共查询到20条相似文献,搜索用时 62 毫秒
1.
《Materials Research Bulletin》2006,41(9):1612-1621
The simultaneous thermal decomposition and nitridation of [VO(NH2O)2Gly]·H2O complex in NH3 atmosphere at 723–973 K gives the nanocrystalline vanadium nitride (VN) having crystallite size of 8–32 nm. It shows cubic NaCl structure with lattice parameter of a = 4.137 nm. XRD pattern Rietveld analysis program for crystal structure of VN shows the space group-Fm3m. The particle sizes measured by BET and SEM techniques are in the range of 26–100 nm. The particles are spherical and distributed homogeneously and found larger than XRD crystallite size because of agglomeration of crystallites. The fundamental IR absorption of VN material is found at 995 cm−1 which gives the force constant of 634.3 Nm−1. The electrical resistivity and magnetic studies show the superconducting to normal transition (Tc) at 9.2 K. Thermal decomposition of VN is carried out in O2 atmosphere which goes through the formation of an oxynitride (V–Np–Oq) intermediate phase up to 913 K. Finally, nanocrystalline V2O5 is formed at 973 K. The V2O5 has orthorhombic structure with lattice parameters of a = 11.537, b = 3.568 and c = 4.380 Å and the XRD crystallite size of 10 nm. 相似文献
2.
Muhammad Naeem Ashiq Farah Naz Muhammad Aslam Malana Ruqiya Sehrish Gohar Zahoor Ahmad 《Materials Research Bulletin》2012,47(3):683-686
Nano-spinel nickel ferrites doped with Co–Cr at iron and nickel sites are synthesized by the chemical co-precipitation method and are characterized by the XRD, DC electrical resistivity and hysteresis loops measurements. The XRD analyses confirm the formation of single spinel phase and the crystallite size calculated by Scherer's formula is found in the range of 17–19 nm. This crystallite size is small enough to obtain the suitable signal to noise ratio in the high density recording media. The values of electrical resistivity (8.28 × 107 to 29.6 × 107 ohm cm), activation energy (0.545–0.884 eV), saturation magnetization (23.67–33.49 emu g?1) and remanence (12.48–18.67 emu g?1) are increased up to a doping level of x = 0.2 and then starts to decrease. The increase in electrical resistivity, saturation magnetization and remanence suggest that the material with composition Co0.2Ni0.8Fe1.8O4 can be used for applications in microwave devices and high density recording media. 相似文献
3.
《Advanced Powder Technology》2014,25(5):1634-1642
In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO2 nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO2 nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO2 nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450 °C have pure anatase and anatase–rutile mixed structures. The prepared samples having crystallite size between 5 nm and 60 nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TECI), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75 min. 相似文献
4.
《Materials Research Bulletin》2013,48(11):4889-4895
Poly(vinyl pyrrolidone)/CoFe2O4 nanocomposite has been fabricated by a sol–gel auto-combustion method. Poly(vinyl pyrrolidone) was used as a reducing agent as well as a surface capping agent to prevent particle aggregation and stabilize the particles. The average crystallite size estimated from X-ray line profile fitting was found to be 20 ± 7 nm. The high field irreversibility and unsaturated magnetization behaviours indicate the presence of the core–shell structure in the sample. The exchange bias effect observed at 10 K suggests the existence of the magnetically aligned core surrounded by spin-disordered surface layer. The reduced remanent magnetization value of 0.6 at 10 K (higher than the theoretical value of 0.5) shows the PVP/CoFe2O4 nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. 相似文献
5.
Commercial ferrites with high densities are mostly used in the electromagnetic devices, which require high temperature synthesis. In this article the gas-sensing characteristics of pure and Pd-doped MgFe2O4 powder has been discussed. The synthesis has been carried out by using a simple molten salt method. This method facilitates rapid synthesis at comparatively lower temperature enabling formation of nanostructures, suitable for the gas-sensing application. Various physicochemical techniques have been used for the characterization of samples. X-ray diffraction analysis confirmed the single-phase formation of pure and Pd-doped MgFe2O4 having crystallite size 15–20 nm. Pure MgFe2O4 showed highest responses towards liquid petroleum gas (LPG) at 350 °C while, on doping with Pd the highest response shifted towards lower operating temperature of ~200 °C. Pure MgFe2O4 exhibited some response towards 200 ppm of LPG which markedly increased on doping of palladium (Pd). The probable mechanism is proposed to explain the selective response towards LPG. 相似文献
6.
《材料与设计》2015
ZnO nanoparticles were synthesized solvothermally in various diols (ethylene glycol, di(ethylene glycol), tetra(ethylene glycol), 1,2-propanediol, 1,4-butanediol), using basic zinc carbonate (2ZnCO3·3Zn(OH)2) as a precursor for the first time. Since ZnCO3 was sparingly soluble in diols the transformation reaction proceeded at a low reaction rate. Ethylene glycol was found as the most suitable medium among five diols studied yielding the smallest ZnO particles (~ 55 nm) and short reaction time, tr (2 h). Diols with shorter chain length produced smaller ZnO particles. p-Toluene sulfonic acid (p-TSA) acted as a catalyst and reduced tr from 8 h to 2 h in concentration of 0.02 M. Optimum reaction conditions for the synthesis in ethylene glycol were 185 °C and 2 h. At higher p-TSA concentrations (0.04–0.08 M) the size of ZnO particles was reduced from 500–800 nm to 50–100 nm and crystallite size to 25–30 nm. Benzene sulfonic acid (BSA) and inorganic bases (LiOH, NaOH, and KOH) also showed catalytic activities. Raman and photoluminescence spectroscopies revealed high concentration of defects on ZnO surface causing the emission of visible light and giving this type of ZnO higher potential in various (opto)-electronic application in comparison to Zn(II) acetate based ZnO. 相似文献
7.
Structural phase analysis,band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles
This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO2 (titania) nanoparticles (NPs) synthesized by employing acid modified sol–gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV–visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer’s formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO2 in anatase structure in both pure and Co doped TiO2 NPs. The most intense Raman active Eg peak of TiO2 NPs shifted to higher energy on doping. Both UV–visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect. 相似文献
8.
The supermalloy (Ni79Fe16Mo5) nanostructured powder with average crystallite size of about 8 nm was prepared by high energy milling. The obtained powders were characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and vibration sample magnetometer. The results showed that the coercivity and the saturation magnetization reach about 8 Oe and 75 emu/g at 96 h and become approximately 1 Oe and 85 emu/g after a suitable heat treatment, respectively. The magnetic measurements confirmed that the supermalloy soft magnetic nanostructure powder was produced by mechanical alloying followed by a post heat treatment. The results revealed that a small amount of Mo element remain in the system up to 96 h due to (i) high fusion temperature, Tf = 2893 K, (ii) high mechanical hardness, (iii) low solubility of Mo into Ni at low temperatures in mechanical alloying conditions. 相似文献
9.
《Advanced Powder Technology》2014,25(1):457-461
In this study, nano-crystalline Ni0.6−xCuxZn0.4Fe2O4 ferrite (0.0 ⩽ x ⩽ 0.5) with grain sizes of 16–38 nm have been prepared through a novel method using gelatin. The proper calcination temperature for the precursors which corresponding to the ferrites formation is estimated through thermal analysis measurement. X-ray diffraction patterns confirmed the formation of single phase cubic spinel structure. The grain size was estimated using transmission electron microscopy (TEM) technique. The lattice constant hardly changed with increasing copper concentration while the crystallite size increases. Fourier transform infrared spectra (FT-IR) indicate that the portion of Fe3+ ions at the tetrahedral sites move to the octahedral sites as some of the substituted Cu2+ ions get into the tetrahedral sites. The effect of Cu-substitution on the magnetic properties was studied through the temperature dependence of the molar magnetic susceptibility. The Curie temperatures (TC) were found to decrease with increasing the Cu concentration while molar magnetic susceptibilities remain constant. 相似文献
10.
Chromium doped titanium dioxide (TiO2) nanocrystal films with various doping concentration have been successfully prepared by a sol–gel dip-coating process. These films have been characterized by XRD, XPS, AFM, and UV–vis absorption spectroscopy. It is found that Cr doping can effectively reduce the transition temperature of anatase to rutile phase as well as the grain size. The absorption edges of TiO2 thin films shift towards longer wavelengths (i.e. red shifted) from 375 nm to about 800 nm with increasing Cr concentration, which greatly enhances TiO2 nano-materials on the absorption of solar spectrum. The appearance of UV–vis absorption features in the visible region can be ascribed to the newly formed energy levels such as Cr 2p level and oxygen vacancy state between the valence and the conduction bands in the TiO2 band structure. The enhancement of the photocatalytic properties is observed for Cr-doped TiO2 thin film. 相似文献
11.
Indium oxide nanoparticles of ~12 nm were synthesized by a simple chemical route using indium(III) nitrate. Nanoparticles are formed after calcining the dried precursor in air at 400 °C for 10 h. TEM analysis showed that the morphology and size of the In2O3 samples were affected by ultrasonication. FTIR and Raman studies reveal that the nanoparticles are single-phase cubic structure of In2O3. NEXAFS study was used to quantify the Indium and oxygen valence state. Magnetic behavior of indium oxide nanoparticles was found to be diamagnetic. UV spectra show a weak band at ~308 nm corresponds to optical band gap energy of 4.03 eV. 相似文献
12.
M. Parthibavarman V. Hariharan C. Sekar 《Materials science & engineering. C, Materials for biological applications》2011,31(5):840-844
Tin oxide hexagonal-shaped nanodiscs (SnO) and spherical nanoparticles (SnO2) have been prepared by using a simple household microwave irradiation method with an operating frequency of 2.45 GHz. This technique permits us to produce gram quantity of homogeneous nanoparticles in just 10 min. The crystallite size was evaluated from powder X-ray diffraction (XRD) studies and was in the 20 to 25 nm range. Transmission electron microscopy (TEM) analysis showed that the as prepared SnO form as hexagonal-shaped nanodiscs and upon subsequent annealing at 500 °C for 5 h in air, the SnO gets converted to spherical-shaped nanoparticles of SnO2. The SnO2 sample shows good sensitivity towards the relative humidity. The calculated response and recovery time were found to be 32 s and 25 s respectively. These results indicate promising applications of SnO2 nanoparticles in a highly sensitive environmental monitoring and humidity controlled electronic devices. The samples were further subjected to thermal analyses (TG–DTA) and UV–VIS diffusion reflectance spectroscopy (DRS) studies. 相似文献
13.
《Advanced Powder Technology》2014,25(1):423-429
This investigation aims to produce TiC–Al2O3 nanocomposite by reducing rutile with aluminum and graphite powder via a mechanochemical process. The effect of milling time on this process was investigated. The characterization of phase formation was carried out by XRD and SEM. Results showed that after a 10 h milling, the combustion reaction between Al, TiO2 and C was started and promoted by a self-propagation high temperature synthesis. Extending the milling time to 20 h, the reaction was completed. The XRD study illustrated after a 20 h milling, the width of TiC and Al2O3 peaks increased while the crystallite sizes of these phases decreased to less than 28 nm. After annealing at 800 °C for 1 h in a tube furnace, TiC and Al2O3 crystallite sizes remained constant. However, raising the annealing temperature to 1200 °C caused TiC and Al2O3 crystallite size to increase to 49 nm and 63 nm, respectively. No new phase was detected after the heat treatment of the synthesised TiC–Al2O3 nanocomposite. 相似文献
14.
Mechanical alloying is a suitable method for producing copper based composites. Cu–TiO2 composite was fabricated using high energy ball milling and conventional consolidation. Ball milling was performed at different milling durations (0–24 h) to investigate the effects of the milling time on the formation and properties of produced nanostructured Cu–TiO2 composites. The amount of the TiO2 in the final composition of the composite assumed to be 0, 1, 3, 5 and 7 wt%. The milled composite powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy to investigate the effects of the milling time on the formation of the composite and its properties. Also hardness, density and electrical conductivity of the sintered specimen were measured. High energy ball milling causes a high density of defects in the powders. Thus the Cu crystallite size decreases, generally to less than 50 nm. The maximum hardness value (105 HV) of the sintered compacts belongs to Cu–5 wt%TiO2 which has been milled for 12 h. 相似文献
15.
Nanocrystalline sulfated zirconia powder was prepared by a non-alkoxide sol–gel route using acidic condition (pH 1–2). The samples had superfine crystallites and pure tetragonal phase at 700 °C. Zr(acac)4 was used as zirconium precursor due to a better retention of sulfate species and H2SO4 0.5 M was used as sulfating agent. Fourier transform infrared (FT-IR) spectra have shown Zr–O–Zr and sulfate bonds. Crystal phase and crystallite size have been determined by X-ray Diffraction (XRD) analysis. Besides, the morphology of the samples has been investigated by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The optical properties of the samples have been analyzed using photoluminescence (PL) spectroscopy, too. All the analyses consistently have shown fairly uniform nanoparticles (calcined at 600 and 700 °C) with very small size and pure tetragonal phase with crystallite size between 5 and 10 nm. 相似文献
16.
The dependence of the crystallite size and the band tail energy on the optical properties, particle shape and oxygen vacancy of different ZnO nanostructures to catalyse photocatalytic degradation was investigated. The ZnO nanoplatelets and mesh-like ZnO lamellae were synthesized from the PEO19-b-PPO3 modified zinc acetate dihydrate using aqueous KOH and CO(NH2)2 solutions, respectively via a hydrothermal method. The band tail energy of the ZnO nanostructures had more influence on the band gap energy than the crystallite size. The photocatalytic degradation of methylene blue increased as a function of the irradiation time, the amount of oxygen vacancy and the intensity of the (0 0 0 2) plane. The ZnO nanoplatelets exhibited a better photocatalytic degradation of methylene blue than the mesh-like ZnO lamellae due to the migration of the photoelectrons and holes to the (0 0 0 1) and (0 0 0 −1) planes, respectively under the internal electric field, that resulted in the enhancement of the photocatalytic activities. 相似文献
17.
H.E. Esparza-Ponce J. Hernández-Borja A. Reyes-Rojas M. Cervantes-Sánchez Y.V. Vorobiev R. Ramírez-Bon J.F. Pérez-Robles J. González-Hernández 《Materials Chemistry and Physics》2009,113(2-3):824-828
An ammonia-free chemical-bath deposition was used to obtain CdSe thin films on glass substrate. The materials used in the chemical bath were cadmium chloride complexed with sodium citrate and sodium selenosulphate. The preparation conditions, especially the starting solution characteristics, such as concentration of dissolved materials, temperature, pH value as well as deposition time and immersion cycles were optimized to obtain homogeneous stoichiometric films with good adherence to the glass substrate. The films thickness was in the range of 400–500 nm with a growing time of 4 h. The material obtained was characterized by optical absorption, SEM with the energy dispersive X-ray analysis (EDS) and X-ray diffraction. The films obtained at bath temperatures of 70 and 80 °C had the hexagonal structure (of wurtzite type), with crystallite size of about 20 nm. Room temperature deposition results in films with the cubic structure and crystallite size of about 4 nm. From optical transmission data, an energy gap equal to 1.88 eV was found. The material is interesting for applications in hybrid systems for solar energy conversion. 相似文献
18.
Radheshyam Rai Seema Sharma Rashmi Rani M.A. Valente Andrei L. Kholkin 《Materials Letters》2011,65(17-18):2703-2706
Polycrystalline samples of (1 ? x) Na0.5K0.5NbO3–(x) GdFeO3 (designated as NKN–GF) (x = 0.01, 0.02, 0.04, 0.6 and 0.10), were prepared by a conventional solid-state reaction technique. Preliminary structural studies at room temperature suggest that compounds are formed in a single perovskite phase. Compositions with x = 0.02–0.04 possess orthorhombic structure while for x = 0.06–0.10 show tetragonal structure. The diffraction peaks shift slightly to a higher angle with increasing concentration of x. The ferroelectric phase-transition of these materials, shows a shift in the transition temperature towards the higher-temperature side with increased GF concentration. The magnetization increases with the increase in GF content which is clearly perceptible in the evolution of hysteresis loops indicating that GdFeO3 doped NKN has introduced ferromagnetic contribution. This may be attributed to variation in the oxygen stoichiometry, doping at different crystallite sites and change in the magnetic anisotropy. 相似文献
19.
In this paper, the polyol process, a catalyst free, non-aqueous, and electroless process, is developed to deposit the nanostructured NixCo100 ? x magnetic films on aluminum nitride (AlN) substrate. Nickel (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate were reduced by ethylene glycol (EG) at 180 °C, and the reduced Ni and Co nanostructures were deposited on the AlN substrate merged in boiling EG for 60 min. The elongated nanostructures in the films are detected through the scanning electron microscopy (SEM). Interestingly, some of the elongated nanostructures are pointing out of the substrate. It indicates that the component ratio of Ni and Co in the films is different with the starting precursor molar ratio. The film thickness increases from 1 to 1.8 μm when the atomic ratio of Co (at.%) in the film increased from 44.6% to 70.8%. Furthermore, it is found that the crystallite size decreases from 44 to 25 nm with increasing Ni (at.%). In addition, the magnetic properties have been analyzed through vibrating sample magnetometer (VSM) at room temperature. The results show that the films have the perpendicular preferred anisotropy. The anisotropy field (HK) for the Ni50Co50 is about 4.75 kOe, which is possibly caused by the assembled direction of the elongated nanostructures. 相似文献
20.
Pornapa Sujaridworakun Siriporn Larpkiattaworn Sarawut Saleepalin Thanakorn Wasanapiarnpong 《Advanced Powder Technology》2012,23(6):752-756
The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO2:Na2CO3 at 850 °C. Then, the powder was dissolved in 5 M H2SO4 solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m2/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO2:Na2CO3 and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation. 相似文献