Effect of spin polarization on the optical properties of Co-doped TiO2 thin films

A non-linear variation of bandgap energy with Co doping is observed in sputter deposited Co-doped TiO₂ thin films. This peculiar behavior is explained on the basis of mechanical stress in the films together with spin polarization due to s,p-d exchange interaction between the localized Co 3d electrons and delocalized electrons. Quantitative analyses of mechanical stress and grain boundary barrier potential due to spin polarization are performed from the below bandgap absorption tail. Furthermore, anomalous variations in both the refractive indices and extinction coefficients with Co doping are noted and are explained on the basis of ab-initio calculations based on density functional theory.     

Characterization of ultrafine zirconia and iron oxide powders prepared under hydrothermal conditions

Abstract

Nanocrystalline zirconia (6-20 nm) and iron oxide (20-80 nm) powders were produced by hydrothermal treatment of corresponding hydroxides and nitrate solutions. The synthesis parameters (temperature, duration, concentration) allow fabrication of ultrafine oxide powders with various particle size and morphology. The smallest particles were produced by short-time (4-7 s) treatment of nitrate solutions (PH ≈ 1). Prepared nanocrystalline powders exhibit high activity in model solid state reactions.     

Development of electroless Ni-Zn-P/nano-TiO2 composite coatings and their properties

Ni-Zn-P-TiO₂ composite coatings were successfully obtained on low carbon steel by electroless plating technique. Deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis (EDS) studies. The hardness and microstructure of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ composite coatings were analyzed. The change in microstructure and higher hardness was noticed for heat treated composite. The corrosion resistance behavior of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5 wt% NaCl solution. The composite coating exhibited enhanced corrosion resistance property over Ni-Zn-P coating.     

Effect of phase transformation on optical and dielectric properties of zirconium oxide nanoparticles

Zirconium oxide nanoparticle (ZrO₂) is synthesized by the hydrothermal method at different calcination temperatures. The structural analysis is carried out by X-ray diffraction and Raman spectra. The sample prepared at 400 °C and 1100 °C showed the cubic and monoclinic phase, respectively, and the sample calcined at 600 °C and 800 °C showed the mixed phase with co-existence of cubic and monoclinic phases. Furthermore, the morphology and particle size of these samples were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. The band gap estimated from UV–Vis spectra of ZrO₂ (zirconia) nanocrystalline materials calcined at different temperatures from 400 °C to 1100 °C was in the range of 2.6–4.2 eV. The frequency dependence of dielectric constant and dielectric loss was investigated at room temperature. The low frequency region of dielectric constant is attributed to space charge effects.     

Polyacrylonitrile electrolytes: 1. A novel high-conductivity composite polymer electrolyte based on PAN, LiClO4 and α-Al2O3

In this work, a series of novel solid-type α-Al₂O₃-containing polyacrylonitrile (PAN)-based composite polymer electrolytes (CPE) with high conductivity and high mechanical property at room temperature has been prepared. The effect of the addition of α-Al₂O₃ on the properties of the PAN-based composite polymer electrolyte has been analyzed. The best conductivities obtained at room temperature is 5.7×10⁻⁴ S cm⁻¹ from the CPE with 7.5 wt.% α-Al₂O₃ and 0.6 LiClO₄ per PAN repeat unit. The stress–strain test result indicates that the membranes prepared possess high yield stress (73 kg cm⁻²) suitable for serving as separators in the solid-state lithium and lithium ion batteries and high yield elongation (225%) pliable to form good interface with electrodes. Also discussed are the effects of the addition of the ceramics on the interactions in the system and the possible conduction mechanism.     

Studies on the structure and transport properties of hexanoyl chitosan-based polymer electrolytes

Polymer electrolytes composed of hexanoyl chitosan as the host polymer, lithium trifluoromethanesulfonate (LiCF₃SO₃) as the salt, diethyl carbonate (DEC)/ethylene carbonate (EC) as the plasticizers were prepared and characterized by X-ray diffraction and impedance spectroscopy. The X-ray diffraction results reveal the variation in conductivity from structural aspect. This is reflected in terms of amorphous content. Sample with higher amorphous content exhibits higher conductivity. In order to further understand the source of the conductivity variation with varying plasticizers compositions as well as temperatures, the ionic charge carrier concentration and their mobility in polymer electrolyte were determined. The Rice and Roth model was proposed to be used to estimate the ionic charge carrier concentration, n. Knowing n and combining the result with dc conductivity, the mobility of the ionic charge carrier can be calculated. It is found that the conductivity change with DEC/EC composition is due mainly to the change in ionic charge carrier concentration while the conductivity change with temperature is due primarily to the change in mobility.     

XPS investigation of diffusion of two-layer ZrO2/SiO2 and SiO2/ZrO2 sol–gel films

Two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were deposited on K9 glass substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy (XPS) technique was used to investigate the diffusion of ZrO₂/SiO₂ and SiO₂/ZrO₂ films. To explain the difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films, porous ratio and surface morphology of monolayer SiO₂ and ZrO₂ films were analyzed by using ellipsometry and atomic force microscopy (AFM). We found that for the ZrO₂/SiO₂ films there was a diffusion layer with a certain thickness and the atomic concentrations of Si and Zr changed rapidly; for the SiO₂/ZrO₂ films, the atomic concentrations of Si and Zr changed relatively slowly, and the ZrO₂ layer had diffused through the entire SiO₂ layer. The difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films was influenced by the microstructure of SiO₂ and ZrO₂.     

Intrinsic defect related luminescence in ZrO2

The studies of ZrO₂ and yttrium stabilized ZrO₂ nanocrystals luminescence as well as yttrium stabilized single crystal luminescence and induced absorption showed that the intrinsic defects are responsible for luminescence at room temperature. These defects form a quasi-continuum of states in ZrO₂ band gap and are the origin of the luminescence spectrum dependence on the excitation energy. Luminescence centers are oxygen vacancies related but not the vacancies themselves. At room temperature, in ZrO₂, deep traps for electrons and holes exist. The oxygen vacancies are proposed to be the traps for electrons.     

Microstructure and mechanical properties of Al2O3-Al composite coatings deposited by plasma spraying

Al₂O₃ and Al₂O₃-Al composite coatings were prepared by plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction (XRD), while optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphology of impacted droplets, polished and fractured surface, and the element distribution in terms of wavelength-dispersive spectrometer (WDS). Mechanical properties including microhardness, adhesion and bending strength, fracture toughness and sliding wear rate were evaluated. The results indicated that the addition of Al into Al₂O₃ was beneficial to decrease the splashing of impinging droplets and to increase the deposition efficiency. The Al₂O₃-Al composite coating exhibited homogeneously dispersed pores and the co-sprayed Al particles were considered to be distributed in the splat boundary. Compared with Al₂O₃ coating, the composite coating showed slightly lower hardness, whereas the coexistence of metal Al phase and Al₂O₃ ceramic phase effectively improved the toughness, strength and wear resistance of coatings.     

Ni-MH battery based on plasticized alkaline solid polymer electrolytes

Solid-state nickel metal hydride cells were fabricated using plasticized alkaline solid polymer electrolytes (ASPE) prepared from polyvinyl alcohol (PVA), potassium hydroxide (KOH), alumina (α-Al₂O₃), and propylene carbonate (PC). The ASPE film with PVA/KOH/α-Al₂O₃/PC/H₂O weight ratio of 1.00:0.67:0.09:2.64:1.32 and conductivity of (6.6 ± 1.7) × 10⁻⁴ S cm⁻¹ was used in fabrication of the electrochemical cells. To investigate the electrochemical properties of the plasticized ASPE, cells with the configuration Mg₂Ni/plasticized ASPE/Ni(OH)₂ were fabricated. At the eighth cycle with a current drain of 0.1 mA and plateau voltage of ∼1.1 V, the discharge lasted for 14 h before the cell was considered to have failed. The failure mode of the cell was due to the formation of thin Mg(OH)₂ insulating layers.     

Study of electrical conductivity changes and phase transitions in Co3O4 doped ZrO2

The electrical conductivity of ZrO₂ doped with Co₃O₄ has been measured at various temperatures for different molar ratios. The conductivity increases due to the migration of vacancies created by doping. The conductivity is also found to increase with rise in temperature up to 120°C, and after attaining a maximum the conductivity decreases due to a collapse of the lattice framework. A second rise in conductivity around 460°C in all the compositions confirms the phase transition in ZrO₂ from monoclinic to tetragonal symmetry. X-ray powder diffraction and DTA studies were carried out for confirming the doping effects and the transition in ZrO₂.     

Characterization and compositional study of a ZrO2 engineering ceramic irradiated with a fibre laser beam

Fibre laser surface treatment (FLST) of a cold isostatic pressed (CIP) ZrO₂ engineering ceramic (ZEC) was performed using various processing gas compositions. This is the first time that a surface treatment of ZEC has been employed hitherto by using the fibre laser (FL) radiation to observe the changes on and within the surface of the engineering ceramic; in particular, material removal, surface topography, chemical composition, changes in the surface hardness and distribution of the heat affected zone (HAZ). Bonding of the grain boundaries was found through surface melting with all FL irradiated samples to some extent, but the effect was more marked on the sample FL irradiated with an Ar assist gas and proved to be the most effective combination for modifying the surface morphology. The surface finish and the material removal were varied with the changes in the gas composition. Maximum material removal was observed when an O₂ assist gas was employed on account of the O₂ generating an exothermic reaction. This in turn, produced excessive heating. The compositional analysis revealed a chemical change occurring within the FL irradiated surfaces, regardless of the assist gas used, with the ZEC transforming to zirconia carbide (ZrC).     

外电场下二氧化锆的分子结构及其特性

对O原子采用6-311++G*基组,Zr原子采用aug-cc-pVTZ-PP基组,利用密度泛函(B3P86)方法优化得到了ZrO2分子的稳定构型,并研究了不同外电场(0—0.025 a.u.)作用下ZrO2基态分子键长、能量、电荷分布、偶极矩和能级的变化规律.在优化构型的基础上,利用含时密度泛函(TD-B3P86)方法研究了ZrO2分子在外电场作用下前6个激发态的激发能、跃迁波长和振子强度的激发特性.研究结果表明:随着电场强度的增大,Zr—2O的键长增大,而Zr—3O的键长均匀减少,总能量降低,偶极矩增大;最高占据轨道能量基本保持不变,最低未占据轨道和能隙均减小.电场的增大使得激发能减小,各个激发态跃迁波长均发生不同程度的红移现象,因而,利用外电场可以控制ZrO2的发光光谱范围在可见-红外区域扩展.     

Correlation between interfacial interactions and mechanical properties of PA-6 doped with surface-capped nano-silica

The polyamide-6 pellets were mixed with nano-SiO₂ particles surface-capped by 3-aminopropyltriethoxysilane (APS) via a melt blending route. PA-6 composites doped with surface-capped nano-SiO₂ (designated as PAMNS, where AMNS refers to APS surface-capped nano-SiO₂). AMNS and the silica samples (designated as EAMNS) extracted by acid etching from various PAMNS samples containing different concentration of amino functional groups on surface-capped nano-silica surfaces were characterized by means of Fourier transformation infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). This aims at revealing the interfacial interaction between AMNS and PA-6 matrix and its effect on the mechanical properties of the filled PA-6 composites. The chemical features and microstructures of the PAMNS composites were analyzed by means of FTIR and transmission electron microscopy (TEM), respectively, while their mechanical properties were evaluated using standardized test rigs. Results demonstrate that the surface-modified nano-SiO₂ particles were uniformly dispersed in PA-6 matrix. The residue silica extracted from various PAMNS samples showed characteristic FTIR absorbance peak of PA-6 and had larger weight losses than AMNS, implying that the polymeric matrix was chemically bonded with the nanofiller particles. The interfacial interactions are closely related to the concentration of functional groups in AMNS, and there might exist a critical concentration at which the strongest interfacial interactions could be reached. Beyond the critical concentration of the functional groups in AMNS, the mechanical properties of the filled PA-6 composites tended to decrease to some extent.     

MOCVD of zirconium oxide thin films: Synthesis and characterization

The synthesis of thin films of zirconia often produces tetragonal or cubic phases, which are stable at high temperatures, but that can be transformed into the monoclinic form by cooling. In the present study, we report the deposition of thin zirconium dioxide films by metalorganic chemical vapor deposition using zirconium (IV)-acetylacetonate as precursor. Colorless, porous, homogeneous and well adherent ZrO₂ thin films in the cubic phase were obtained within the temperature range going from 873 to 973 K. The deposits presented a preferential orientation towards the (1 1 1) and (2 2 0) planes as the substrate temperature was increased, and a crystal size ranging between 20 and 25 nm. The kinetics is believed to result from film growth involving the deposition and aggregation of nanosized primary particles produced during the CVD process. A mismatch between the experimental results obtained here and the thermodynamic prediction was found, which can be associated with the intrinsic nature of the nanostructured materials, which present a high density of interfaces.     

The interface structure of nano-SiO2/PA66 composites and its influence on material's mechanical and thermal properties

The PA66-based nanocomposites containing surface-modified nano-SiO₂ were prepared by melt compounding. The interface structure formed in composite system was investigated by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The influence of interface structure on material's mechanical and thermal properties was also studied. The results indicated that the PA66 chains were attached to the surface of modified-silica nanoparticles by chemical bonding and physical absorption mode, accompanying the formation of the composites network structure. With the addition of modified silica, the strength and stiffness of composites were all reinforced: the observed increase depended on the formation of the interface structure based on hydrogen bonding and covalent bonding. Furthermore, the differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that the presence of modified silica could affect the crystallization behavior of the PA66 matrix and lead to glass transition temperature of composites a shift to higher temperature.     

First-principles studies of structural,mechanical, electronic,optical properties and pressure-induced phase transition of CuInO2 polymorph

Using the first-principles density-functional theory within the generalized gradient approximation (GGA), we have investigated the structural, elastic, mechanical, electronic, and optical properties and phase transition of CuInO₂. Structural parameters including lattice constants and internal parameter, pressure effects and phase transition pressure were calculated. We have obtained the elastic coefficients, bulk modulus, shear modulus, Young's modulus and Poisson's ratio. We find that two phases of CuInO₂ are indirect band gap semiconductors (F–Γ and H–Γ for 3R and 2H, respectively). Optical properties, including the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function and optical conductivity have been obtained for radiations of up to 30 eV.     

Improved Ionic Conductivity of NBR/Epoxy Resin/LiClO4 Composites by Adding Ionic Liquid

Solid polymer electrolyte with high ionic conductivity was prepared by adding an ionic liquid, 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIMOTF) to the nitrile butadiene rubber/epoxy resin/LiClO₄ (NBR-EP-Li) system. The addition of BMIMOTF into NBR-EP-Li composites, with the LiClO₄/BMIMOTF mole ratio of 1/0.54, improved the conductivity by 6–17 times depending on the amount of LiClO₄. Infrared difference spectroscopy and nuclear magnetic resonance spectroscopy analysis confirmed the interaction between LiClO₄ and BMIMOTF, which caused a decreasing interaction between ClO₄ ^? and Li⁺. X-ray diffraction and field emission scanning electron microscopy analysis indicated BMIMOTF improved the dissolution of LiClO₄ and contributed to the increase of conductivity by an increase of free Li⁺.     

Ionic conduction in plasticized PVC/PAN blend polymer electrolytes

Blended polymer electrolytes with poly(vinyl chloride) (PVC)–poly(acrylonitrile) (PAN) were prepared with different plasticizer concentrations and constant lithium perchlorate (LiClO₄) ratio by the solution-casting technique. The structure and complexation of the prepared films were studied by X-ray diffraction and Fourier transform infrared spectroscopy. The effect of the plasticizer on the ionic conduction in these electrolytes was investigated using alternating current impedance measurement and discussed. The temperature-dependant ionic conductivity was carried out in the range 302–373 K. The prepared films were also examined by thermogravimetry/differential thermal analysis to determine their thermal stability.     

PEO electrolytes containing dioctyl phthalate (DOP) for dye-sensitized nanocrystalline TiO2 solar cells

In this paper, we aim to prepare polymer electrolytes consisting of NaI and I₂ dissolved in poly(ethylene oxide) (PEO) and dioctyl phthalate (DOP) as an additive and apply the electrolytes to dye-sensitized solar cells (DSSC). Upon the incorporation of salt, the phthalic-stretching C=O bands of DOP in Fourier transform infrared spectra shifted to a lower wave number (Δf = 93 cm⁻¹), confirming the unusual strong complex formation between sodium ions and phthalic oxygen. Coordinative interactions and structural changes of PEO/NaI/I₂/DOP electrolytes have also been characterized by wide angle X-ray scattering, presenting an almost amorphous structure of the polymer electrolytes. The ionic conductivity of the polymer electrolytes reached ∼10^–4 S/cm at room temperature at the mole ratio of [EO]:[Na]:[DOP] = 10:1:0.5, as determined by the four-probe method. DSSC using the polymer electrolytes and conductive indium tin oxide glasses exhibited 2.9% of overall energy conversion efficiency (=P _max/P _in × 100) at one sun condition (100 mW/cm²). The good interfacial contact between the electrolytes and the dye-attached nanocrystalline TiO₂ layers were verified by field-emission scanning electron microscopy.