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1.
Superfine Li1−xMn2O4−σ powders were successfully synthesized by the alcohol-thermal method using 0.01 mol of MnO2, 0.01mol of LiOH·H2O, and 0.06mol of NaOH as starting materials at 160-200°C. The products are characterized by XRD, TEM, ED, BET, and ICP. Results show that the Li0.74Mn2O3.74 powder prepared at 200°C has an average size of 180 nm with BET surface areas of 16.44 m2/g. A possible formation mechanism is proposed. It was concluded that the alcohol acts not only as the solvent but also as the reducing agent in the synthesis of Li1−xMn2O4−σ powders. The effects of reaction temperature and the contents of NaOH and LiOH on the formation of single phase Li1−xMn2O4−σ were investigated.  相似文献   

2.
Incommensurately modulated structure of the composite crystal InCr1−xTixO3+x/2 was refined by the profile fitting of powder X-ray diffraction based on the four-dimensional superspace group. The crystal consists of two monoclinic subsystems mutually incommensurate in b. The first subsystem is the alternate stacking of an edge-shared InO6 octahedral layer and a Cr/Ti triangle-lattice plane along c*. A sheet of oxygen atoms constructing the second subsystem is also extending on the Cr/Ti plane. The whole structure is the alternate stacking of an edge-shared InO6 octahedral layer and a Cr/Ti-O plane, where displacive modulation of O ions is prominent. Metal ions on the Cr/Ti-O plane are surrounded by three or four oxygen ions on the plane and, in addition, two axial ones.  相似文献   

3.
The structure of pseudorhombohedral-type InFe1−xTixO3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO3-In2Ti2O7 including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P21/a is the alternate stacking of an edge-shared InO6 octahedral layer and an Fe/Ti-O plane along c*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10−4 S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.  相似文献   

4.
MgO and Co1−xO powders in 9:1 and 1:9 molar ratio (denoted as M9C1 and M1C9, respectively) were sintered and homogenized at 1600°C followed by annealing at 850°C and 800°C, respectively to form defect clusters and precipitates. Analytical electron microscopic observations indicated the protoxide remained as rock salt structure with complicated planar diffraction contrast for M9C1 sample, however with spinel paracrystal precipitated from the M1C9 sample due to the assembly of charge- and volume-compensating defects of the 4:1 type, i.e., four octahedral vacant sites surrounding one Co3+-filled tetrahedral interstitial site. The spacing of such defect clusters is 4.5 times the lattice spacing of the average spinel structure of Mg-doped Co3−δO4, indicating a higher defect cluster concentration than undoped Co3−δO4. The {111} faulting of Mg-doped Co3−δO4/Co1−xO in the annealed M1C9 sample implies the possible presence of zinc blend-type defect clusters with cation vacancies assembled along oxygen close packed (111) plane.  相似文献   

5.
The influence of Bi3+ on the structural and magnetic properties of the rare-earth-containing perovskites REFe0.5Mn0.5O3 (RE=La,Nd) was studied, and the limit of bismuth substitution was determined to be x≤0.5 in BixRE1−xFe0.5Mn0.5O3+δ (RE=La,Nd) at ambient pressure. Crystal structures in both La and Nd series were determined to be GdFeO3-type Pnma with the exception of the Bi0.3La0.7Fe0.5Mn0.5O3 sample, which is monoclinic I2/a in the abb tilt scheme. The samples undergo a transition to G-type antiferromagnetic order along with a weak ferromagnetic component, mixed with cluster-glass type behavior. The substitution of bismuth into the lattice results in a drop in TN relative to the lanthanide end-members. Long range ordering temperatures TN in the range 240-255 K were observed, with a significantly lower ordered magnetic moment in the case of lanthanum (M∼1.7-1.9 μB) than in the case of neodymium (M∼2.1 μB).  相似文献   

6.
Zhuyi Wang 《Acta Physico》2008,24(3):375-378
The nanocrystalline LaCoxFe1-xO3 with different concentrations of Co was prepared by polyethylene glycol (PEG) sol-gel method and characterized by differential thermal analysis and thermal gravimetric analysis (DTA-TGA), X-ray diffraction (XRD), and scanning electron microscope (SEM). It was found that the crystal structure of perovskite-type could be obtained at 600 °C, and the concentration of Co had significant effects on the solid-state reaction and the average particle size of the obtained nanocrystals. Furthermore, the humidity-sensitive properties of nanocrystalline LaCoxFe1-xO3 were investigated, and it was found that LaCo0.3Fe0.7O3 exhibited higher sensitivity to humidity compared with other samples. The addition of Na2CO3 improved the humidity-sensitive properties of this sample, and made its response to humidity good in the whole humidity range of 11%-95% relative humidity (RH).  相似文献   

7.
A reagentless signal-on electrochemiluminescence (ECL) biosensor for DNA hybridization detection was developed based on the quenching effect of ferrocene (Fc) on intrinsic cathodic ECL at thin oxide covered glassy carbon (C/CxO1−x) electrodes. To construct the DNA biosensor, molecular beacon (MB) modified with ferrocene (3′-Fc) was attached to a C/CxO1−x electrode via the covalent bound between labeled amino (5′-NH2) and surface functional groups. It was found that the immobilization of the probe on the electrode surface mainly depended on the fraction of surface carbonyl moiety. When a complementary target DNA (cDNA) was present, the stem-loop of MB on the electrode was converted into a linear double-helix configuration due to hybridization, resulting in the moving away of Fc from the electrode surface, and the restoring of the cathodic ECL signal. The restoration of the ECL intensity was linearly changed with the logarithm of cDNA concentration in the range of 1.0 × 10−11 to 7.0 × 10−8 M, and the detection limit was ca. 5.0 pM (S/N = 3). Additionally, single-base mismatched DNA can be effectively discriminated from the cDNA. The great advantage of the biosensor lies in its simplicity and cost-effective with ECL generated from the electrode itself, and no adscititious luminophore is required.  相似文献   

8.
Paracrystalline array of defect clusters ca. five times the lattice spacing of the average Co3−δO4 spinel structure occurred more or less in a relaxed manner when the sintered Co1−xO polycrystals were air-quenched below the Co1−xO/Co3−δO4 transition temperature to activate oxy-precipitation of cube-like Co3−δO4 at dislocations. The same paracrystalline spacing was obtained for Co3−δO4 when formed via oxidizing/sintering the Co1−xO powders at 800°C in air, suggesting a nearly constant δ value for Co3−δO4 in the T-PO2 conditions encountered. The extra cobalt vacancies and Co3+ interstitials, as a result of δ value, may form additional 4:1-derived defect clusters for further paracrystalline distribution in the spinel lattice. The nanosize defect clusters self-assembled by columbic interactions and lattice relaxation in ionic crystal may have potential applications as step-wise sensor of oxygen partial pressure at high temperatures.  相似文献   

9.
The phase transition behavior of perovskite-type compounds, La1−xSrxCrO3, was investigated by differential scanning calorimetry (DSC), dilatometry, dc magnetic susceptibility measurement and X-ray diffraction analysis. Both second-order magnetic phase transition from antiferromagnetic to paramagnetic and first-order structural phase transition from orthorhombic to rhombohedral were observed in the DSC or dilatometric curve of every specimen. The temperatures of both these magnetic and structural phase transitions decreased linearly with an increase in Sr content. The structural phase transition temperature of La1−xSrxCrO3 with x less than 0.11 is higher than the magnetic phase transition temperature; however, a larger decrease in structural phase transition temperature than in magnetic phase transition temperature was observed with an increase in Sr content, resulting in a structural phase transition temperature lower than the magnetic phase transition temperature for La1−xSrxCrO3 with x of more than 0.12. It was also observed that the heat of absorption of the structural phase transition decreased with an increase in x. In the dependence of dc magnetic susceptibility on temperature, variations by not only magnetic but also structural phase transitions were observed. It was also revealed that thermal expansion coefficient is affected not only by structural phase transition but also magnetic phase transition. Magnetic and structural phase diagram of La1−xSrxCrO3, suggesting the existence of two Sr contents and temperatures at which triple phases coexist, was proposed.  相似文献   

10.
The single-phase region of La1−xSrxCrO3 (x=0.1, 0.2, 0.3) was precisely determined as a function of temperature, PO2 and Sr content. The powders with the nominal composition of La1−xSrxCrO3 were equilibrated under various conditions, and then identified by XRD analyses. To confirm the equilibration, two independent experiments were performed for each composition observing (i) the precipitation of the second phase from a single-phase solid solution, and (ii) the formation of the single phase from the constituent oxides. Two kinds of second phases, SrCrO4 and an unknown phase, were observed depending on the conditions. The second phases tended to appear at low temperature, in high PO2 and with a large Sr content. The single-phase regions obtained via the two equilibration routes were in good agreement with each other. The thermodynamic calculations on the supposition of ideality of the solid solution essentially reproduced the experimental results. When this material is used as the interconnects of solid oxide fuel cells, much attention should be paid to its relatively narrow solubility range of Sr; for example, the solubility limit is approximately 0.1 under a typical cathode-side condition (1273 K, air).  相似文献   

11.
The synthesis and structural properties of Mg1−xMn2+xO4, for 0≤x≤1 are described. Complete miscibility in the solid state exists for this system. For the material with the correct stoichiometry, i.e. MgMn2O4, the effect of temperature on the cation distribution was investigated= above 600°C the inversion degree (m) starts increasing. The electrical conductivity shows a small dependence on P(O2) which is consistent with the small oxygen non-stoichiometry determined by means of thermogravimetry. The main contribution to the transport properties arises from the inversion equilibrium. Two distinct conductivity regimes, below and above the inversion threshold, can be assumed to explain the electrical conductivity and thermoelectric power results.  相似文献   

12.
Several compounds of the (Na1−xLix)CdIn2(PO4)3 solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd2+ in the M(1) site, and of In3+ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na+ and Li+ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na+→Li+ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na1−xLix)MnFe2(PO4)3, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.  相似文献   

13.
Lithium substituted Li1+xMn2−xO4 spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na2O·4MoO3 at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn3+ to Mn4+ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn3+ to Mn4+ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.  相似文献   

14.
纳米微孔NixZn(1-x)Fe2O4的水热合成研究   总被引:9,自引:0,他引:9  
0引言尖晶石型铁酸盐是一类重要的磁性材料,它可用于防止电磁波辐射设备以及隐身材料中的吸波剂犤1,2犦,具有价格低廉、吸波性能优良的特点。同时尖晶石型铁酸盐也是一类重要的催化剂,90年代初又发现了氧缺位的该类化合物具有将CO2还原为C的优良催化性能犤3犦。因此,有关铁酸盐的制备及性能研究一直是化学工作者和材料科学工作者感兴趣的领域。随着新的合成方法的不断涌现,对传统铁氧体材料进行结构改造以提高其性能是一个重要的研究发展方向,本文采用模板剂造孔技术,首次在NixZn(1-x)Fe2O4水热合成中选用模板剂,…  相似文献   

15.
采用水热合成法制备了Co3O4及复合Ag/Co3O4、CuO/Co3O4一维纳米产品。用XRD,FE-SEM和TEM手段对产品进行了表征。采用循环伏安法研究了合成产品修饰的玻碳电极在碱性溶液中对对硝基苯酚的电催化还原性能。与裸玻碳电极相比,1mmol·L-1的对硝基苯酚在用Co3O4、特别是CuO/Co3O4修饰的玻碳电极上还原的峰电流明显增大,用Ag/Co3O4(Ag/Co原子比分别为1∶5和2∶5)修饰的玻碳电极催化还原对硝基苯酚时,尽管还原峰电流增大不是太大,但其峰电位明显降低(分别降低0.265和0.371V)。  相似文献   

16.
This paper describes the results of electron microscopy, high-temperature powder neutron diffraction, and impedance spectroscopy studies of brownmillerite-structured Ba2In2O5 and perovskite structured Ba(InxZr1−x)O3−x/2. The ambient temperature structure of Ba2In2O5 is found to adopt Icmm symmetry, with disorder of the tetrahedrally coordinated (In3+) ions of the type observed previously in Sr2Fe2O5. Ba2In2O5 undergoes a ∼6-fold increase in its ionic conductivity over the narrow temperature range from ∼1140 K to ∼1230 K, in broad agreement with previous studies. This transition corresponds to a change from the brownmillerite structure to a cubic perovskite arrangement with disordered anions. Electron microscopy investigations showed the presence of extended defects in all the crystals analyzed. Ba(InxZr1−x)O3−x/2 samples with x=0.1 to 0.9 adopt the cubic perovskite structure, with the lattice parameter increasing with x.  相似文献   

17.
Polycrystalline samples with general formula Yb2−xCrxO3 (0<x<0.03), obtained by sol-gel method and analyzed by X-ray diffraction, formed solid solutions over all the mentioned range. Cr showed a maximum solubility of 2.8 mol% in Yb2O3 sesquioxide at 1000 °C. A preferential substitution of Cr3+ ions over two cationic sites, 8b and 24d in the space group Ia-3 was found. The lattice parameters a are found to vary linearly (10.4402(4) Å <a<10.4372(1) Å) with the composition x. The two independent atoms Yb/Cr have octahedral coordination; however, the degrees of distortion of their coordination polyhedron are different. Replacing Yb3+ by Cr3+ introduces slight changes in the atomic coordinates leading to an increase of the mean cation-anion distances. The ability of Raman spectroscopy to detect changes in local coordination is utilized. A pseudo-tetrahedral coordination for the Cr3+ in the 24d site was found. Magnetic susceptibility measurements of all samples were done in a temperature range of 2-50 K. For T<37 K, the inverse paramagnetic susceptibilities depend linearly on temperature. However, in the high-temperature region, for T>37 K, the inverse paramagnetic susceptibilities are non-linear versus temperature. This deviation from the Curie-Weiss behaviour was discussed.  相似文献   

18.
Bi2Fe4O9 nanoparticles were prepared at low temperature via a facile, one-step hydrothermal synthesis process using iron(Ⅲ) nitrate nonahydrate(Fe(NO3)3·9H2O) and bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) as starting materials and sodium hydroxide (NaOH) as the precipitant and mineralizer. XRD results indicate that the as-prepared nanoparticles are pure Bi2Fe4O9. SEM images reveal that the as-prepared Bi2Fe4O9 nanoparticles have a sheet-like morphology. The Bi2Fe4O9 nanoparticles thus obtained are paramagnetic at room temperature as shown by magnetic measurements.  相似文献   

19.
PMMA/Ni0.5Zn0.5Fe2O4 nanocomposite with superparamagnetic behavior was synthesized by in situ emulsion polymerization of methylmethacrylate (MMA) monomer in the presence of Ni0.5Zn0.5Fe2O4 colloidal suspension assisted by ultrasonic irradiation. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). XRD and FT-IR spectra confirmed the formation of PMMA/Ni0.5Zn0.5Fe2O4 nanocomposite. TEM images showed that Ni0.5Zn0.5Fe2O4 nanoparticles with the particle sizes of about 12 nm were well dispersed in the polymer matrix. The nanocomposite at room temperature exhibited superparamagnetic behavior under applied magnetic field. The formation mechanism of PMMA/Ni0.5Zn0.5Fe2O4 nanocomposite was proposed as well.  相似文献   

20.
Laser ablation of CeO2 target in vacuum (5×10−4 Pa) was used to produce nanometer-size condensates, which deposited as yellowish top coating and whitish bottom coating on a soda-lime glass substrate. The top coating consists of optically anisotropic columnar domains conformable to monoclinic Ce6O11 phase coexisting with cubic (c) CeO2−x, whereas the bottom coating is optically isotropic c-CeO2−x due to oxygen uptake from the substrate. Transmission electron microscopy indicated that the columnar domains are made up of defective fluorite-type nanoparticles, which tended to coalesce over (111) plane to form dislocations and (111)-preferred orientation, an artificial epitaxy owing to rotation-coalescence of (111) faceted CeO2−x condensates on the amorphous substrate and/or within the coating.  相似文献   

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