnetoelectric coupling behavior. The maximum magnetoelectric coefficient in the longitudinal direction was close to 12 V/cm Oe. Piezoresponse force microscopy micrographs reveal a polarization reversal with 71° and 180° domain switchings and one striped-domain pattern oriented at 45° besides the presence of some nanodomains with rhombohedral phase involved in a matrix with tetragonal structure. The cluster models illustrated the unipolar strain behavior of BNFO thin films. The leakage current density at 5.0 V is equal to 1.5 × 10⁻¹⁰ A/cm² and the dominant mechanism in the low-leakage current for BNFO thin films was space-charge-limited conduction.     

Diphenylthiocarbazone (dithizone)-assisted solvothermal synthesis and optical properties of one-dimensional CdS nanostructures

One-dimensional (1D) cadmium sulfide (CdS) nanostructures with various aspect ratios were successfully synthesized by a diphenylthiocarbazone (dithizone)-assisted solvothermal method. The results showed that the dithizone-assisted synthesized samples had larger aspect ratio than that prepared in the absence of dithizone, and CdS nanowires with the highest aspect ratio were obtained with an appropriate dithizone amount (0.03 g/50 ml ethylenediamine in the present system). All the 1D CdS nanostructures were in hexagonal wurtzite phase. The as-synthesized large-scale CdS nanowires were in diameters ranging from 70 to 80 nm, length up to 20 μm, and aspect ratios of 250-285. Further characterization indicated that the CdS nanowires were single crystalline with a preferential growth orientation of [0 0 2], c-axis. Two optical absorption peaks were observed at about 488 nm and 502 nm for the CdS nanowire sample with high aspect ratio in the optical absorption spectroscopy, which could be attributed to the nanometer effect of nanowires. It was found that the additive dithizone was a crucial factor in controlling the morphology and optical properties of the 1D CdS nanostructures. The growth mechanism of 1D CdS nanostructure and the effects of dithizone in the present system were discussed.