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91.
The hyperfine magnetic field at 111Cd impurities substituting iron in the mixed spinels Cd
x
Fe3−x
O4 and Zn
x
Fe3−x
O4 has been determined by means of the Perturbed Angular Correlation technique. Compounds with different concentrations x were investigated as a function of temperature. The possibility of determining the lattice location of probes at octahedral
or tetrahedral sites through the magnitude of the electric field gradient is analyzed. The measured hyperfine magnetic field
at impurities in tetrahedral sites is discussed in terms of the populations of magnetic ions in the nearest neighbor sites.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
92.
N. Rezlescu E. Rezlescu C.‐L. Sava F. Tudorache P. D. Popa 《Crystal Research and Technology》2004,39(6):548-557
Pure and gallium or lanthanum substituted MgCu ferrites, Mg0.5Cu0.5Fe2‐xMxO4 (with x = 0 or 0.2 and M = La or Ga) have been prepared by solid state reaction. Sintering experiments were carried out at different temperatures between 900 and 1100°C. The phase composition and lattice parameters were determined by XRD, while the effect of Ga and La substitutions on the granular structure was studied by SEM. Experimental results revealed that the densification behaviour and some physical properties are in close relation with the structural changes of pure ferrite caused by the presence of La and Ga substitutions. The gallium containing compound, Mg0.5Cu0.5Fe1.8Ga0.2O4, is monophasic and contains a great number of pores, whereas the lanthanum containing compound, Mg0.5Cu0.5Fe1.8La0.2O4, is biphasic and exhibits a high density. The humidity characteristics show that the gallium ion enhances the humidity sensitivity of the MgCu ferrite sintered at 1000°C. This interesting effect is promising for the future of the Ga‐substituted MgCu ferrite to be used as sensitive material for fabrication of ceramic humidity sensors. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
93.
Hailong Yue Congying Ren Guangming Wang Prof. Guihua Li Prof. Rencheng Jin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10575-10584
Transition metal oxides, as one of the most promising anode materials for lithium-ion batteries, often suffer from poor electronic conductivity and serious structural collapse. In this work, oxygen-vacancy-abundant CoFe2O4 and NiFe2O4 deposited on N-doped carbon nanosheets are designed and fabricated through a calcination procedure and a solvothermal strategy using Zn-hexamine coordination frameworks as precursors. The as-prepared NC@CoFe2O4 and NC@NiFe2O4 hybrids display improved cycle performances and rate capacities compared with CoFe2O4, NiFe2O4, and Fe2O3. The enhanced lithium storage performances of NC@CoFe2O4 and NC@NiFe2O4 are attributed to the oxygen vacancies and conductive N-doped carbon nanosheets, which increase the electronic conductivity and electrochemical reaction kinetics. The synthetic process in this work provides a new perspective for designing other high-performance transition metal oxide anodes. 相似文献
94.
CuFe2O4 particles were successfully engineered by a facile sol-gel method. The synthesized products were characterized physically by X-ray diffraction (XRD), scanning electron microscopy (SEM). Besides, the effects of the sintering temperature and the molar ration of citric acid/the total metal cations (CA/MC) on their infrared radiant properties were investigated at the wavelength of 3–5 μm. The highest infrared emission value ca. 0.911 was obtained when the test temperature was conducted at 800 °C, indicating its potential application in infrared heating, infrared coating and drying fields. 相似文献
95.
α‐Aminonitriles as key intermediates for the preparation of α‐amino acid derivatives, amides, diamines, peptides, proteins and heterocycles were synthesized through methylarene oxidation in the Strecker reaction using a unique combination of KI/ZnFe2O4 as the best catalyst and aqueous tert‐butyl hydroperoxide as oxidant. A wide range of amines and methylarenes were converted to the corresponding products. Operational simplicity, short reaction time and recyclability of the catalyst are advantages of this protocol. 相似文献
96.
Polycrystalline Mg1−xZnxFe2O4 (x=0.0–0.6) ferrites have been prepared using solid-state reaction technique. The X-ray diffraction analysis revealed that the samples crystallize in a single-phase cubic spinel structure. The lattice parameter increases linearly with increase in zinc content obeying Vegard's law. The continuous decrease in Curie temperature (Tc) with an increase in Zn content is attributed to the weakening of A–B exchange interaction. Saturation magnetization (Ms) and magnetic moment are observed to increase up to x=0.4, and thereafter decrease due to the spin canting in B-sites. The initial permeability is found to increase with the addition of Zn2+ ions but the resonance frequency shifts towards the lower frequency. 相似文献
97.
98.
M. Elzain H. Widatallah A. Gismelseed K. Bouziane A. Yousif A. Al Rawas I. Al-Omari A. Sellai 《Hyperfine Interactions》2006,168(1-3):1151-1157
The ferrites Mg0.9Mn0.1Cr x Fe2?x O4 ( The ferrites Mg0.9Mn0.1Cr
x
Fe2−x
O4 () were prepared using the conventional double sintering method. The XRD showed that the samples maintain a single spinel cubic
phase. The M?ssbauer measurements were carried out at room and liquid nitrogen temperatures. From the area ratios of the A
and B sites, it was found that the Fe cation population of the A and B sites decreases in proportion to Cr concentration.
The contact hyperfine fields at the A and B sites were found to decrease with increasing Cr contents. This was found to be
in approximate agreement with the results of magnetization measurement. The distributions of Mg and Mn cations versus Cr concentration
were also determined using the M?ssbauer and magnetization results. The Curie temperatures were determined and found to agree
with the reported values. As the Cr contents increases the relative magnetization, was found to increase at low temperatures
and decreases at higher temperatures. 相似文献
99.
Spinel ferrites of the composition Ni1−xCuxFe2O4 (x = 0.0-1.0) have been prepared through the thermal decomposition of their respective impregnated oxalates. The oxalate decomposition process was followed using differential thermal analysis-thermogravimetry techniques (DTA-TG). The synthesized nanocrystallites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The formation of single-phase ferrite is confirmed by XRD. Tetragonal deformation is observed for samples with composition x ? 0.7. The increase in the lattice parameter with increasing Cu content can be explained based on the relative ionic radius. The TEM image shows spherically non-agglomerated particles with an average crystallite size that agrees well with that obtained from XRD. FT-IR studies show two absorption bands (ν1 and ν2) near to 600 and 400 cm−1 for the tetrahedral and octahedral sites, respectively. The hysteresis measurements were done using a vibrating sample magnetometer (VSM). The cation distribution in these compositions is calculated from the magnetization data. With increasing Cu content, the saturation magnetization (Ms) was observed to decrease while the coercivity (Hc) increases. The possible reasons responsible for the composition dependence of the magnetic properties were discussed. The Curie temperature, measured through the temperature dependence of the dc-molar magnetic susceptibility, was found to decrease with increasing Cu content. 相似文献
100.
The Raman spectra of Li0.5Co0.1Fe2.4O4 nanoparticles have been recorded in the spectral range, 400-800 cm−1 at four different particle sizes. X-ray and TEM measurements were done to determine crystal structure and size of the nanoparticles. X-ray diffraction (XRD) shows that the Li0.5Co0.1Fe2.4O4 nanoparticles have an order phase spinel structure without any impurity. The size of the nanocrystal was calculated through XRD patterns and TEM micrographs and it turns out to be 34-42 nm. The Raman spectra of each size nanoparticles show five Raman bands. The most intense Raman band shows a noticeable asymmetrical feature towards lower wavenumber side. A line shape analysis was performed to get the exact spectral parameters of the Raman bands. The intensity of asymmetrical feature keeps on increasing with decreasing the particle size from 42 nm to 34 nm and finally evolved as a new Raman band. The appearance of new band and its intensity response relative to the intensity of the main Raman band as a function of particle size has been explained in terms of electron-phonon coupling. It was observed that the strength of electron-phonon coupling goes on increasing with reducing the particle size. The red shifting of the Raman bands upon reducing the crystalline size is explained in terms of the lattice expansion, which is well supported by the XRD data. 相似文献