共查询到20条相似文献,搜索用时 15 毫秒
1.
S.E. Ziemniak A.R. Gaddipati P.C. Sander 《Journal of Physics and Chemistry of Solids》2005,66(6):1112-1121
The solid solution behavior of the Ni(Fe1−nCrn)2O4 spinel binary is investigated in the temperature range 400-1200 °C. Non-ideal solution behavior, as exhibited by non-linear changes in lattice parameter with changes in n, is observed in a series of single-phase solids air-cooled from 1200 °C. Air-annealing for 1 year at 600 °C resulted in partial phase separation in a spinel binary having n=0.5. Spinel crystals grown from NiO, Fe2O3 and Cr2O3 reactants, mixed to give NiCrFeO4, by Ostwald ripening in a molten salt solvent, exhibited single-phase stability down to about 750 °C (the estimated consolute solution temperature, Tcs). A solvus exists below Tcs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n values of 0.2 and 0.7 at 300 °C. The extrapolated solvus is shown to be consistent with that predicted using a primitive regular solution model in which free energies of mixing are determined entirely from changes in configurational entropy at room temperature. 相似文献
2.
In the present study, nanoferrite of composition Mn0.4Zn0.6In0.5Fe1.5O4 has been synthesized by co-precipitation method. Decomposition of residue at a temperature as low as 200 °C gives the ferrite powder. The ferrite has been, finally, sintered at 500 °C. The structural studies have been made by using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), which confirm the formation of single spinel phase and nanostructure. The dc resistivity is studied as a function of temperature and values found are more than twice those for the samples prepared by the other chemical methods. It is found that the resistivity decreases with increase in temperature. The initial permeability value is found to be higher as compared to the other chemical routes. The initial permeability value is found to increase with increase in temperature. At a certain temperature called Curie temperature, it attains a maximum value, after which the initial permeability decreases sharply. Even at nanolevel, appreciable value of initial permeability is obtained and low magnetic losses make these ferrites especially suitable for high-frequency applications. The particle size is calculated using Scherrer's equation for Lorentzian peak, which comes out between 35 and 49 nm. Possible mechanisms contributing to these processes have been discussed. 相似文献
3.
J. Raittila T. Salminen K. Schlesier 《Journal of Physics and Chemistry of Solids》2006,67(8):1712-1718
Double perovskite Sr2FeMoO6 powders with small crystallite size have been synthesised with citrate-gel method. The starting solution pH was varied between 1.5 and 9.0 resulting in large differences in the phase composition and ordering of B′/B″ sites. The samples prepared at 975 °C had crystallite sizes under 40 nm whereas crystallite sizes of the samples prepared at 1050 °C were between 78 and 239 nm. The XRD patterns were refined with spacegroup I 4/m, which gave good results for both batches, although clearly better results were obtained with monoclinic P 21/n spacegroup for the 975 °C batch. The ordering and the saturation magnetization agreed well with each other after treatment at 1050 °C, but the samples prepared at 975 °C had a strongly reduced saturation magnetization from that given by the ordering. 相似文献
4.
This study has investigated the microstructure and magnetic properties of Fe40Ni38B18Mo4 at various degrees of crystallization from the amorphous state. TEM and XRD studies confirmed that phases forming after crystallization at temperatures around 414 and 522 °C were cubic (Fe, Ni, Mo)23B6 phase and FCC (Fe, Ni) solid solution. The growth behavior and morphology of the nanocrystalline phases have been studied as a function of time and temperature. Nanoparticles were lying in the size range of 10–20 nm and they were stable below 522 °C. Kissinger approach, Ozawa method and Yi Qun Gao method were employed to determine and compare the kinetic parameters of the crystallization processes. A growth mechanism of crystallizing phases was proposed on the basis of these results. Magnetic properties mainly coercivity and saturation magnetization of as-received and heat-treated samples were evaluated. 相似文献
5.
Polyvinyl alcohol (PVA)/ammonium molybdate composite fibers were prepared by using sol-gel processing and electrospinning technique. After calcinations of the above precursor fibers at 500 °C, MoO3 nanofibers with a diameter of 100-150 nm were successfully obtained. MoO3 nanoplatelets and submicron platelets were prepared by further calcinations of the MoO3 nanofibers at 600 and 700 °C. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). A possible growth mechanism for the MoO3 nanofibers and nanoplatelets was suggested. 相似文献
6.
Xuzhen Wang 《Journal of Physics and Chemistry of Solids》2010,71(4):673-676
Carbon nanotubes (CNTs) decorated with magnetite nanoparticles on their external surface have been fabricated by in situ solvothermal method, which was conducted in benzene at 500 °C with ferrocene and CNTs as starting reagents. The as-prepared composites were characterized using XRD, FTIR, SEM and TEM. It has been found that the amount of magnetite nanoparticles deposited on the CNTs can be controlled by adjusting the initial mass ratio of ferrocene to CNTs. The Fe3O4-CNT composites display good ferromagnetic property at room temperature, with a saturation magnetization value (Ms) of 32.5 emu g−1 and a coercivity (Hc) of 110 Oe. 相似文献
7.
R. Thirunakaran A. Sivashanmugam Charles W. Dunnill 《Journal of Physics and Chemistry of Solids》2008,69(8):2082-2090
Pristine spinel LiMn2O4 and LiAlxMn2−xO4 (x=Al: 0.00-0.40) with sub-micron sized particles have been synthesized using fumaric acid as chelating agent by sol-gel method. The synthesized samples were subjected to thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cyclic voltammetry (CV) and galvanostatic cycling studies. The TGA curve of the gel shows several weight-loss regions stepwise amounting to 55% till 800 °C attributed to the decomposition of the precursors. Calcination to higher temperatures (800 °C) yields pure-phase spinel (LiAlxMn2−xO4), as it is evident from the high-intensity XRD reflections matching to the standard pattern. SEM and TEM studies confirm that the synthesized grains are of uniform regular surface morphology. FT-IR studies show stretching and bending vibration bands of Li-O, Li-Al-Mn-O. LiAl0.1Mn1.90O4 spinel was found to deliver discharge capacity of 139 mA h/g during the first cycle with columbic efficiency of 97%. LiAl0.1Mn1.90O4 spinel exhibits the high cathodic peak current indicating better electrochemical performance. Low doping (x=0.1) of Al is found to be beneficial in stabilizing the spinel structure. 相似文献
8.
Brian L. Cushing 《Journal of Physics and Chemistry of Solids》2004,65(4):825-829
Gold-coated nanoparticles of Fe20Ni80 (permalloy) have been synthesized by a microemulsion process. The as-prepared samples consist of ∼5 nm diameter particles of amorphous Fe20Ni80 that are likely encapsulated in B2O3. One or more Fe20Ni80@B2O3 particles are subsequently encapsulated in 8-20 nm gold nanospheres, as determined by TEM and X-ray powder diffraction (XRD) line broadening. The gold shells were found to be under expansive strain. Magnetic data confirm the existence of a superparamagnetic phase with a blocking temperature, TB, of ∼33 K. The saturation magnetization, MS, of the as-prepared, Au-coated sample is ∼65 emu g−1 at 5 K and ∼16 emu g−1 at 300 K. The coercivity, HC, is ∼280 Oe at 5 K. 相似文献
9.
Core-shell-structured LiNi0.5La0.08Fe1.92O4-polyaniline (PANI) nanocomposites with magnetic behavior were synthesized by in situ polymerization of aniline in the presence of LiNi0.5La0.08Fe1.92O4 nanoparticles. The structure, morphology and magnetic properties of samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-vis absorption, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) technique. The results of spectroanalysis indicated that there was interaction between PANI chains and ferrite particles. TEM study showed that LiNi0.5La0.08Fe1.92O4-PANI nanocomposites presented a core-shell structure with a magnetic core of 30-50 nm diameter and an amorphous shell of 10-20 nm thickness. The nanocomposites under applied magnetic field exhibited the hysteresis loops of the ferromagnetic nature. The saturation magnetization and coercivity of nanocomposites decreased with decreasing content of LiNi0.5La0.08Fe1.92O4. The polymerization mechanism and bonding interaction in the nanocomposites have been discussed. 相似文献
10.
Y. Ustinovshikov N. Lomova I. Shabanova 《Journal of Physics and Chemistry of Solids》2008,69(7):1753-1757
High-temperature (above 1200 °C) B2 ordering was experimentally found in the Fe50Co50 alloy with the help of the electron diffraction. Using the X-ray photoelectron spectroscopy method the “ordering-phase separation” transition was shown to lead to changes both in the 3d-electron spectra of the valence band (3d-valence electron localization on Fe atoms increases at phase separation and it decreases at ordering). The investigation of multiplet splitting of the 3s-electron spectra of core-level electrons reveals that magnetic moments on Fe and Co atoms in the Fe50Co50 alloy are larger, when there is the tendency toward ordering, and they are smaller in the case of the tendency toward phase separation. A number of examples are presented, which are indicative of the fact that chemical ordering can influence magnetic ordering by the formation of the respective microstructures and magnetic ordering has no influence on chemical ordering. It can be concluded that the phase transition “ordering-phase separation” takes place both at 730 °C and at the temperature somewhat higher that 1200 °C. 相似文献
11.
Magnetoelectric (ME) nanocomposites containing Ni0.75Co0.25Fe2O4-BiFeO3 phases were prepared by citrate sol-gel process. X-ray diffraction (XRD) analysis showed phase formation of xNi0.75Co0.25Fe2O4-(1−x)BiFeO3 (x=0.1, 0.2, 0.3 and 0.4) composites on heating at 700 °C. Transmission electron microscopy revealed the formation of powders of nano order size and the crystal size was found to vary from 30 to 85 nm. Dispersion in dielectric constant (ε) and dielectric loss (tan δ) in the low-frequency range have been observed. It is seen that nanocomposites exhibit strong magnetic properties and a large ME effect. On increasing Ni0.75Co0.25Fe2O4 contents in the nanocomposites, the saturation magnetization (MS) and coercivity (HC) increased after annealing at 700 °C. The large ME output in the nanocomposites exhibits strong dependence on magnetic bias and magnetic field frequency. The large value of ME output can be attributed to small grain size of ferrite phase of nanocomposite being prepared by citrate precursor process. 相似文献
12.
CoAl0.2Fe1.8O4/SiO2 nanocomposites were prepared by sol–gel method. The effects of annealing temperature on the structure and magnetic properties of the samples were studied by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and Mössbauer spectroscopy. The results show that the CoAl0.2Fe1.8O4 in the samples exhibits a spinel structure after being annealed. As annealing temperature increases from 800 to 1200 °C, the average grain size of CoAl0.2Fe1.8O4 in the nanocomposites increases from 5 to 41 nm while the lattice constant decreases from 0.8397 to 0.8391 nm, the saturation magnetization increases from 21.96 to 41.53 emu/g. Coercivity reaches a maximum of 1082 Oe for the sample annealed at 1100 °C, and thereafter decreases with further increasing annealing temperature. Mössbauer spectra show that the isomer shift decreases, hyperfine field increases and the samples transfer from mixed state of superparamagnetic and magnetic order to the completely magnetic order with annealing temperature increasing from 800 to 1200 °C. 相似文献
13.
Zorica Ž. Lazarević Čedomir Jovalekić Valentin N. Ivanovski Aleksander Rečnik Aleksandra Milutinović Božidar Cekić Nebojša Ž. Romčević 《Journal of Physics and Chemistry of Solids》2014
ZnFe2O4 was prepared by a soft mechanochemical route from two starting combinations of powders: (1) Zn(OH)2/α-Fe2O3 and (2) Zn(OH)2/Fe(OH)3 mixed in a planetary ball mill. The mechanochemical treatment provoked reaction leading to the formation of the ZnFe2O4 spinel phase that was monitored by XRD, TEM, IR and Raman spectroscopy. The spinel phase was first observed after 4 h of milling and its formation was completed after 18 h in both the cases of starting precursors. The synthesized ZnFe2O4 has a nanocrystalline structure with a crystallite size of about 20.3 and 17.6 nm, for the cases (1) and (2), respectively. In the far-infrared reflectivity spectra are seen four active modes. Raman spectra suggest an existence of mixed spinel structure in the obtained nanosamples. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Estimated degree of inversion is about 0.58 for both starting mixtures. The magnetic properties of the prepared ZnFe2O4 powders were also studied. The results show that the samples have a typical superparamagnetic-like behavior at room temperature. Higher values of magnetization in the case of samples obtained with starting mixture (2) suggest somewhat higher degree of cation inversion. 相似文献
14.
Xing Li Changtai Xia Guangqing Pei Xiaoli He 《Journal of Physics and Chemistry of Solids》2007,68(10):1836-1840
Observation of room-temperature ferromagnetism in Fe- and Ni-co-doped In2O3 samples (In0.9Fe0.1−xNix)2O3 (0?x?0.1) prepared by citric acid sol-gel auto-igniting method is reported. All of the samples with intermediate x values are ferromagnetic at room-temperature. The highest saturation magnetization (0.453 μB/Fe+Ni ions) moment is reached in the sample with x=0.04. The highest solubility of Fe and Ni ions in the In2O3 lattice is around 10 and 4 at%, respectively. The 10 at% Fe-doped sample is found to be weakly ferromagnetic, while the 10 at% Ni-doped sample is paramagnetic. Extensive structure including Extended X-ray absorption fine structure (EXAFS), magnetic and magneto-transport including Hall effects studies on the samples indicate the observed ferromagnetism is intrinsic rather than from the secondary impurity phases. 相似文献
15.
Françoise Gilbert Philippe Refait François Lévêque Céline Remazeilles Egle Conforto 《Journal of Physics and Chemistry of Solids》2008,69(8):2124-2130
Magnetic methods are efficient tools in soil and environmental science. But in such natural environments, several magnetic minerals are generally present. So, synthetic standard samples are necessary for calibration of laboratory techniques. The aim of this study was to synthesise goethite free of magnetic impurities (concentration <∼1 μg kg−1) with different crystal sizes. Goethite was prepared by oxidation of aqueous suspensions of Fe(OH)2 precipitates. Final products were characterised by X-ray diffraction, infrared spectroscopy, scanning and transmission electron microscopy and magnetic methods. Goethite could be obtained in the absence of any trace of strong magnetic minerals using FeSO4·7H2O and NaOH as reactants with the following experimental conditions: temperature=45 °C, [FeSO4·7H2O]=0.50 mol L−1, [NaOH]=0.20 mol L−1, stirring speed=760 rpm. The Fe(II) concentration and the stirring speed were varied. It proved possible to modify the size of the goethite crystals by varying the Fe(II) concentration and the stirring speed, but important changes of these parameters induced the formation of other phases, lepidocrocite when the oxidation reaction was drastically accelerated and Fe3O4 when the reaction was slowed down. In any case, for weak magnetic fields, a low-coercivity magnetic mineral saturating at weak magnetic fields was observed. It may correspond to traces of δ-FeOOH or to domains structurally similar to δ-FeOOH inside the multidomainic crystals of δ-FeOOH. 相似文献
16.
Dragica M. Mini? Dušan M. Mini?Tomáš ?ák Pavla RoupcováBohumil David 《Journal of magnetism and magnetic materials》2011,323(5):400-404
Thermal stability and crystallization of the Fe81B12Si4C2 alloy were investigated in the temperature range 25-700 °C by the XRD and Mössbauer analysis. It was shown that on heating the as-prepared amorphous Fe81B12Si4C2 alloy undergoes thermal stabilization through a series of structural transformations involving the process of stress-relieving (temperature range 200-400 °C), followed by a loss of ferromagnetic properties (Curie temperature at 420 °C) and finally crystallization (temperature range 450-530 °C). The process of crystallization begins by formation of two crystal phases: Fe3B and subsequently Fe2B, as well as a solid solution α-Fe(Si). With increase in annealing temperature, the completely crystallized alloy involved only two phases, Fe2B and solid solution α-Fe(Si).XRD patterns established a difference in phase composition and size of the formed crystallites during crystallization depending on the side (fishy or shiny) of the ribbon. The first nuclei of the phase α-Fe3Si were found on the shiny side by XRD after heat treatment even at 200 °C but the same phase on the fishy side of ribbon was noticed after heat treatment at 450 °C. The largest difference between the contact and free surface was found for the Fe2B phase crystallized by heating at 700 °C, showing the largest size of crystallites of about 130 nm at 700 °C on the free (shiny) surface. 相似文献
17.
K. Sadhana 《Journal of magnetism and magnetic materials》2010,322(23):3729-3736
The nanocrystalline Ni0.53Cu0.12Zn0.35Fe1.88O4 and BaTiO3 powders were prepared using Microwave-Hydrothermal (M-H) method at 160 °C/45 min. The as synthesized powders were characterized using the X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The size of the powders that were synthesized using M-H system was found to be ∼30 and ∼50 nm for ferrite phase and ferroelectric phases, respectively. The powders were densified using microwave sintering method at 900 °C/30 min. The ferrite and ferroelectric phases were observed from XRD and morphology of the composites was observed with the Scanning Electron Microscope (SEM).The magnetic hysteresis loops were recorded using the Vibrating Sample Magnetometer (VSM).The frequency dependence of real (μ′) and imaginary (μ″) parts of permeability was measured in the range of 1 MHz-1.8 GHz. The permeability decreases with an increase of BaTiO3 content at 1 MHz. The transition temperature (TC) of ferrite was found to be 245 °C. The TC of composite materials decreases with an increase in BaTiO3 content. 相似文献
18.
Ni-ferrite (NiFe2O4) nanoparticles have been synthesized via a solid state reaction process. Ni and Fe bi-metallic nanoparticles in the form of Ni33Fe67 alloy nanopowder are first synthesized by simultaneous evaporation of the required amounts of pure Ni and Fe metals followed by rapid condensation of the evaporated metal flux into solid state by means of an inert gas, helium, using the process of inert gas condensation (IGC). In order to form the NiFe2O4 structure, as-synthesized samples (Ni33Fe67) are annealed for 12 h in ambient conditions at different annealing temperatures. Structural analyses show that NiFe2O4 starts to form at around 450 °C and gets progressively well defined with increasing annealing temperatures yielding particle with size ranging between 15 and 50 nm. Besides successfully forming NiFe2O4, NiO/Fe3O4 core/shell nanoparticles have also been synthesized by adjusting the annealing conditions. Three different structures, Ni33Fe67, NiO/Fe3O4, and NiFe2O4, obtained in this study are compared with respect to their structural and magnetic properties. 相似文献
19.
In this work zinc ferrite (ZnFe2O4) nanoparticles have been prepared by sol-gel method in two different media, one acidic and another one basic and then annealed at different temperatures from 350 to 800 °C. XRD investigations show that both samples have a single phase spinel structure. Mean crystallite sizes of the samples were calculated, using Scherrer’s formula, which are 13 and 16 nm for the samples prepared in acidic and basic media, respectively. The variation of cation distribution in the samples was estimated by the ratio of (2 2 0) and (2 2 2) intensity diffraction peaks and the results show that as-prepared nanoparticles have different ionic distributions in comparison with that of bulk zinc ferrite. Also the results show that by increasing annealing temperature the ionic distribution of the zinc ferrite nanoparticles tends to that of bulk sample. The magnetic properties of the samples were studied by VSM and the results show that zinc ferrite nanoparticles have a ferrimagnetic behavior. Also the morphology of the powders was examined by TEM. 相似文献
20.
Using a sol-gel processing and electrospinning technique, extrathin fibers of PVA (polyvinyl alcohol)/lithium chloride/cobalt acetate composite were prepared. After calcinations of the above precursor fibers at 600°C, LiCoO2 nanofibers with a diameter of 100-150 nm, were successfully obtained. Measurements of TG/DTA, IR, XRD, Raman, SEM, EDS, respectively, were performed to characterize the properties of the as-prepared materials. We observed a strong correlation between crystalline phase and morphology of the fibers and calcinations temperature. 相似文献