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1.
M. Zhang  G.Z. Zhu 《Materials Letters》2008,62(28):4374-4376
This paper reports a preliminary study of Mn5Si3 precipitates in an Mg-Sn-Mn-Si alloy. The transmission electron microscopy investigation reveals that the Mn5Si3 precipitates have a plate shape, approximately 50 nm in thickness and 200 nm in width. The orientation relationship (OR) between the precipitates and matrix is not unique, but all measured ORs obey the following relationship: g(1 0 − 1 0)Mn5Si3 // Δg1 // Δg2, where Δg1 = g(2 − 1 − 1 0)Mn5Si3 − g(0 0 0 2)Mg, Δg2 = g(3 − 1 − 2 0)Mn5Si3 − g(0 0 0 2)Mg. The precipitate morphology and their OR with the matrix are explained with a Δg parallelism rule, showing good agreement.  相似文献   

2.
The (C3H12N2)0.94[Mn1.50Fe1.50III(AsO4)F6] and (C3H12N2)0.75[Co1.50Fe1.50III(AsO4)F6] compounds 1 and 2 have been synthesized using mild hydrothermal conditions. These phases are isostructural with (C3H12N2)0.75[Fe1.5IIFe1.5III(AsO4)F6]. The compounds crystallize in the orthorhombic Imam space group. The unit cell parameters calculated by using the patterns matching routine of the FULPROOF program, starting from the cell parameters of the iron(II),(III) phase, are: a = 7.727(1) Å, b = 11.047(1) Å, c = 13.412(1) Å for 1 and a = 7.560(1) Å, b = 11.012(1) Å, c = 13.206(1) Å for 2, being Z = 8 in both compounds. The crystal structure consists of a three-dimensional framework constructed from edge-sharing [MII(1)2O2F8] (M = Mn, Co) dimeric octahedra linked to [FeIII(2)O2F4] octahedra through the F(1) anions and to the [AsO4] tetrahedra by the O(1) vertex. This network gives rise two kinds of chains, which are extended in perpendicular directions. Chain 1 is extended along the a-axis and chain 2 runs along the c-axis. These chains are linked by the F(1) and O(1) atoms and establish cavities delimited by eight or six polyhedra along the [1 0 0] and [0 0 1] directions, respectively. The propanediammonium cations are located inside these cavities. The thermal study indicates that the structures collapse with the calcination of the organic dication at 255 and 285 °C for 1 and 2, respectively. The Mössbauer spectra in the paramagnetic state indicate the existence of two crystallographically independent positions for the iron(III) cations and a small proportion of this cation in the positions of the divalent Mn(II) and Co(II) ones. The IR spectrum shows the protonated bands of the H2N- groups of the propanediamine molecule and the characteristic bands of the [AsO4]3− arsenate oxoanions. In the diffuse reflectance spectra, it can be observed the bands characteristic of trivalent iron(III) cation and divalent Mn(II) and Co(II) ones in a distorted octahedral symmetry. The calculated Dq and B-Racah parameters for the cobalt(II) phase are 710 and 925 cm−1, respectively. The ESR spectra of compound 1 maintain isotropic with variation in temperature, being g = 1.99. Magnetic measurements for both compounds indicate that the main magnetic interactions are antiferromagnetic in nature. However, at low temperatures small ferromagnetic components are detected, which are probably due to a spin decompensation of the two different metallic cations. The hysteresis loops give values of the remnant magnetization and coercive field of 84.5, 255 emu/mol and 0.01, 0.225 T for phases 1 and 2, respectively.  相似文献   

3.
A new lithium iron(III) phosphate, Li9Fe7(PO4)10, has been synthesized and is currently under electrochemical evaluation as an anode material for rechargeable lithium-ion battery applications. The sample was prepared via the ion exchange reaction of Cs5K4Fe7(PO4)101 in the 1 M LiNO3 solution under hydrothermal conditions at 200 °C. The fully Li+-exchanged sample Li9Fe7(PO4)102 cannot yet be synthesized by conventional high-temperature, solid-state methods. The parent compound 1 is a member of the Cs9−xKxFe7(PO4)10 series that was previously isolated from a high-temperature (750 °C) reaction employing the eutectic CsCl/KCl molten salt. The polycrystalline solid 1 was first prepared in a stoichiometric reaction via conventional solid-state method then followed by ion exchange giving rise to 2. Both compounds adopt three-dimensional structures that consist of orthogonally interconnected channels where electropositive ions reside. It has been demonstrated that the Cs9−xKxFe7(PO4)10 series possesses versatile ion exchange capabilities with all the monovalent alkali metal and silver cations due to its facile pathways for ion transport. 1 and 2 were subject to electrochemical analysis and preliminary results suggest that the latter can be considered as an anode material. Electrochemical results indicate that Li9Fe7(PO4)10 is reduced below 1 V (vs. Li) to most likely form a Fe(0)/Li3PO4 composite material, which can subsequently be cycled reversibly at relatively low potential. An initial capacity of 250 mAh/g was measured, which is equivalent to the insertion of thirteen Li atoms per Li9+xFe7(PO4)10 (x = 13) during the charge/discharge process (Fe2+ + 2e → Fe0). Furthermore, 2 shows a lower reduction potential (0.9 V), by approximately 200 mV, and much better electrochemical reversibility than iron(III) phosphate, FePO4, highlighting the value of improving the ionic conductivity of the sample.  相似文献   

4.
Parameterization of the electronic band structure of CuIn1−xGaxSe2 (x = 0, 0.5, and 1) demonstrates that the energy dispersions of the three uppermost valence bands [Ej(k); j = v1, v2, and v3] are strongly anisotropic and non-parabolic even very close to the Γ-point valence-band maximum Ev1(0). Also the lowest conduction band Ec1(k) is anisotropic and non-parabolic for energies ~ 0.05 eV above the band-gap energy. Since the electrical conductivity depends directly on the energy dispersion, future electron and hole transport simulations of CuIn1−xGaxSe2 need to go beyond the parabolic approximation of the bands. We therefore present a parameterization of the energy bands, the k-dependency of the effective electron and hole masses mj(k), and also an average energy-dependent approximation of the masses mj(E).  相似文献   

5.
Uniform Fe3O4 nanoparticles with diameters of 3-5 nm are successfully decorated onto the external walls of multiwall carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of Fe(acac)3 in polyol solution under the irradiation of microwave. With this method, reaction time of forming Fe3O4-MWCNTs nanocomposites has been significantly shortened to 15 min. The resulting Fe3O4-MWCNTs nanocomposites show superparamagnetic property at room temperature and can be remained as stable aqueous dispersion for 2 months. Longitudinal relaxivity (r1) and transverse relaxivity (r2) of the magnetic MWCNTs are 8.34 Fe mM−1 S−1 and 146 Fe mM−1 S−1 respectively. The much higher r2 value and the obvious change in the gray scale of MR images confer the Fe3O4-MWCNTs nanocomposites as potential candidates for T2-weighted MRI contrast agents.  相似文献   

6.
7.
Preparation of magnesium aluminate spinel powder by hydrothermal-assisted sol-gel processing from MgAl2(OCH2CH2OR)8, RCH3 (1), CH2CH2OCH3 (2), MgAl2[OCH(CH3)2]8 (3) and MgAl2(O-sBu)8 (4) in toluene and parent alcohol has been investigated. Coordination status of aluminum atom in precursors was determined by 27Al NMR and correlation between coordination number of aluminum and development of spinel phase in hydrothermal-assisted sol-gel processing has been studied. The gels obtained from hydrothermal-assisted hydrolysis of magnesium-aluminum alkoxides that contain six-coordinated aluminum atoms in solution (1 and 2) after calcination at 700 °C resulted in the formation of pure spinel phase, whereas in similar hydrolysis and calcination processes of precursors that contain four-coordinated aluminum (3 and 4) spinel phase forms along with some Al2O3 and MgO. Selected powders obtained from hydrothermal-assisted sol-gel processing were characterized by thermal analysis (TGA/DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Results indicate that the coordination status of aluminum in the precursor is very crucial for the formation of pure phase spinel. The morphology of prepared spinels was studied by SEM and the results showed that the solvent in hydrothermal-assisted sol-gel processing has a marked effect on the morphology of the resulting MgAl2O4. In hydrothermal-assisted sol-gel processing of aluminum-magnesium alkoxides in hydrophobic solvent, spherical particles are formed, while in the parent alcohol, non-spherical powders are formed.  相似文献   

8.
0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3(PNN-PZT) ceramics with different concentration of xFe2O3 doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe2O3. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d33 ~ 956 pC/N, the electromechanical coupling factor kp ~ 0.74, and the dielectric constant εr ~ 6095 are achieved for the specimen with 1.2 mol% Fe2O3 doping sintered at 1200 °C for 2 h.  相似文献   

9.
Li3 − xFe2 − xTix(PO4)3/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li3Fe2(PO4)3/C (x = 0) and Li2.8Fe1.8Ti0.2(PO4)3/C (x = 0.2) possess two plateau potentials of Fe3+/Fe2+ couple (around 2.8 V and 2.7 V vs. Li+/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li2.8Fe1.8Ti0.2(PO4)3/C has higher reversibility and better capacity retention than that of the undoped Li3Fe2(PO4)3/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.  相似文献   

10.
The [N(CH3)4][N(C2H5)4]ZnCl4 compound was prepared and characterized by electrical technique. The temperature dependence of the dielectric permittivity shows that this compound is ferroelectric below T = 268 K. The two semi-circles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in the material. The equivalent circuit is modeled by a combination series of two parallel RP–CPE circuits. The frequency dependent conductivity is interpreted in term of Jonscher's law. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (K.W.W.) function: ?(t) = exp [(−t/τ)β]. The temperature dependence of the alternative current conductivity (σp), direct current conductivity (σdc) and the relaxation frequency (fp) confirm the presence of the ferroelectric–paraelectric phase transition.  相似文献   

11.
A new iron phosphonate-oxalate [Fe(O3PCH3)(C2O4)0.5(H2O)] (1), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction studies reveal that 1 consists of layers of vertex-linked FeO6 octahedra and O3PC tetrahedra, which are further connected by bis-chelate oxalate bridges, giving to a 3D structure with 10-membered channels. Crystal data: monoclinic, P21/n (no. 14), a = 4.851(2) Å, b = 16.803(7) Å, c = 7.941(4) Å, β = 107.516(6)°, V = 617.2(5) Å3, Z = 4, R1 = 0.0337 and wR2=0.0874 for 1251 reflections [I > 2σ(I)]. Mössbauer spectroscopy measurement confirms the existence of high-spin Fe(III) in 1. Magnetic studies show that 1 exhibits weak ferromagnetism with TN = 30 K due to a weak spin canting.  相似文献   

12.
We describe transformations of the Dion-Jacobson (D-J) phases, KLaNb2O7 and RbBiNb2O7, to the Aurivillius (A) phases, (PbBiO2)LaNb2O7 (1) and (PbBiO2)BiNb2O7 (2), in a metathesis reaction with PbBiO2Cl. Oxide 1 adopts centrosymmetric tetragonal structure (a = 3.905(1) Å, c = 25.66(1) Å), whereas oxide 2 crystallizes in a noncentrosymmetric orthorhombic (A21am) (a = 5.489(1) Å, b = 5.496(2) Å, c = 25.53(1) Å) structure. Oxide 2 shows a distinct SHG response towards 1064 nm laser radiation. The role of La3+ versus Bi3+ in the perovskite slabs for the occurrence of noncentrosymmetric structure/ferroic property in these materials is pointed out.  相似文献   

13.
We study the structural stability of surfactant coated ZnFe2O4 (ZF) nanoparticles of average particle size 10 nm annealed under different environments. The X-ray diffraction studies in oleic acid coated ZF (OC-ZF) show distinctly different phase transitions under different annealing conditions. The OC-ZF is reduced to α-Fe/ZnO phase under vacuum while it forms FeO/ZnO under argon whereas the ZnFe2O4 phase remains stable under air annealing. The simultaneous thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) coupled mass spectra (MS) in OC-ZF under argon atmosphere suggests that the residual carbon removes oxygen from the lattice to reduce the ZnFe2O4 phase into FeO/ZnO during argon annealing. Apart from CO and CO2 gas evolution at high temperature under argon annealing, creation of oxygen vacancies due to the random removal of oxygen under vacuum annealing, leads to direct interaction between Fe–Fe and the formation of metal Fe. It appears that the residual carbon aids the reduction of ZF and the formation of α-Fe/ZnO during vacuum annealing. After annealing at 1000 °C in vacuum, the magnetization is increased abruptly from 13.8 to 106.5 emu g−1. In sharp contrast, the air and argon annealed samples show a diminished magnetization of 1 emu g−1. The field cooled (FC) and zero FC magnetization of vacuum and argon annealed samples exhibit superparamagnetic and spin-glass type behavior respectively. Our results offer possibilities to switch a magnetically inactive material to an active one.  相似文献   

14.
An easy route is described for the synthesis of monodisperse oleic acid-coated Fe3O4 nanoparticles with uniform size and shape via a thermal decomposition of Fe(acac)3 in the presence of oleic acid (OA). The prepared Fe3O4 samples are characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectrometry, and vibrating sample magnetometer. The results show that the resulting OA-coated Fe3O4 nanoparticles have an average diameter of about 24 nm and an OA layer, around 3 nm in thickness. The magnetic saturation value of the prepared OA-coated Fe3O4 nanoparticles is determined to be 78.68 emu/g, indicating a well-established superparamagnetic property.  相似文献   

15.
16.
SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposite ferrite microfibers with diameters of 1–2 μm have been prepared by the sol–gel process. The SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposite ferrites are formed after the precursor calcined at 850 °C for 2 h, fabricating from nanosized particles with a uniform phase distribution. The ferrite grain size increases with the calcination temperature. The magnetic properties for the nanocomposite ferrite microfibers are mainly influenced by the chemical composition and grain size. The nanocomposite ferrite microfibers obtained at 900 °C show the enhanced specific saturation magnetization (Msh) of 64.8 Am2 kg−1, coercivity (Hc) of 146.5 kA m−1 and remanence (Mr) of 33.6 Am2 kg−1 owing to the exchange–coupling interaction. This exchange–coupling interaction in the SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposite ferrite microfibers has been discussed.  相似文献   

17.
Fe3BO6 can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe3BO6 growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B2O3 − xFe2O3, x = 40–50 mol%. B2O3 as a strong glass former co-bridges the Fe3+ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe3+ species in form of a compound Fe3BO6, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B2O3 layer (15–25 nm thickness) has grown on the Fe3BO6 of the nanorods in situ in a specific structure. XPS bands in the Fe3+, B3+ and O2− species confer this model structure. A local BO3 → BO4 conversion has incurred in the boroxol (B3O4.5)n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm−1.  相似文献   

18.
Fe-phthalocyanine/Fe3O4 hybrid microspheres were synthesized from bis-phthalonitrile and FeCl3·6H2O through a simple and effective solvent-thermal route. The hybrids were monodispersed solid microspheres with diameter of ~ 400 nm. The ferromagnetic signature emerged with the saturated magnetization of ~ 55.7 emu g−1, and the coercive force of ~ 93.7 Oe at 300 k. The addition of bis-phthalonitrile oligomer brought Fe3O4 nanoparticles novel dielectric property: a new dielectric loss peak appeared at ~ 8 GHz. Considering the microwave magnetic loss properties, two microwave magnetic loss peaks were presented at ~ 1.5 GHz and ~ 10 GHz, the former peak was attributed to the natural properties of the Fe3O4, and the latter originated from the interface effects between the bis-phthalonitrile oligomer and Fe3O4.  相似文献   

19.
A novel approach, combining in-situ composite method with electrospinning, was used to prepare high magnetic Fe3O4/poly(vinyl alcohol) (PVA) composite nanofibers. Fe3O4 magnetic fluids were synthesized by chemical co-precipitation method in the presence of 6 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resulting Fe3O4/PVA composite nanofibers were characterized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD), respectively. These composite fibers showed a uniform and continuous morphology, with the Fe3O4 nanoparticles embedded in the fibers. Magnetization test confirmed that the composite fiber showed a high saturated magnetization (Ms = 2.42 emµ·g-1) although only 4 wt.% content.  相似文献   

20.
Jiahai Bai 《Materials Letters》2009,63(17):1485-1488
Novel cobalt oxide doped ZnFe2O4-Fe2O3-ZnO mixed oxides with the Zn/Fe molar ratio of 1/2 were synthesized with a citric acid complex method. The effects of cobalt oxide and calcination temperature on phase composition and photocatalytic activity of the mixed oxides were investigated. X-ray diffraction (XRD) analysis revealed that there were mainly ZnFe2O4, α-Fe2O3, amorphous ZnO and Fe2O3 in the 6 mol% cobalt oxide doped products calcined at 500 °C. 5-10 mol% cobalt oxide doping could significantly enhance the formation of ZnFe2O4 and altered the phase composition of the mixed oxides. Experimental results showed that cobalt oxide doping could remarkably improve the photocatalytic activity of the mixed oxides for phenol degradation. The 6 mol% cobalt oxide doped mixed oxides calcined at 500 °C exhibited better photocatalytic activity as compared with other samples.  相似文献   

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