جستجوی مقالات مرتبط با کلیدواژه « ژل » در نشریات گروه « زمین شناسی »

Al2O3/PVP nano-hybrid composite samples are synthesized using sol-gel method at 75°C. Weight percent of poly 4-vinyl phenol and aluminum oxide is 0.0, 0.28, 0.56, and 0.84. To study the nano-structural and electrical characteristics, X-ray diffraction, Fourier transfer infrared radiation, scanning electron microscopy, and atomic force microscopy are used. Dielectric constant of the samples is measured using “GPS 132 A” multi-meter. The results show that the highest amounts of dielectric constant at the frequency of 120 and 1 kHz are related to Al2O3 + 0.28 %wt. PVP(k=35) and Al2O3 + 0.56 %wt. PVP (k=26) nano-composite samples, respectively. Therefore, at the frequency of 120kHz, Al2O3 + 0.28 %wt. PVP nano-composite sample, due to having higher equivalent oxide thickness, less roughness, ohmicproperties, smaller size of nano-crystallites (Scherrer diameter of 45nm), higher dielectric constant, and as a result of less leakage current, is recommended as the gate dielectric for the future of organic field effect transistors.

SnO2 nanoparticles have been synthesized via sol-gel method in different annealing temperatures. TEM, FESEM and XRD techniques have been used to investigate the structure and morphology of SnO2 nanoparticles. The XRD pattern analysis shows all samples are single phase. XRD patterns show as the annealing temperature increases, the peaks become sharper which is related to the increase in the crystallite size of nanoparticles and enhancing the crystalline order and reducing lattice strain. The Williamson-Hall analysis and Halder-Wagner method were used to study the individual contributions of crystallite sizes and lattice strain to the peak broadening of nanoparticles. The physical parameters such as strain, stress and energy density values were calculated for three major reflection peaks of XRD patterns. Williamson-Hall analysis of XRD patterns show that increasing the annealing temperature causes the crystallite size to increase and to reduce lattice strain. TEM and FESEM images showed that by increasing temperature, nanoparticle size increases.

In this research, nanoparticles Bi1-x-yBayLaxFeO3 (BByLxFO (with values (x = 0.0, 0.05, 0.1) and (y = 0.0, 0.15) synthesized by a sol–gel  method. The structural, microstructural and magnetic properties have been investigated, using X-ray diffraction, Raman scattering, field emission scanning electron microscopy (FE-SEM), FTIR  spectroscopy, and magnetometry measurements at room temperature. The refinement of X-ray diffraction pattern of samples indicates a phase transition from rhombohedral (R3c) to rhombohedral-tetragonal. In addition, The refinement of X-ray Assigned  lattice parameters and unit cell volume.  Analysis of FT-IR confirmed Perovskite structure of samples. The FE-SEM analysis show nanoparticle size it decreases with La  concentration. Finally, the hysteresis loop of nanoparticle BByLyFO shows ferromagnetic behavior, that may be attributed to the collapse of spin structure and modifying exchange interactions because of La+3  and Ba+2 co-doping. The remenant  magnetization of  BB0.15L0.1FO sample (Mr = 1.166 emu/g) is approximately two and half times greater than that of  BB0.15L0FO (Mr = 0.514 emu/g). This enhancement in magnetic properties at room temperature can play an important role for the practical applications.

In this study, the effect of Ba substitution for Sr in the Bi-Pb-Sr-Ca-Cu-O (BPSCCO) system was investigated. The Bi1.6Pb0.4Sr2-xBaxCa2Cu3Oy superconductor with   0.0, 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 at annealing times of 16, 32, 48 and 64 hour was made by the sol-gel method. In order to study the microstructure of samples, SEM images and X-ray diffraction (XRD) was performed. The crystal lattice parameters of this compound were measured by using of diffraction angles and miller indices. The critical current density, critical temperature and at room temperature, resistivity of the samples were measured by four probe method. The results indicated that improved superconducting properties with Ba doping and the maximum values of the Bi-2223 phase fraction, critical temperature, current density and at room temperature resistivity are obtained for sample at annealing time of 32 hour with the Ba content
x = 0.2. Also, the results show that the critical current density decreases by increasing annealing time. The volume of the unit cell was increased by increasing the Ba doping, which indicates substitution of Sr by the Ba, with larger ionic radius.

In this research, Y3-xBixFe5O12 x = (0, 0.1, 0.2, 0.3) were synthesized by a sol–gel method. X-ray diffraction (XRD) patterns confirmed the pure spinel structure for all samples. The magnetic properties of the samples were investigated by the vibration sample magnetometer (VSM). The results obtained from VSM showed that saturation magnetization increases up to x = 0.1 and then decreases for x>0.1. These variations were attributed to increase of superexchange interaction and spin canting. Furthermore, a model which is based on random distribution of Bi ions in yttrium iron garnet structure was used to achieve the best fit for the Mössbauer patterns. This model explained the effect of Bi substitution on the variation of magnetic hyperfine parameters and also verified the VSM results.

In this study, cerium substituted yttrium iron garnet thin films with nominal formulaY3-xCexFe5O12 and different x value (x = 0,0.1,0.3,0.5,0.7) were fabricated on quartz substrates viasol-gel method and spin coating technique. Samples taken to check physical characteristics. The effect of Ce doping on the structural properties, surface morphology and magnetization of the films were studied respectively by X-ray diffraction analysis (XRD), atomic force microscopy (AFM), and vibrating sample magnetometer (VSM). (AFM) image of annealed samples showed that the thin films had a smooth and continous surface.

In this study, we have prepared nanopowders of Yttrium Iron Garnet (YIG). Phase formation and crystalline structure were investigated by X-ray diffraction (XRD) and IR spectroscopy. Room temperature saturation magnetizations (Ms) of the samples were evaluated using a vibrating samples magnetometer (VSM). The results show that the size of nanoparticles renge from 70 to 250 nm. The results of structure investigation show correlation between Lattice constant and particle size of samples. The Critical size was obtained about 200 nm.

The nanostructured nickel oxide thin films were prepared by dip coating sol – gel method. Three methods (drying with oven, IR and microwave) have used for drying the films. The effect of drying method on the optical, molecular, electrical, structural, and morphology properties of the films were studied by Uv-Visible spectrophotometry, Fourier Transform Infrared spectroscopy, Hall effect, X-ray diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy. Optical constants of nickel oxide thin films were calculated by using Pointwise Unconstrained Minimization Approach. The optical band gap of the films dried by infrared, oven, and microwave methods obtained 3.62, 3.59, and 3.47eV, respectively. The X-ray diffraction patterns of samples show that the film dried by infrared is amorphous while by two other methods are crystalline.

In this research, CaMnO3 powders have been synthesized by solid state reaction and sol-gel methods at calcination temperature of 800°C. Particle size and morphology of the calcined powders have been investigated using XRD and TEM techniques. TEM image showed that the average particle size of the samples, prepared by sol-gel method, is about 85 nm. The optical gap was measured using the absorption spectrum of the powders. The value of the band gap was found for the sample synthesized by sol-gel method is about  3.46eV and that  for sample prepared by solid solution to be about 3.40eV. Also the phase formation of the powders has been studied by Fourier transform infrared (FTIR) spectroscopy. Resistivity measurements of the samples between 300-550°K revealed that resistivity of the samples decreases with increasing temperature.

In this study, a series of copper substituted in nickel–zinc ferrite nanoparticles with composition of Ni0.3Zn0.7-xCuxFe2O4 (where x = 0.1 - 0.6 by step 0.1) were synthesized by sol-gel method. The effect of Cu substitution on phase formation and crystal structure of sample were investigated by X-Ray diffraction (XRD), Thermogravimetry (TG), Differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Moreover the room saturation magnetization of samples was studied by Vibration sample magnetometer (VSM). Hysteresis loops measurements exhibited an increase in the saturation magnetization value (Ms) up to sample with x = 0.3 followed by a linearly decrease. The increases in the coercivety (Hc) with increase in copper content is attributed to the bigger magneto crystalline anisotropy of  Cu2+ ions compared with Zn2+ ions.

In this work, Ce-YIG nanoparticles with nominal composition of Y3-xCexFe5O12 (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were first fabricated by sol-gel method and then the influence of the cerium substitution on the structural and magnetic properties of garnet nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM) and mössbauer spectroscopy. The XRD results showed that the maximum amount of the Ce3+ substitution in YIG structure is x = 0.6. Magnetic measurement shows that room temperature saturation magnetization   of nanoparticles increases up to x = 0.3 firstly and then decreases by increasing Ce content. The variation of saturation magnetization can be explained according to mössbauer studies. The mössbauer analysis showed that due to Ce substitution a and d sublattice split into two pairs of distorted and undistorted sublattice. So reduction in saturation magnetization is disscused.

In this paper, nanoparticles of M- type strontium hexaferrite doped with cobalt SrFe12-xCoxO19 (x= 0-2) were synthesized via sol– gel technique. Structural and morphological properties of the samples were analyzed by X- ray diffraction (XRD), Fourier transform infrared spectroscopy (FT- IR) and scanning electron microscopy (SEM). The XRD results showed that all of the samples of SrFe12-xCoxO19 with x≤0.5 were single-phase. It seems that the Fe3+ ions are substituted by Co2+ ions in the crystallographic sites of the SrFe12O19 structure, but for the samples with x>0.5, the phase of CoFe2O4 is appeared in the samples and suggests that the Co2+ ions also make distinct phase in the samples. The value of the lattice constant a is almost kept unchanged but that of lattice constant c decreases with increasing dopant contents. The FT- IR frequency bands in the range of 560–580 cm-1 and 430– 470 cm-1correspond to the formation of tetrahedral and octahedral clusters of the metal oxides in ferrites, respectively.

In this study, at first the magnetite (Fe3O4) nano particles were prepared by sol-gel method under inert atmosphere using ferric nitrate (Fe (NO3)3.9H2O) and ethylene glycol (C2H6O2) as precursors. In the next stage, magnetite nanoparticles were modified by Sodium citrate under Ar atmosphere. Also zinc oxaid (ZnO) nanoparticles were provided via co-precipitation route and heat treatment using ammonium carbonate and zinc acetate as precursors. The precursor was dried and then calcined at 350oC. Finally with the ZnO and modified Fe3O4 nanoparticles, core–shell system was produced. X-ray diffraction pattern (XRD) considered structure characteristic and the size of crystallites. Morphology and the average size of particles were determined by SEM and TEM electron microscope. The UV absorption spectra show that absorption wavelength value for Fe3O4/ZnO core-shell is increased in comparison with ZnO pure nanoparticles.  FT-IR Spectra indicated the characteristic absorption of Zn–O bond is at 443/81 cm-1 and   Fe–O bond is at 540/20 m-1. Variation of magnetization of samples with respect to the external field was investigated by Vibrating Sample Magnetometer (VSM). Investigation shows that Fe3O4 nanoparticles are super paramagnetic but Fe3O4/ZnO core-shell nanopowders are ferromagnetic. On the other hand, in core-shell system, the amount of remanence or coercivity field have not had a considerable changes with increasing in molar ratio of ZnO to magnetite.     

In this paper, Bi1.66Pb0.34Sr2Ca2Cu3O superconductor powders have been prepared via sol-gel and solid-state reaction methods. The structural and magnetic properties have been studied by the X-Ray diffraction (Fullprof analysis) and magnetic susceptibility measurements. The superconductivity and structural properties of the samples have been compared with the properties of a commercially available sample from Aldrich Company.

The La0.75Sr0.2Mn1-xCoxO3 (0 ≤ X ≤ 1) ¬¬Manganite-Cobaltites are synthesized by sol-gel method and their structural, electrical and magnetic properties are studied. After calcination over 800 ¬ºC, all compounds were crystallized in the perovskite rhombohedral structure (, Space group). Due to nonstochiometery, some traces of the La2O3 phase were appeared in final samples. Resistivity measurements of the samples between 77 and 328 K revealed that resistivity at first decreased and then increased by increasing cobalt content. Also, magnetoresistance results in presence of external fields up to 1.5 T exhibit negative magnetoresistance in all samples. The colossal magneroresistance effect has been observed in all samples except the samples without Mn. Variation of the resistivity and magnetoresistance of the samples with Co content are described based on three following mechanisms: spin scattering, charge compensation and distortion of metal–oxygen-metal bonds. Magnetoresistance behavior of the samples are evaluated based on (1) increased of the double exchange interaction, (2) increased probability of inter-grain tunneling of the carriers, and (3) decreased scattering of carriers from magnetic fluctuations mechanism in the presence of applied field,