共查询到20条相似文献,搜索用时 31 毫秒
1.
M.J. Martínez-Lope M. García-Hernández J.A. Alonso 《Journal of solid state chemistry》2009,182(3):532-537
The title compound has been first synthesized by a citrate technique followed by thermal treatments under moderate oxygen pressure conditions, and characterized by X-ray and neutron powder diffraction (NPD) and magnetization measurements. The crystal structure of DyCrMnO5 has been refined from NPD data in the space group Pbam; a=7.2617(6) Å, b=8.5161(6) Å, and c=5.7126(5) Å at 295 K. This oxide is isostructural with RMn2O5 oxides (R=rare earths) and it contains infinite chains of (Cr, Mn)4+O6 octahedra-sharing edges, linked together by (Mn, Cr)3+O5 pyramids and DyO8 units. The high degree of antisite disordering exhibited by DyCrMnO5 is noteworthy. The octahedral positions are occupied by roughly 50% of Mn and Cr cations, and the pyramidal groups contain two thirds of Mn and one third of Cr cations. We assume that Mn and Cr cations at the octahedral positions exhibit a tetravalent oxidation state, whereas the metals at the pyramidal positions are trivalent, in order to preserve the electroneutrality of this oxide. The susceptibility vs temperature curve of DyCrMnO5 does not suggest the establishment of a long-range magnetic structure even at low temperatures; the NPD technique does not provide any signal of magnetic ordering, since the reflections do not show any magnetic contribution. 相似文献
2.
M. Retuerto M.J. Martínez-Lope M.T. Fernández-Díaz 《Journal of solid state chemistry》2011,184(9):2428-2433
The title compounds have been synthesized by a citrate technique followed by thermal treatments in air (BiFe0.5Mn1.5O5) or under high oxygen pressure conditions (BiFeMnO5), and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization measurements. The crystal structures have been refined from NPD data in the space group Pbam at 295 K. These phases are isostructural with RMn2O5 oxides (R=rare earths) and contain infinite chains of Mn4+O6 octahedra sharing edges, linked together by (Fe,Mn)3+O5 pyramids and BiO8 units. These units are strongly distorted with respect to those observed in other RFeMnO5 compounds, due to the presence of the electronic lone pair on Bi3+. It is noteworthy the certain level of antisite disorder exhibited in both samples, where the octahedral positions are partially occupied by Fe cations, and vice versa. BiFexMn2−xO5 (x=0.5, 1.0) are short-range magnetically ordered below 20 K for x=0.5 and at 40 K for x=1.0. The main magnetic interactions seem to be antiferromagnetic (AFM); however, the presence of a small hysteresis in the magnetization cycles indicates the presence of some weak ferromagnetic (FM) interactions. 相似文献
3.
The structure, the energetics and the internal redox reactions of La0.7Sr0.3FexMn1−xO3 have been studied in the complete solid solution range 0.0<x<1.0. High temperature oxide melt drop solution calorimetry was performed to determine the enthalpies of formation from binary oxides and the enthalpy of mixing. There is a noticeable change in the energetics of the solid solution near x=0.7, which is due to the growing concentration of Fe4+ at higher Fe/(Fe+Mn) ratio. The balance between different valences of the transition metals, Mn and Fe, is the main factor in determining the energetics of the La0.70Sr0.30FexMn1−xO3 solid solution. 相似文献
4.
Farshid Ramezanipour Bradley Cowie Shahab Derakhshan John E. Greedan Lachlan M.D. Cranswick 《Journal of solid state chemistry》2009,182(1):153-3227
The crystal and magnetic structures of the brownmillerite material, Ca2Fe1.039(8)Mn0.962(8)O5 were investigated using powder X-ray and neutron diffraction methods, the latter from 3.8 to 700 K. The compound crystallizes in Pnma space group with unit cell parameters of a=5.3055(5) Å, b=15.322(2) Å, c=5.4587(6) Å at 300 K. The neutron diffraction study revealed the occupancies of Fe3+ and Mn3+ ions in both octahedral and tetrahedral sites and showed some intersite mixing and a small, ∼4%, Fe excess. While bulk magnetization data were inconclusive, variable temperature neutron diffraction measurements showed the magnetic transition temperature to be 407(2) K below which a long range antiferromagnetic ordering of spins occurs with ordering wave vector k=(000). The spins of each ion are coupled antiferromagnetically with the nearest neighbors within the same layer and coupled antiparallel to the closest ions from the neighboring layer. This combination of intra- and inter-layer antiparallel arrangement of spins forms a G-type magnetic structure. The ordered moments on the octahedral and tetrahedral sites at 3.8 K are 3.64(16) and 4.23(16) μB, respectively. 相似文献
5.
H. El Shinawi 《Journal of solid state chemistry》2008,181(10):2705-2712
The K2NiF4 phases LaSrCo0.5Fe0.5O4 and La1.2Sr0.8Co0.5Fe0.5O4, and their reduced forms LaSrCo0.5Fe0.5O3.75 and La1.2Sr0.8Co0.5Fe0.5O3.85, have been successfully prepared by solid-state reactions, followed by reduction in 10% H2/N2 in order to produce oxygen-deficient materials. All materials crystallize in a tetragonal K2NiF4 structure (space group I4/mmm) with Co and Fe randomly distributed over the B-sites of the structure. Mössbauer spectra have confirmed the trivalent state of Fe in these materials. In the reduced materials, oxide ion vacancies are confined to the equatorial planes of the K2NiF4 structure and the Co is present almost entirely as Co2+ ions; low-temperature neutron powder diffraction data reveal that these reduced phases are antiferromagnetically ordered with a tetragonal noncollinear arrangement of the moments. The Co3+ ions, present in stoichiometric LaSrCo0.5Fe0.5O4 and La1.2Sr0.8Co0.5Fe0.5O4, inhibit magnetic order and are assumed to be in the low-spin state. 相似文献
6.
Frank J. Berry Fiona C. Coomer Örn Helgason Peter R. Slater Michael F. Thomas 《Journal of solid state chemistry》2011,184(6):1361-1366
Fluorination of the parent oxide, BaFeO3−δ, with polyvinylidine fluoride gives rise to a cubic compound with a=4.0603(4) Å at 298 K. 57Fe Mössbauer spectra confirmed that all the iron is present as Fe3+. Neutron diffraction data showed complete occupancy of the anion sites, indicating a composition BaFeO2F, with a large displacement of the iron off-site. The magnetic ordering temperature was determined as TN=645±5 K. Neutron diffraction data at 4.2 K established G-type antiferromagnetism with a magnetic moment per Fe3+ ion of 3.95 μB. However, magnetisation measurements indicated the presence of a weak ferromagnetic moment that is assigned to the canting of the antiferromagnetic structure. 57Fe Mössbauer spectra in the temperature range 10-300 K were fitted with a model of fluoride ion distribution that retains charge neutrality of the perovskite unit cell. 相似文献
7.
Ian D. Fawcett Gabriel M. Veith Martha Greenblatt Mark Croft Israel Nowik 《Solid State Sciences》2000,2(8)
The SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe3+ and Fe4+. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn4+, Fe(4+δ)+ and Fe(3+)+. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-eg orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe(3+)+/Fe(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution. 相似文献
8.
Igor Presniakov Alexei Baranov Alexei Sobolev Viyacheslav Rusakov 《Journal of solid state chemistry》2007,180(11):3253-3261
For the first time a comparative study of rhombohedral LaNiO3 and LaCuO3 oxides, using 57Fe Mössbauer probe spectroscopy (1% atomic rate), has been carried out. In spite of the fact that both oxides are characterized by similar crystal structure and metallic properties, the behavior of 57Fe probe atoms in such lattices appears essentially different. In the case of LaNi0.99Fe0.01O3, the observed isomer shift (δ) value corresponds to Fe3+ (3d5) cations in high-spin state located in an oxygen octahedral surrounding. In contrast, for the LaCu0.99Fe0.01O3, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe4+(3d4) cations in octahedral coordination within Fe(IV) perovskite-like ferrates. To explain such a difference, an approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that in the case of LaNi0.99Fe0.01O3, electronic state of nickel is dominated by the d7 configuration corresponding to the formal ionic “Ni3+-O2−” state. On the other hand, in the case of LaCu0.99Fe0.01O3 a large amount of charge is transferred via Cu-O bonds from the O:2p bands to the Cu:3d orbitals and the ground state is dominated by the d9L configuration (“Cu2+−O” state). The dominant d9L ground state for the (CuO6) sublattice induces in the environment of the 57Fe probe cations a charge transfer Fe3++O−(L)→Fe4++O2−, which transforms “Fe3+” into “Fe4+” state. The analysis of the isomer shift value for the formally “Fe4+” ions in perovskite-like oxides clearly proved a drastic influence of the 4s iron orbitals population on the Fe−O bonds character. 相似文献
9.
Nasr-Allah M Deraz 《Thermochimica Acta》2003,401(2):175-185
Mn/Fe mixed oxide solids doped with Al2O3 (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area (SBET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N2 adsorption isotherms and CO oxidation by O2. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn2O3 interacted readily with Fe2O3 to produce well-crystallized manganese ferrite (MnFe2O4) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al2O3-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al2O3 followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and SBET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al2O3 added, due to the enhanced formation of MnFe2O4 phase which is less reactive than the free oxides (Mn2O3 and Fe2O3). The activation energy of formation (ΔE) of MnFe2O4 was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe2O4 was attributed to an effective increase in the mobility of reacting cations. 相似文献
10.
Artem M Abakumov Marina G Rozova Evgeny V Antipov Gustaaf Van Tendeloo 《Journal of solid state chemistry》2004,177(8):2855-2861
The new Pb5Sb2MnO11 compound was synthesized using a solid-state reaction in an evacuated sealed silica tube at 650°C. The crystal structure was determined ab initio using a combination of X-ray powder diffraction, electron diffraction and high-resolution electron microscopy (a=9.0660(8)Å, b=11.489(1)Å, c=10.9426(9)Å, S.G. Cmcm, RI=0.045, RP=0.059). The Pb5Sb2MnO11 crystal structure represents a new structure type and it can be considered as quasi-one-dimensional, built up of chains running along the c-axis and consisting of alternating Mn+2O7 capped trigonal prisms and Sb2O10 pairs of edge sharing Sb+5O6 octahedra. The chains are joined together by Pb atoms located between the chains. The Pb+2 cations have virtually identical coordination environments with a clear influence of the lone electron pair occupying one vertex of the PbO5E octahedra. Electronic structure calculations and electron localization function distribution analysis were performed to define the nature of the structural peculiarities. Pb5Sb2MnO11 exhibits paramagnetic behavior down to T=5 K with Weiss constant being nearly equal to zero that implies lack of cooperative magnetic interactions. 相似文献
11.
The vanadium oxide bronzes θ-(Fe1?yAly)xV2O5 are Curie-Weiss paramagnets and hopping semiconductors. The samples studied were synthesized by direct solid-state reaction and investigated by the X-ray diffraction, differential thermal analysis, electrical resistivity, magnetic susceptibility, and Mössbauer techniques. The crystal lattice parameters, effective magnetic moments of Fe3+ cations, Curie-Weiss temperatures, and the values of 57Fe hyperfine interaction parameters were determined. Endothermic effects were observed for some of the samples. 相似文献
12.
《Solid State Sciences》2000,2(5):539-544
The crystal structure of Ba11Fe8Ti9O41 was determined using single crystal and powder X-ray diffraction methods. This new phase crystallizes in the hexagonal space group P63/mmc (No 194) (a=5.7506(3) Å, c=61.413(2) Å; Z=2; ρcalc.=5.75 g cm−3) and exhibits a 26-layer structure built from close-packed [O,(Ba,O)] layers with a stacking sequence (chcchchchcchc)2. Octahedral sites are occupied by a mixture of Fe3+ and Ti4+, with some preferential ordering of the Fe ions, and tetrahedral sites are occupied by Fe3+. The magnetic Fe ions were observed to concentrate within four contiguous cp layers around z=1/4 and 3/4. Unusual structural features, including cation disorder associated with unreasonably short cation–cation separations, were observed to occur within these magnetic sections of the structure. Indexed X-ray powder diffraction data for polycrystalline Ba11Fe8Ti9O41 are given. Complementary structural studies of this compound using neutron and electron diffraction are underway and will be described elsewhere along with the results of dielectric and magnetic property measurements. 相似文献
13.
Mössbauer spectroscopy of layered YBaCo3.96Fe0.04O7+δ (δ=0.02 and 0.80), where 1% cobalt is substituted with 57Fe isotope, revealed no evidence of charge ordering at 4-293 K. The predominant state of iron cations was found trivalent, irrespective of their coordination and oxygen stoichiometry variations determined by thermogravimetric analysis. The extremely slow kinetics of isothermal oxidation at 598 K in air, and the changes of Fe3+ fractions in the alternating triangular and Kagomé layers in oxidized YBaCo3.96Fe0.04O7.80, may suggest that oxygen intercalation is accompanied with a substantial structural reconstruction stagnated due to sluggish cation diffusion. Decreasing temperature below 75-80 K leads to gradual freezing of the iron magnetic moments in inverse correlation with the content of extra oxygen. The formation of metal-oxygen octahedra and resultant structural distortions extend the temperature range where the paramagnetic and frozen states co-exist, down to 45-50 K. 相似文献
14.
Yasuhiko Takahashi Ken-ichi Ohshima Junji Awaka Junji Akimoto 《Journal of solid state chemistry》2007,180(3):1020-1027
Single crystals of calcium ferrite CaFe2O4-type NaTi2O4 having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO2 in a sealed iron vessel at 1473 K. Sodium-deficient NaxTi2O4 single crystals with 0.558<x<1 were successfully synthesized by a topotactic oxidation reaction using NaTi2O4 single crystals as parent materials. The crystal structures of NaxTi2O4 with x=0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the Ti1O6 and Ti2O6 double rutile chains was maintained in these NaxTi2O4 compounds. Based on the results of bond valence analysis, we speculated that the Ti1 sites are preferentially occupied by Ti3+ cations over the compositional range of 0.8<x<1, while both the Ti1 and Ti2 sites are randomly occupied by Ti3+ and Ti4+ cations at x=0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi2O4 is suppressed by an Na deficiency and vanishes in Na0.717Ti2O4. The electrical resistivity increased with the Na deficiency; however, it was still semiconductive in Na0.799Ti2O4. 相似文献
15.
The crystal structures and magnetic properties of the quaternary lanthanide oxides Ba6Ln2Fe4O15 (Ln=Pr and Nd) are reported. They crystallize in a hexagonal structure with space group P63mc and have the “Fe4O15 cluster” consisting of one FeO6 octahedron and three FeO4 tetrahedra. Measurements of the magnetic susceptibility, specific heat, and powder neutron diffraction reveal that this cluster behaves as a spin tetramer with a ferrimagnetic ground state of ST=5 even at room temperature. The cluster moments show a long-range antiferromagnetic ordering at 23.2 K (Ln=Pr) and 17.8 K (Nd), and the magnetic moments of the Ln3+ ions also order cooperatively. By applying the magnetic field (∼2 T), this antiferromagnetic ordering of the clusters changes to a ferromagnetic one. This result indicates that there exists a competition in the magnetic interaction between the clusters. 相似文献
16.
Michael W. Lufaso Terrell A. Vanderah Ileana M. Pazos Robert S. Roth Virgil Provenzano 《Journal of solid state chemistry》2006,179(12):3900-3910
Subsolidus phase relations have been determined for the Bi2O3-Fe2O3-Nb2O5 system in air (900-1075 °C). Three new ternary phases were observed—Bi3Fe0.5Nb1.5O9 with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi17Fe2Nb31O106 and Bi17Fe3Nb30O105 that appear to be structurally related to Bi8Nb18O57. The fourth ternary phase found in this system is pyrochlore (A2B2O6O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi2FeNbO7) suggesting that ≈4-15% of the A-sites are occupied by Fe3+. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi2O3:Fe2O3:Nb2O5 using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi1.721Fe0.190(Fe0.866Nb1.134)O7, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi1.5Zn0.92Nb1.5O6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi1.657Fe1.092Nb1.150O7 exhibited low-temperature dielectric relaxation similar to that observed for Bi1.5Zn0.92Nb1.5O6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed. 相似文献
17.
C.A. López J.C. Pedregosa R.E. Carbonio M.T. Fernández-Díaz 《Journal of solid state chemistry》2008,181(11):3095-3102
La-doped Sr2CoWO6 double perovskites have been prepared in air in polycrystalline form by solid-state reaction. These materials have been studied by X-ray powder diffraction (XRPD), neutron powder diffraction (NPD) and magnetic susceptibility. The structural refinement was performed from combined XRPD and NPD data (D2B instrument, λ=1.594 Å). At room temperature, the replacement of Sr2+ by La3+ induces a change of the tetragonal structure, space group I4/m of the undoped Sr2CoWO6 into the distorted monoclinic crystal structure, space group P21/n, Z=2. The structure of La-doped phases contains alternating CoO6 and (Co/W)O6 octahedra, almost fully ordered. On the other hand, the replacement of Sr2+ by La3+ induces a partial replacement of W6+ by Co2+ into the B sites, i.e. Sr2−xLaxCoW1−yCoyO6 (y=x/4) with segregation of SrWO4. Magnetic and neutron diffraction measurements indicate an antiferromagnetic ordering below TN=24 K independently of the La-substitution. 相似文献
18.
19.
用改进的Hummers法制备了氧化石墨烯,用乙二胺、乙二胺与丁二胺/己二胺混溶来改性氧化石墨烯。用水热法制备了Fe3O4,并用物理混合法制备了GO/Fe3O4/有机胺的三元复合体系。用透射电镜、扫描电镜、红外光谱、热重分析、X射线衍射、VSM和XPS等对所制得的样品进行了结构表征和性能测试,研究了三元复合粒子对结晶紫染料的吸附性能及影响结晶紫染料吸附效果的因素。结果表明:所制备的Fe3O4的平均粒径约为200 nm,粒径分布均匀;复合物中GO为典型的片状结构,GO及有机胺的掺杂没有影响Fe3O4的尖晶石结构;复合物为超顺磁性,Ms为53.0 emu·g~(-1)。吸附结果表明:石墨烯/Fe3O4/有机胺的三元复合材料对结晶紫染料的最大吸附量随浓度增大而增大,而吸附结晶紫染料的移除率却随结晶紫染料浓度增大而减小,并趋向一定值;乙二胺和己二胺混溶比例为5∶1的GO/Fe3O4复合材料吸附性能最佳:结晶紫浓度为400 mg·L~(-1),最大吸附量为164.3 mg·L~(-1)。 相似文献
20.
以有机碱四甲基氢氧化铵(TMAH)为沉淀剂合成了纳米Fe3O4和Co2+掺杂的纳米Fe3O4粒子。分别讨论了碱用量,铁盐溶液浓度,反应温度,有机碱及PEG-4000的分散性等因素对纳米Fe3O4的形貌影响。结果表明,所合成的纳米Fe3O4为30nm左右的反尖晶石型面心立方结构,有机碱除了起沉淀剂作用,还能够提高纳米Fe3O4的分散性。本文还讨论了不同Co2+掺入量的纳米Fe3O4粒子的磁性质,结果表明Co2+掺杂的纳米Fe3O4粒子的矫顽力在不同掺入量的下有较大的改变。当Co2+掺入量为10.0%时,纳米Fe3O4的矫顽力达到最大值,为1628Oe。 相似文献