共查询到20条相似文献,搜索用时 31 毫秒
1.
Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on FexCu1−xBa2YCu2O7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuOx chains have fivefold-oxygen coordination. These are important reasons for the enhancement of Tc in the HP-samples. 相似文献
2.
Sven-Ulf Weber Thorsten M. Gesing Götz Eckold Reinhard X. Fischer Fred-Jochen Litterst Klaus-Dieter Becker 《Journal of Physics and Chemistry of Solids》2014
The Bi2(FexGa1−x)4O9 oxide solid solution possessing a mullite-type structure has been investigated by 57Fe Mössbauer spectroscopy in dependence of composition (0.1≤x≤1) and temperature (293≤T/K≤1073). The spectra have been fitted with two doublets for tetrahedrally and octahedrally coordinated high-spin Fe3+ ions, respectively. The experimental areas of the subspectra were used to determine the distribution of iron on the two inequivalent structural sites. The fraction of iron cations occupying the octahedral site is found to increase with decreasing Fe content and the cation distribution is almost independent of temperature. The unusual temperature dependence of the quadrupolar splitting, QS, observed for the octahedral site with dQS/dT>0 is discussed in connexion with structural data for Bi2Fe4O9. The temperature dependence of Mössbauer isomer shifts and signal intensities is examined in the context of local vibrational properties of iron on the two inequivalent sites of the mullite-type lattice structure. 相似文献
3.
O. Mounkachi M. Belaiche A. Benyoussef M. Sajieddine 《Solid State Communications》2011,151(13):938-942
Polycrystalline Zn0.6Cu0.4Fe2O4 ferrites have been prepared using a solid-state reaction technique. Their structural and magnetic properties have been studied, using X-ray diffraction and Mössbauer and magnetic measurements. These results have been compared to a more general theoretical study, on ZnxCu1−xFe2O4, based on mean field theory and high-temperature series expansions (HTSE), and extrapolated with the Padé approximant method. The nearest neighbour super-exchange interactions for the intra-site and the inter-site of ZnxCu1−xFe2O4 spinel ferrites, in the range 0≤x≤1, have been computed using the probability approach, based on Mössbauer data. The Curie temperature TC is calculated as a function of Zn concentration. The theoretical results obtained are in good agreement with the experimental results obtained by magnetic measurements. 相似文献
4.
J.M. Gaudet T.D. Hatchard S.P. Farrell R.A. Dunlap 《Journal of magnetism and magnetic materials》2008
Alloys of Fe–Ga with starting compositions of 17, 19, 21, 23, and 25 at% Ga and Fe81Ga17Z2 (Z=Si, Sn) have been prepared by mechanical alloying. Samples were milled in a SPEX Model 8000 mill with a ball to sample weight ratio of about 4:1. Phase formation as a function of milling time has been investigated for the 19 at% Ga sample and suggests that milling times of 12 h produce fully alloyed samples. Alloys have been studied by electron microprobe, X-ray diffraction, vibrating sample magnetometery and 57Fe Mössbauer effect spectroscopy. Fully milled powders have measured compositions of Fe100−xGax with x=15.7, 17.0, 19.0, 22.4, and 24.0 and Fe83.1Ga15.2Z1.7 (for both Z=Si and Sn). X-ray diffraction showed the presence of a disordered bcc phase with no indication of an ordered D03 phase. However, the latter is difficult to observe with X-ray diffraction because of the low intensity of the fcc superlattice peaks. A bimodal Fe hyperfine field distribution as obtained from Mössbauer effect spectra indicated the presence of two discrete Fe environments. The results suggested a lower degree of Ga clustering than has been previously observed in Fe–Ga alloys, of similar composition, prepared by melt spinning. The microstructure is similar to that of Fe–Ga thin films prepared by combinatorial sputtering. Some samples have also been studied after annealing at 800 °C for 8 h. No changes were observed in X-ray diffraction patterns after annealing. However, Mössbauer effect studies show the formation of D03 and L12 order in annealed samples analogous to the phases observed in melt spun ribbons of similar composition. 相似文献
5.
Mohammad Javad Nasr Isfahani Maxym Myndyk Jan Šubrt 《Journal of magnetism and magnetic materials》2010,322(13):1744-1747
The substituted nickel ferrite (NiFe2−2xSnxCuxO4, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe3+ ions by Sn4+ and Cu2+ cations on the structural and magnetic properties of the ferrite was studied by means of 57Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe2O4 adopts a fully inverse spinel structure of the type (Fe)[NiFe]O4, Sn4+ and Cu2+ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe1−2xSnxCux]O4, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe2−2xSnxCuxO4 samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement. 相似文献
6.
The roles of aliovalent CaII-for-YIII substitution and high-pressure-oxygen annealing in the process of ‘superconducterizing’ the Co-based layered copper oxide, CoSr2(Y1−xCax)Cu2O7+δ (Co-1212), were investigated. The as-air-synthesized samples up to x=0.4 were found essentially oxygen stoichiometric (−0.03≤δ≤0.00). These samples, however, were not superconducting, suggesting that the holes created by the divalent-for-trivalent cation substitution are trapped on Co in the charge reservoir. Ultra-high-pressure heat treatment carried out at 5 GPa and 500 °C for 30 min in the presence of Ag2O2 as an excess oxygen source induced bulk superconductivity in these samples. The highest Tc was obtained for the high-oxygen-pressure treated x=0.3 sample at ∼40 K. 相似文献
7.
O. MounkachiM. Hamedoun M. Belaiche A. Benyoussef R. MasrourH. El Moussaoui M. Sajieddine 《Physica B: Condensed Matter》2012,407(1):27-32
Polycrystalline Mg0.6Cu0.4Fe2O4 ferrites have been prepared using solid-state reaction technique. Their structural and magnetic properties have been studied, using X-ray diffraction and magnetic measurements.Using mean field theory and high-temperature series expansions (HTSE), extrapolated with the padé approximants method, the magnetic properties of Mg1−xCuxFe2O4 have been studied. The nearest neighbor super-exchange interactions for intra-site and inter-site of the Mg1−xCuxFe2O4 ferrites spinels, in the range 0≤x≤1, have been computed using the probability approach, based on Mössbauer data. The Curie temperature Tc is calculated as a function of Mg concentration. The obtained theoretical results are in good agreement with experimental ones obtained by magnetic measurements. 相似文献
8.
Arrays of Fe0.92−xCoxP0.08 (0.22≤x≤0.78) ternary alloy nanowires were fabricated in anodic aluminium oxide templates by electrochemical deposition. The broadened peaks in transmission Mössbauer spectra and the halo in selected area electron diffraction patterns indicate that the structure of Fe0.92−xCoxP0.08 nanowires is amorphous. However, the short-range order of Fe0.92−xCoxP0.08 nanowires has a bcc structure with a [110]-preferred orientation that is parallel to the nanowires. The magnetic texture results in the magnetic moment direction of the Fe atoms being along the nanowires. The short-range order around the Fe atoms reaches a minimum at x=0.45. With increasing Co content, the average hyperfine field decreases, while the isomer shift and quadrupole splitting remain almost constant, which result from the variation of 3d and 4s electron volume density at the Fe sites. 相似文献
9.
FexNi100−x thin films were produced by galvanostatic electrodeposition on Si (1 0 0), nominal thickness 2800 nm, and x ranging 7-20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature 57Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization. 相似文献
10.
11.
E.V. Tsipis V.V. Kharton E.N. Naumovich 《Journal of Physics and Chemistry of Solids》2006,67(8):1882-1887
The redox behavior of perovskite-type La0.90Sr0.10Al0.85−xFexMg0.15O3−δ (x=0.20-0.40) mixed conductors was analyzed by the Mössbauer spectroscopy and measurements of the total conductivity and Seebeck coefficient in the oxygen partial pressure range from 10−20 to 0.5 atm at 1023-1223 K. The results combined with oxygen-ion transference numbers determined by the faradaic efficiency technique in air, were used to calculate defect concentrations, mobilities, and partial ionic and p- and n-type electronic conductivities as a function of oxygen pressure. The redox and transport processes can be adequately described in terms of oxygen intercalation and iron disproportionation reactions, with the thermodynamic functions independent of defect concentrations. No essential delocalization of the electronic charge carriers was found. The oxygen non-stoichiometry values estimated from the conductivity vs. p(O2) dependencies, coincide with those evaluated from the Mössbauer spectra. 相似文献
12.
Xiangdong Meng Haibo Li Liu Mei Xiao Li 《Journal of magnetism and magnetic materials》2009,321(9):1155-1158
Mössbauer spectroscopy is used to characterize the crystallite size and structure of CoFe2−xYxO4 (x=0, 0.1, 0.3, 0.5) ferrite nanocrystallites synthesized by the sol-gel auto-combustion method. The effect of the substitution of Fe3+ ions by Y3+ ions on the structure of cobalt ferrite nanocrystallites is investigated. The Mössbauer spectra showed two sets of six-line hyperfine patterns for all the samples, indicating the presence of Fe in both A and B-sites. On increasing the concentration of doped Y, the hyperfine field strength and the isomer shift first increase and then decrease, whereas the quadrupole splitting continuously increases. The superparamagnetism was observed for all the samples and the change of ratio of the superparamagnetism component reflects the size of crystal grain. 相似文献
13.
Monica Sorescu Tianhong XuAdam Wise Marina Díaz-MichelenaMichael E. McHenry 《Journal of magnetism and magnetic materials》2012,324(7):1453-1462
The xFe2TiO4-(1−x)Fe3O4 pseudo-binary systems (0≤x≤1) of ulvöspinel component were synthesized by solid-state reaction between ulvöspinel Fe2TiO4 precursors and commercial Fe3O4 powders in stochiometric proportions. Crystalline structures were determined by X-ray powder diffraction (XRD) and it was found that the as-obtained titanomagnetites maintain an inverse spinel structure. The lattice parameter a of synthesized titanomagnetite increases linearly with the increase in the ulvöspinel component. 57Fe room temperature Mössbauer spectra were employed to evaluate the magnetic properties and cation distribution. The hyperfine magnetic field is observed to decrease with increasing Fe2TiO4 component. The fraction of Fe2+ in both tetrahedral and octahedral sites increases with the increase in Ti4+ content, due to the substitution and reduction of Fe3+ by Ti4+ that maintains the charge balance in the spinel structure. For x in the range of 0 ≤x≤0.4, the solid solution is ferrimagnetic at room temperature. However, it shows weak ferrimagnetic and paramagnetic behavior for x in the range of 0.4<x≤0.7. When x>0.70, it only shows paramagnetic behavior, with the appearance of quadrupole doublets in the Mössbauer spectra. Simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) studies showed that magnetite is not stable, and thermal decomposition of magnetite occurs with weight losses accompanying with exothermic processes under heat treatment in inert atmosphere. 相似文献
14.
M. Hamedoun A. Benyoussef M. Bousmina 《Journal of magnetism and magnetic materials》2010,322(21):3227-1638
Using mean field theory and high-temperature series expansions (HTSEs), extrapolated with the Padé approximants method, the effect of Zn doping on magnetic properties of NiFe2O4 ferrite spinel has been studied. The nearest neighbour super-exchange interactions for intra-site (JAA, JBB) and inter-site (JAB) of the ZnxNi1−xFe2O4 ferrites spinels, in the range 0≤x≤1, have been computed using the probability approach, based on Mössbauer data. The paramagnetic Curie-Weiss temperature θ and the Curie temperature TC are calculated as a function of Zn concentration. The critical exponent γ associated with magnetic susceptibility is calculated. The spin correlation functions intra-plane and inter-plane have been also computed and compared with exchange couplings. The obtained theoretical results are in good agreement with experimental ones obtained by magnetic measurements and Mössbauer spectroscopy. 相似文献
15.
Charge disproportionation in La0.5Ca0.5FeO3−δ perovskite has been detected by zero-field Mössbauer spectra from 20 K to room temperature. On the basis of the parameters of center shifts and hyperfine fields, Mössbauer spectra identified that the iron ionic states are Fe3+ and Fe5+ below 150 K, Fe3+, Fe4+ and Fe5+ in the intermediate temperature region, as well as Fe3+ and Fe4+ above 220 K. At low temperatures, the system exhibits a cluster-glass-like state resulting from competition between antiferromagnetic interaction of Fe3+–Fe3+ and ferromagnetic interaction of Fe3+–Fe5+. 相似文献
16.
Phonon dynamics was investigated on Y Mn1−xFexO3(0≤x≤0.20) hexagonal manganite polycrystals. Phonon modes were properly assigned using results obtained on Y MnO3 single crystal, by mixing the ab plane and the c axis optical responses. Upon increasing the Fe content, most of the phonon mode frequencies do not vary drastically. However, some modes involving Y and O atom displacements along the c axis are affected by doping. Indeed, a redshift of their transverse optical frequency was interpreted as an elongation of Y-O distance along the c-axis, resulting in a change in yttrium coordination. 相似文献
17.
T.P. Lu 《Journal of Physics and Chemistry of Solids》2011,72(5):442-444
The interplay between the superconducting phase and spin density wave order phase was studied. We report the magnetic and superconducting properties of the hole-doped FeAs-based superconducting compound La0.87−xLnxSr0.13FeAsO (Ln=Sm, Gd, Dy; 0≤x≤0.06). Both resistivity and magnetic susceptibility measurements show that the superconducting transition temperature decreases with increase in composition of magnetic ions. The hysteresis loop of the La0.87−xLnxSr0.13FeAsO sample shows a superconducting hysteresis in addition to a paramagnetic background. The experiment demonstrates that the magnetism and superconductivity coexist in hole-doped FeAs-based superconducting compounds. Among these three magnetic rare-earth elements, the influence of Dy3+ doping on superconductivity is more evident than that of Gd3+ doping, while the influence of Sm3+ doping is the weakest. The trend is consistent with the variation of the lattice parameter along c-axis. 相似文献
18.
The magnetic behavior of the FeInxCr2−xSe4 system (with x=0.0, 0.2 and 0.4) has been investigated by magnetic and Mössbauer spectroscopy. Hyperfine parameters indicate that iron is in the Fe2+ oxidation state, with a minor (∼9%) Fe3+ fraction, located at different layers in the structure. Low-field magnetization curves as a function of temperature showed that the antiferromagnetic (AFM) order temperature is TN=208(2) K for FeCr2Se4 and decreases to 174(3) K for FeIn0.4Cr1.6Se4. The effective magnetic moment μeff decreases with increasing In contents, and shows agreement with the expected values from the contribution of Fe2+ (5D) and Cr3+ (4F) electronic states. A second, low-temperature transition is observed at TG∼13 K, which has been assigned to the onset of a glassy state. 相似文献
19.
Jong Seong Bae Kyoo Sung Shim Soung-soo Yi Young Soo Kim 《Applied Surface Science》2006,252(13):4564-4568
The influence of lithium doping on the crystallization, the surface morphology, and the luminescent properties of pulsed laser deposited Y2−xGdxO3:Eu3+ thin film phosphors was investigated. The crystallinity, the surface morphology, and the photoluminescence (PL) of films depended highly on the Li-doping and the Gd content. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li+ doping was found to effectively enhance not only the crystallinity but also the luminescent brightness of Y2−xGdxO3:Eu3+ thin films. In particular, the incorporation of Li and Gd into the Y2O3 lattice could induce remarkable increase in the PL. The highest emission intensity was observed Li-doped Y1.35Gd0.6O3:Eu3+ thin films whose brightness was increased by a factor of 4.6 in comparison with that of Li-doped Y2O3:Eu3+ thin films. 相似文献
20.
Spectral studies of Co substituted Ni-Zn ferrites 总被引:1,自引:0,他引:1
M.A. Amer A. TawfikA.G. Mostafa A.F. El-ShoraS.M. Zaki 《Journal of magnetism and magnetic materials》2011,323(11):1445-1452
The spinel ferrites Zn0.35Ni0.65−xCoxFe2O4, 0≤x≤1, have been prepared using the standard ceramic technique. Room temperature Mössbauer, X-ray and infrared IR spectra were used for carrying out this study. X-ray patterns reveal that all the samples have single-phase cubic spinel structure. The Mössbauer spectra of the samples show a paramagnetic phase for x=0 and a six-line magnetic pattern and a central paramagnetic phase for x≥0.1. They are analyzed and attributed to two magnetic subpatterns and two quadrupole doublets due to Fe3+ ions at the tetrahedral A-sites and octahedral B-sites. Four absorption bands are observed in IR spectra. They confirm the spinel structure of the samples and existence of Fe3+ ions in the sample sublattices. The deduced hyperfine interactions, lattice parameters, absorption band positions and intensities and force constant are found to be dependent on the substitution factor x, where the cation distribution is estimated. The hyperfine magnetic fields, magnetization and lattice resonant frequency are found to be dependent on the interionic distance. 相似文献