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1.
The bulk samples of Mn‐doped ZnO were synthesized with the nominal compositions Zn1‐xMnxO (x = 0.02, 0.05, 0.10, 0.15) by the solid‐state reaction and sol‐gel methods. In both the methods the samples were finally sintered at ∼700 °C in air. The X‐ray diffraction (XRD) studies of the samples synthesized by the solid‐state reaction method exhibit the presence of wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples, suggesting that doped Mn ions sit at the regular Zn sites. However, same studies spread over the samples with Mn content ≥5% and synthesized by the sol‐gel method reveal the occurrence of some secondary phase in addition to the majority wurtzite phase. The magnetic measurements by vibrating sample magnetometer (VSM) clearly indicate ferromagnetic interaction at room temperature in all the samples. The Curie temperatures (Tc) and magnetization vary with concentration of Mn ions in the samples. However, the samples synthesized by sol‐gel method were found to have lower Tc values and also lower magnetization as compared to the corresponding samples synthesized by solid‐state reaction method. It could possibly be due to the presence of antiferromagnetic islands and smaller crystallite sizes in the samples prepared by sol‐gel method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
Spindle‐shaped α‐FeOOH nanocrystals were facilely synthesized using a poly (vinyl pyrrolidone) (PVP)‐assisted route under hydrothermal conditions. The chemical compositions and morphol‐ogies of the as‐prepared samples were characterized in detail by X‐ray power diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The experimental results reveal that these spindle‐shaped α‐FeOOH nanocrystals have self‐organized into assemblies with hierarchical nanostructures. The crucial roles of PVP in the hydrothermal synthesis of hierarchical α‐FeOOH nanostructures were discussed. The possible formation mechanism was also suggested. Moreover, the spindle‐shaped α‐Fe2O3 nanocrystals could be easily obtained after calcining the α‐FeOOH prepared by the PVP‐assisted hydrothermal process. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
We report on the structural and magnetic properties of the polycrystalline samples of Zn1‐xCoxO (x = 0.05, 0.10 and 0.15) synthesized via sol‐gel route. The air sintered samples of all compositions exhibit paramagnetic behaviour at room temperature, on the other hand the same samples on annealing in Ar/H2 atmosphere show room temperature ferromagnetism (RTFM) with enhanced magnetization. The value of magnetization increases with the Co concentration (x) in both the air sintered and Ar/H2 annealed samples. The observed ferromagnetism in the Ar/H2 annealed Zn1‐xCoxO (x = 0.05, 0.10 and 0.15) samples is attributed to the presence of Co nanoclusters as detected by XRD and FESEM‐EDAX. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
The present study reports the synthesis of Ce0.8Sm0.2O1.9 solid electrolyte by a novel proteic sol‐gel method which uses gelatin as polymerizing agent. The as‐synthesized powder material was calcined at 700 °C for 2 h, with X‐ray diffraction revealing a single cubic phase with lattice parameter a = 0.5435 nm and theoretical density of 7.144 gcm‐3. The average crystallite size is 12 nm, as determined by the Scherrer equation. Impedance spectroscopy revealed a larger resistive contribution of the grain boundaries than that from grain bulk, which, due to its lower activation energy, tends to dominate the total conductivity above 650 °C. The total conductivity is in line with literature data for ceramics of the same composition prepared by various methods, thus confirming the potential of the proteic sol‐gel method as a green, low cost alternative synthetic route to prepare ceria‐based solid electrolytes.  相似文献   

5.
Different morphologies of single‐crystalline orthorhombic phase bismuth sulfide (Bi2S3) nanostructures, including sub‐microtubes, nanoflowers and nanorods were synthesized by a urea‐assisted hydrothermal method at a low temperature below 120 °C for 12 h. The as‐synthesized powders were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and UV‐vis spectrophotometry. The experimental results showed that the sulfur sources had a great effect on the morphology and size of the resulting powders. The formation mechanism of the Bi2S3 nanostructures with different morphologies was discussed. All Bi2S3 nanostructures showed an appearance of blue shift relative to the bulk orthorhombic Bi2S3, which might be ascribed to the quantum size effect of the final products. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
The mixed oxide (Gd1‐xYx)2O3 (0.0 ≤ x ≤ 1.0) were synthesized, as powder and thin film, by a sol‐gel process. X‐ray diffraction data were collected and crystal structure and microstructure analysis were performed using Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. The cationic distribution, Gd3+ and Y3+, over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be random for all values of (x). The lattice parameter is found to vary linearly with the composition (x). Replacing Gd3+ and Y3+ by each other introduces a systemic decrease in the x‐coordinate of cation position (24d) and slight changes in the oxygen coordinates. Crystallite size and microstrain analysis is performed along different crystallographic directions and anisotropic changes are found with the composition parameter (x). The average crystallite size ranges from 75 to 149 nm and the r.m.s strain from 0.027 to 0.068 x10‐2. Textured Gd1.841Y0.159O3 (400) buffer layers, with a high degree of alignment in both out‐plane and in‐plan, are successfully grown on cube textured Ni (001) tape substrates by sol–gel dip coating process. The resulting buffer layers are crack‐free, pinhole‐free, dense and smooth. YbBa2Cu3O7‐x (YbBCO) thin film could be (00l) epitaxially grown on the obtained buffer layer using sol–gel dipping technique. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
The electrical, magnetic, and structural features of bismuth manganite (BM), e.g., BiMnO3, and bismuth ferrite (BF), e.g., BiFeO3, are reviewed. Induced multiferroicity and enhanced magnetoelectric coupling are required for various modern device applications. BM and BF were synthesized using standard high-temperature sintering and processes such as sol–gel, hydrothermal, or wet chemical methods combined with annealing. The size and morphology of the nanoscale particles were controlled, although they were usually inhomogeneous. BF exhibits structurally stable antiferromagnetic (AFM) and ferroelectric (FE) phases in wide temperature ranges. Ferromagnetic (FM) order was induced in a thick shell around the AFM core of the nanoscale BF particles, which was attributed to a size effect related to surface strains and disorder. BM exhibited both structurally stable and unstable phases. The BiMnO3, Bi12MnO20, and BiMn2O5 structures are nonferroelectric. The perovskite BiMnO3 form was synthesized under high hydrostatic pressure. FM order occurs in BM at low temperatures. Bi(MnFe)O3 solid solution samples exhibited competition between AFM and FM ordering. Doping can decrease the content of unavoidable secondary phases. Doping in the Bi ion sublattice can stabilize the crystal lattice owing to local strains caused by the difference in ionic radius between Bi and the dopant. Doping in the Fe and Mn sublattices affects the electrical features. The main achievement of substitution with tetra- and pentavalent ions is compensation of the oxygen vacancies. In turn, leakage current suppression enables switching of FE domains and polarization of the samples. A significant enhancement of magnetoelectric coupling was observed in composites formed from BF and other FE materials. The leakage currents can be diminished when an insulator polymer matrix blocks percolation. The potential applicability is related to enhanced magnetoelectric coupling. The constructed devices meet the size effect limitations for FE and FM ordering. Resistive switching suggests possible use in nonvolatile memories and gaseous sensors. The sensors can be used for hydrophones and for photovoltaic and photoluminescence applications, and they can be constructed from multiphase materials. Bulk multiferroic solid solutions, composites, and nanoheterostructures have already been tested for use in sensors, transducers, and read/write devices for technical purposes.  相似文献   

8.
Due to size‐dependent catalytic selectivity, the size and special morphology are of great importance to applications of TiO2. The synthesis method of size and morphology control has been in need of innovation. In this study, TiO2 nanoparticles(TiO2‐NPs) with well‐defined morphology and homogenous size were synthesized using a novel method, in which bamboo substrate, dielectrophoresis (DEP) technology and a sol‐gel process were combined(substrate/ DEP/ sol‐gel). Powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the TiO2‐NPs. Further study showed that, with this combined method, the size and the uniformity of TiO2‐NPs can be controlled by changing the voltage of DEP. The number and arrangement of TiO2 nanorods can be controlled by changing the voltage. Substrate/ DEP/ sol‐gel proved to be an efficient way to form special morphologies of TiO2‐NPs. A visible‐light catalytic activity experiment showed that among three preparation methods, the substrate/ DEP/ sol‐gel method made TiO2‐NPs with the highest catalytic activity for degradation of methyl orange. TiO2‐NPs produced by the DEP/ sol‐gel process presented higher catalytic activity than TiO2‐NPs produced by only a sol‐gel process.  相似文献   

9.
Nanocrystalline particles of Co2+doped lithium aluminate (Co2+:LAO) and Ni2+‐doped lithium aluminate (Ni2+:LAO) were synthesized by sol–gel method. The crystalline nature and particle size of the samples were characterized by X‐ray diffraction analysis (XRD). The morphology and the presence Co2+ and Ni2+ in the synthesized samples were analyzed by scanning electron microscope (SEM) and energy dispersive X‐ray analysis (EDAX). The presences of functional groups in the samples were analyzed using FT‐IR analysis. The optical absorbance of the synthesized samples were observed using UV absorption spectral analysis. The frequency dependent dielectric behaviour of the synthesized nano materials was analyzed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
Using the ionic liquid (IL), 1‐butyl‐3‐methyl‐imidazole tetrafluoroborate, and the precursor Cu7Cl4(OH)10·H2O, series of phase‐manipulable Cu‐based nanomaterials were synthesized by hydrothermal and microwave assisted routes, respectively. The structural characters of the as‐prepared CuO, CuO/Cu2O composites and pure Cu nanoparticles were investigated by XRD, SEM, TEM and HRTEM, and their surface photovoltaic properties were studied by surface photovoltage spectra. Via hydrothermal route Cu2+ ions were found to be reduced gradually into Cu+ and subsequently Cu0 with increasing the IL, and various phase ratio of CuO, Cu2O and Cu composite nanosheets and pure Cu nanoparticles were obtained. This implies that the IL could function as both a reductant in the oxygen‐starved condition and a template for the nanosheet products. The 1H‐NMR result of the IL supports it being a reductant. In microwave assisted route, however, only monoclinic single crystalline CuO nanosheets were obtained, which indicates the IL being a template only in oxygen‐rich condition. Therefore, the crystal phase, composition and morphology of the Cu‐based products could be controlled by simply adjusting the quantity of the IL and oxygen in solution routes. The molecular structure of the IL after oxidation reactions was investigated by 1H‐NMR and a possible reaction mechanism was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
Mixed ZnO‐ZrO2 films have been obtained by sol‐gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary from 400 °C to 750 °C) on their structural properties has been studied. The structural behavior has been investigated by the means of XRD and FTIR techniques. The results revealed no presence of mixed oxide phases, the detected crystal phases were related to the hexagonal ZnO and to crystalline ZrO2. The sol‐gel ZnO‐ZrO2 films showed polycrystalline structure with a certain degree of an amorphous fraction. The optical transmittance reached 91% and it diminished with increasing the annealing temperatures. The optical properties of the sol‐gel ZnO‐ZrO2 films, deposited on glass substrates are excellent with high transparency and better then those of pure ZrO2 films, obtained at similar technological conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
Mn‐doped ZnO were synthesized by solid state reaction and sol‐gel method respectively. It was found that samples synthesized by solid state reaction containing Mn2O3 and MnO2 are a mixture of ferromagnetic and paramagnetic phases. Contrary, samples without second phases were found to be paramagnetic at room temperature. According to previous report, interface effects between Zn‐rich Mn2O3 and MnO2 interfaces may be the origin of the ferromagnetic behavior observed in our samples prepared by solid reaction, so the alloy of Zn1−xMnxO may be paramagnetic at room temperature. Prepared by sol‐gel technique, the samples without second phases in the XRD patterns are also room‐temperature paramagnetic. Therefore we believe that the magnetism of Zn1−xMnxO is paramagnetic at room temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
Octahedral Fe3O4microcrystals were synthesized using a triethanolamine‐assisted route under hydrothermal conditions. The chemical compositions and morphologies of the as‐prepared samples were characterized in detail by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). During the hydrothermal process for the preparation of Fe3O4 octahedra, the possible mechanism was discussed to elucidate the formation of the octahedral Fe3O4microcrystals. Triethanolamine and hydrazine hydrate play important roles in the formation of the final products. The magnetic property of sample was evaluated on a vibrating sample magnetometer (VSM) at room temperature. The values of saturation magnetization and coercivity of octahedral Fe3O4are about 103 emu/g and 157 Oe, respectively. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
Dendrite and platelet‐like α‐Fe2O3 microcrystals were synthesized by the oxidation reaction of K4Fe(CN)6and NaClO3 through a simple hydrothermal method. The structures and morphologies of the as‐prepared samples were characterized in detail by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experiment results show that NaOH played an important role in controlling the morphology of the final products. The possible mechanism was discussed to elucidate the formation of different morphologies of the α‐Fe2O3 microstructures. Besides, the magnetic property of the dendrite α‐Fe2O3 microstructure was characterized by a vibrating sample magnetometer (VSM). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
We synthesized mercuric iodide and bismuth tri‐iodide nanoparticles by suspension in octadecene, from Hg(NO3)2.H2O and I2, and from Bi(NO3)3.5H2O and I2, respectively. The best synthesis conditions were 2 h at 70‐80 °C, followed by 10 min at 110 °C for mercuric iodide nanoparticles, and 4 h at 80‐110 °C, followed by 10 min at 180‐210 °C for bismuth tri‐iodide ones. Nanoparticles were then washed and centrifuged with ether repeatedly. Compounds identity was confirmed by X‐ray diffraction (XRD) and energy dispersive spectrometry (EDS). We found shifts of the X‐ray diffraction maxima for nanoparticles of both compounds. We characterized the nanoparticles by transmission (TEM) and scanning (SEM) electron microscopy. We obtained disk‐like and squared mercuric iodide nanostructures, 80‐140 nm and 100‐125 nm in size respectively. We also obtained rounded and rod‐like bismuth tri‐iodide nanoparticles, 30‐500 nm in size. Acetonitrile and isopropanol suspensions of mercuric iodide nanoparticles, and acetonitrile suspension of bismuth tri‐iodide nanoparticles exhibited peak maxima shifts in their UV‐Vis spectra. We synthesized for the first time mercuric iodide and bismuth tri‐iodide nanoparticles by the suspension method, although we have not yet obtained uniform shape and size distributions. They offer interesting perspectives for crystalline film nucleation and for improving current applications of these materials, as well as for opening new ones. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
Zinc sulfide (ZnS) microspheres were synthesized by a self‐template hydrothermal route using thiourea as sulphur source. The formation of these hollow spheres was mainly attributed to the oriented aggregation of ZnS nanocystals around the gas‐liquid interface between gas (H2S, NH3, or CO2) and water followed by an Ostwald ripening process. The gas bubbles of H2S, NH3, or CO2 produced during the reaction might play a soft‐template to form ZnS hollow microspheres. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), electron diffraction (ED), and photoluminescence (PL). The crystal structure of prepared ZnS microspheres is hexagonal phase polycrystalline. The average microspheres diameter is 1.5 ‐ 6 µm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
The Rare earth mixed oxides Dy2‐xHox O3 (0.0 ≤ x ≤ 2.0) solid solution was synthesized by a sol–gel process. X‐ray diffraction (XRD) data were collected and crystal structure and microstructure analyses were performed applying Rietveld refinement method. Infrared and Raman spectroscopy were used to define the microstructure and to locally probe the structure of the samples. The cationic distribution over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be randomly. The crystallite size and microstrain as well as Raman modes positions are influenced by Ho3+ concentration. The apparent size is isotropic but significant anisotropy is found for the microstrain with its largest value along the crystallographic direction [h00]. Inspite the single phase solid solution confirmed by Rietveld analysis for all samples, Raman spectra detected the coexistence of two phases; cubic and distorted monoclinic of too small amount or highly disordered, i.e. amorphous like, to be detected by XRD. The result indicates the ability of Raman spectroscopy to detect minor phases in solid solutions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
Glass–ceramics with the composition 2Fe2O3.1ZnO.1MgO.96SiO2 [4ZnMgFe] and 2Fe2O3.2ZnO.3MgO.93SiO2 [7ZnMgFe] (mol%) were prepared using the sol–gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron diffraction (ED) and Mössbauer spectroscopy (MS) were used to investigate the glass–ceramics structure. The samples contain ferrite nanoparticles embedded in a glass matrix. However, zinc ferrite nanoparticles seems to be the preferential crystalline phase formed. The amount of ferrite particles depends on treatment temperature and sample composition. The Mössbauer spectroscopy measurements show that ferrite nanoparticles can exhibit a ferrimagnetic behaviour combined with superparamagnetism.  相似文献   

19.
Flower‐like self‐organized crystalline ZnO architectures were obtained through a facile and controlled hydrothermal process. As‐synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), electron diffraction and UV‐Vis spectroscopy. XRD and electron diffraction results confirmed the obtained materials are pure wurtzite ZnO. The effects of different ratios of starting materials and solvent on the morphologies of ZnO hydrothermal products were also evaluated by SEM observations. It is suggested that the use of water, rather than ethanol as the solvent, as well as employing a precursor of Zn(Ac)2 and 2NaOH (v/v) in hydrothermal reactions are responsible for the generation of specific flower‐like self‐assembled ZnO structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
A three‐dimensional polyoxovanadate formulated as HV3O8·H2O has been synthesized by hydrothermal method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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