ZnO nanocrystalline powders were fabricated by the solutions prepared by dissolving zinc acetate in isopropyl alcohol. Ethanolamine was used to enhance the solubility of acetates. Nanocrystalline powders were obtained either from the dried gels or precipitated solutions followed by calcination at different temperatures. Microstructural characterization of the powders showed that both morphology and the crystallite size of powders significantly altered based on the fabrication method and the calcination temperature.
Nanocrystalline powders of GaN with grain sizes ranging from 2 to 30 nm were examined under high external pressures by in situ diffraction techniques in a diamond anvil cell at DESY (HASYLAB, Station F3). The experiments on densification of pure powders under high pressure were performed without a pressure medium. The mechanism of generation and relaxation of internal strains and their distribution in nanoparticles was deduced from the Bragg reflections recorded in situ under high pressures at room temperature. The microstrain was calculated from the full-width at half-maximum (FWHM) values of the Bragg lines. It was found that microstrains in GaN crystallites are generated and subsequently relaxed by two mechanisms: generation of stacking faults and change of the size and shape of the grains occurring under external stress.
This study presents the results of the synthesis of silver chloride nanoparticles dispersed within ammonium nitrate matrix via displacement mechanochemical reaction NH_{4}Cl + AgNO_{3} + zNH_{4}NO_{3} = (z+1)NH_{4}NO_{3} + AgCl at z = z_{1}= 7.22 and z = z_{2}= 3.64. The intermediate compound, NH_{4}Ag(NO_{3})_{2}, was identified after mechanochemical processing of studied system. Use of simultaneous thermogravimetry and differential scanning calorimetry provide a new means for preparing silver chloride nanoparticles in their free form by thermal treatment.
Ce doped La_{1-x}Sr_xCo_{1-y}Fe_yO_3 (LCSCF) is a widely used cathode material due to its high catalytic activity for oxygen reduction and high oxygen exchange coefficient. LCSCF is also known with its high ionic and electronic conductivities and low electrode polarization losses which are highly critical properties for low temperature solid oxide fuel cell applications. In this study, structural properties of the LCSCF cathode nanopowder materials synthesized by glycine-nitrate gel combustion have been investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and nanosizer. Synthesized nanopowders represent volcanic ash like structures and morphologies. Ce, Sr, Co, and Fe are found to have significant effects on the structural properties of powders in terms of powders morphology, agglomerate structure, crystallite size and also lattice parameter of perovskite crystal. All synthesized ash powders have particle sizes around 50-600 nm, varying crystalline structures of perovskite and fluorite depending on molar ratio of Ce in the composition. Increasing molar Ce ratio over 0.4 is found to lead to the formation of a separate nano ceria phase in fluorite crystal structure on the surface of the synthesized powder.
The morphology and other physical properties of ZnO nanopowders synthesized by glycine-nitrate gel combustion process were investigated and characterized by scanning electron microscopy, transmission electron microscopy, nanosizer and X-ray diffraction. Glycine, NH_2CH_2COOH, and zinc nitrate Zn(NO_3)_2·6H_2O were dissolved in distilled water and the solution was coagulated by mixing at 90°C. The viscous gel prepared during glycine-nitrate mixing was heated at ≈220C to initiate the exothermic reactions by self-combustion where the temperature reached up to 1200°C. The glycine-nitrate ratio had a significant effect on the reaction temperature and final particle morphology. Therefore the synthesized powders have a different morphology like formless and spherical tufa ash. The particle size distribution was 50-1200 nm as measured using a nanosizer.
The aim of the research presented is to investigate the effect of pH value on the structural and morphological properties of nanostructured ZnO products. Zinc acetate dihydrate (Zn(CH_3COO)_2·2H_2O) has been used as precursor whereas distilled water is used as a solvent. The pH value of the sol was adjusted with monoethanolamine (MEA) and it changed from acid to base in nature. X-ray diffractometer has been used to determine preferred crystal orientation and particle size of the thin films. Film morphologies have been examined by using JEOL JSM 6060 LV scanning electron microscope equipped with energy-dispersive spectroscopy.
In this work we evaluate structural and optical properties of ZnO nanoparticles grown by wet chemistry method. Light emission properties of these nanoparticles are studied with cathodoluminescence and micro-photoluminescence. Even at the room temperature excitonic emission is well resolved, due to high exciton binding energy of ZnO. Decay kinetics of photoluminescence emissions and efficiency of inter-nanoparticles energy migration is evaluated from maps of in-plane variations of photoluminescence decay times measured in microphotoluminescence setup.
X-ray diffraction, micro-Raman and the Fourier transform infrared spectroscopies as well as magnetometry measurements were performed on nanosized manganese oxides to probe their phase composition and magnetic properties. It was shown that the XRD method is less sensitive to phase composition of manganese oxide samples than spectroscopic methods. While in some samples the XRD method recognised only the manganosite MnO phase, the Raman and FT-IR methods revealed additionally the presence of the hausmannite Mn₃O₄ phase.
TiO_{2} particles were deposited onto the surface of polyester (PES) material. The microbiological research were carried out on two bacteria strains: Staphylococcus aureus and Klebsiella pneumoniae, which showed antibacterial properties of the PES surfaces modified with the titanium dioxide under the influence of UV radiation.
Pure and La-doped titania (TiO_2) nanopowders are synthesized by sol-gel technology. The crystallite sizes determined by X-ray diffraction measurements range from 10 to 15 nm. Dependence of structural and morphological characteristics of nanopowders on synthesis conditions and La^{3+} content is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of TiO_2. Additional Raman modes of extremely low intensity can be related to the presence of a small amount of brookite amorphous phase in nanopowders, which is in accordance with the results of X-ray diffraction analysis. The particle size distribution in TiO_2 nanopowders was estimated from the low frequency Raman spectra, using the fact that the phonon modes in nanosized TiO_2 observed in the low frequency region (ω <40 cm^{-1}) can be well described by the elastic continuum model, assuming that nanoparticles are of perfect spherical shape and isotropic. The nanosized particle distribution obtained by this method is used for the calculation of the frequency and shape of the most intensive E_g Raman mode in anatase TiO_2 by the phonon confinement model. The calculated broadening of this mode, associated with the particle size distribution, coincides well with the characteristics of E_g mode observed in measured Raman spectra of TiO_2 nanopowders. This confirms the Raman spectroscopy method as a powerful tool for determination of particle size distribution in nanosized materials.
Nanocrystalline Ni-ferrite was synthesized by modified precipitation method in which soluble starch is used as dispersing agent and Na_{2}CO_{3} as a precipitating agent. NiSO_{4}·6H_{2}O and Fe(NO_{3})_{3}·9H_{2}O were used as precursors for nickel and ferric oxide, respectively. The obtained nanocrystalline Ni-ferrite was analysed and discussed through structural, compositional and magnetic characterization. Formation of pure NiFe_{2}O_{4} phase with average crystallite size of 21 nm has been confirmed by X-ray diffraction analysis (XRD). The determined phase composition was additionally supported by results of ^{57}Fe Mössbauer phase (MS) analysis and material's nanocrystalline structure by field emission scanning electron microscopy (FE-SEM). Thermomagnetic behaviour was studied up to 800 °C. The obtained room temperature magnetic hysteresis loop, recorded by means of a vibrating sample magnetometer (VSM), exhibits characteristic "S" shape of the soft magnetic material with the measured coercivity of about 10 kA/m and the specific moment up to 40 Am^{2}/kg.
The mechanochemical synthesis of nanocrystalline CuFeSe₂ particles prepared by high-energy milling in a planetary mill in an argon atmosphere from copper, iron, and selenium for 60 min is reported for the first time. The CuFeSe₂ nanoparticles crystallize in tetragonal structure with mean crystallite size of about 32±1 nm. High resolution transmission electron microscopy measurements confirmed the presence of agglomerates which are formed by small nanocrystalline domains (5-40 nm). The magnetic data revealed that paramagnetic CuFeSe₂ nanoparticles coexist with a small amount of ferromagnetic impurities at room temperature. The magnetic transition towards a weak ferromagnetic or ferrimagnetic behavior occurs in CuFeSe₂ at approximately 79 K. The band gap of the CuFeSe₂ particles is 0.95 eV which is wider than the band gap in bulk materials (0.16 eV), which could be in many aspects of application more beneficial.
Nickel ferrite (NiFe_2O_4) and manganese ferrite (MnFe_2O_4) have been prepared by a soft mechanochemical route from mixture of (1) Ni(OH)_2 and α-Fe_2O_3 and (2) Mn(OH)_2 and α-Fe_2O_3 powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the NiFe_2O_4 and MnFe_2O_4 spinel phases were followed by X-ray diffraction, Raman and infrared spectroscopy, scanning and transmission microscopy. The spinel phase formation was first observed after 4 h of milling (case 1) and after 3 h (case 2) and its formation was completed after 25 h in both cases. The synthesized NiFe_2O_4 and MnFe_2O_4 ferrites have a nanocrystalline structure with a crystallite size of about 30 and 40 nm for cases (1) and (2), respectively. There are five Raman and four IR active modes. In order to understand better the whole process of phase formation, the Mössbauer measurements were done.
Multiferroic bismuth ferrite (BiFeO_{3}) nanopowders have been obtained at room temperature by mechanochemical synthesis. Depending on the post-synthesis processing the nanopowders exhibited differences in the mean sizes, presence of amorphous layer and/or secondary phases. Extended magnetic study performed for fresh, annealed and hot-pressed nanopowders revealed substantial improvement of the magnetic properties in the as-prepared powder.
Tin dioxide nanoparticles were synthesized by sol-gel method and calcined at different temperatures in the range 350-750°C. The SnO_2 precursor solution was prepared from SnCl_2 ·2H_2O (tin (II) chloride dihydrate), and chloride ions were removed from the solution before the sol-gel synthesis was applied. SnO_2 powders were characterized by thermal analyses, X-ray diffraction, field emission gun-scanning electron microscopy, and energy dispersive X-ray spectroscopy, and grain size of nanoparticles were determined by using the Debye-Scherrer formula.
The mechanical alloying process has been used to prepare nanocrystalline Cu_{70}Fe_{18}Co_{12} alloy from elemental Cu, Fe and Co powders in a planetary ball mill under argon atmosphere. The interdiffusion of Cu, Fe and Co leads to a heterogeneous solid solution with Cu-Fe-Co rich environments after 12 h of milling. The end product is a mixture of a highly disordered structure, fcc-Cu (Fe-Co), phase having different microstructural and structural parameters. For all the elaborate series, the evolution of coercive field and the remanence according to the time of milling is analyzed. The coercivity, H_{c}, decreases rapidly up to 8 h of milling to about 0.3 A/m and then the coercivity, increases to a maximum at 54 h. The influence of the time of milling at the resistivity of these alloys is shown.
Positron lifetime spectroscopy is employed in a comparative study of several zirconia-based materials: (i) the pressure-compacted nanopowders of the three zirconia polymorphs - pure ZrO_2 (monoclinic), yttria-stabilized ZrO_2+3 mol.% Y_2O_3 (tetragonal) and yttria-stabilized ZrO_2+8 mol.% Y_2O_3 (cubic), (ii) ceramic materials obtained by sintering of the above two yttria-stabilized zirconia nanopowders and (iii) the tetragonal and cubic yttria-stabilized zirconia monocrystals. Positron lifetime data observed on the nanopowders suggest that the two shortest components, exhibiting lifetimes of ≈180 and ≈370 ps, arise from the annihilation of positrons trapped in defects associated with grain boundaries, presumably the vacancy-like defects and tripple points, respectively. Positron lifetime spectra observed on the ceramic materials resemble those found for the corresponding monocrystals, giving thus an additional support to the above interpretation of the nanopowders results.
This study reports on the development of some W-Cu-Ni materials for use as electrical contacts for low voltage vacuum switching contactors for nominal currents up to 630 A. The contact materials with 85 wt% W, 12-14 wt% Cu and 1-3 wt% Ni were obtained by spark plasma sintering process in vacuum. From very finely dispersed W-Cu-Ni powder mixtures there were produced sintered electrical contact pieces that were investigated in terms of physical, microstructural, mechanical, and functional properties. The material sintered at 1200C exhibited a near fully dense structure with very low porosity and enhanced mechanical properties: hardness of maximum 480 HV1 and elastic modulus of maximum 220 GPa and low chopping current of maximum 1.77 A.
Four series of ZnO nanopowders obtained by a microwave hydrothermal method are examined. Two different solvents (ethanol and distilled water) and different values of pressure during heating in the reactor were used. The obtained nanopowders show a bright emission covering visible light spectral region, including the band edge emission. Results of scanning electron microscopy, X-ray diffraction, photo- and cathodoluminescence investigations and also CIE1961 chromaticity diagram are presented.
Two series of ZnO nanopowders obtained by a microwave hydrothermal method are examined. We used two different zinc precursors (zinc chloride (ZnCl_2) and zinc nitrate hexahydrate (N_2O_6Zn·6H_2O)). Both types of nanopowders show a bright emission in a visible light, including the band edge emission, which indicates their good crystallographic quality. Results of scanning electron microscopy, photo- and cathodoluminescence investigations are presented.
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