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1.
《Solid State Ionics》2006,177(3-4):333-341
A study of LiFePO4-based electrodes prepared through various synthesis conditions is presented. From X-Ray diffraction, high resolution transmission electron microscopy, electrochemical Li+ extraction/insertion and electrical conductivity data we conclude that the use of starting precursors such as Li2CO3, FeC2O4·2H2O and/or Nb(OC6H5)5 produces LiFePO4-based composites containing significant amounts of carbon. We never succeeded in doping LiFePO4 with Nb to yield Li1−xNbxFePO4 but produced, instead, crystalline β-NbOPO4 and/or an amorphous (Nb, Fe, C, O, P) “cobweb” around LiFePO4 particles which is responsible for superior electrochemical activity. AC-conductivity measurements conclude to a total electrical conductivity of ∼10 9 S cm 1 at 25 °C with an activation energy of ca. 0.65 eV for pure LiFePO4 and LiFePO4/β-NbOPO4 composites. C-containing LiFePO4 samples, including those that were tentatively but unsuccessfully doped with Nb, are much more conductive (up to 1.6 · 10 1 S cm 1) with an activation energy ΔE∼0.08 eV.  相似文献   

2.
A joint chemical reactor system referred to as an ultrasonic-intensified micro-impinging jetting reactor (UIJR), which possesses the feature of fast micro-mixing, was proposed and has been employed for rapid preparation of FePO4 particles that are amalgamated by nanoscale primary crystals. As one of the important precursors for the fabrication of lithium iron phosphate cathode, the properties of FePO4 nano particles significantly affect the performance of the lithium iron phosphate cathode. Thus, the effects of joint use of impinging stream and ultrasonic irradiation on the formation of mesoporous structure of FePO4 nano precursor particles and the electrochemical properties of amalgamated LiFePO4/C have been investigated. Additionally, the effects of the reactant concentration (C = 0.5, 1.0 and 1.5 mol L−1), and volumetric flow rate (V = 17.15, 51.44, and 85.74 mL min−1) on synthesis of FePO4·2H2O nucleus have been studied when the impinging jetting reactor (IJR) and UIJR are to operate in nonsubmerged mode. It was affirmed from the experiments that the FePO4 nano precursor particles prepared using UIJR have well-formed mesoporous structures with the primary crystal size of 44.6 nm, an average pore size of 15.2 nm, and a specific surface area of 134.54 m2 g−1 when the reactant concentration and volumetric flow rate are 1.0 mol L−1 and 85.74 mL min−1 respectively. The amalgamated LiFePO4/C composites can deliver good electrochemical performance with discharge capacities of 156.7 mA h g−1 at 0.1 C, and exhibit 138.0 mA h g−1 after 100 cycles at 0.5 C, which is 95.3% of the initial discharge capacity.  相似文献   

3.
《Solid State Ionics》2006,177(26-32):2617-2624
The paper presents the investigations on the structural, electrical and electrochemical properties of Mn substituted phospho-olivines LiFe1  yMnyPO4 and of W, Ti or Al doped LiFePO4. The microscopic nature of the observed macroscopic, metallic-like conductivity of W, Ti, Al doped phospho-olivine samples is discussed. Some fundamental arguments against the bulk type conductivity are presented.A single phase, diffusional mechanism of deintercalation was found to appear for Mn-substituted LiFe1  yMnyPO4 samples in the whole range of lithium concentration, in contrast to the pure LiFePO4, LiMnPO4 and W, Ti, Al doped phospho-olivines, where a two-phase mechanism of electrochemical lithium extraction/insertion is observed.  相似文献   

4.
Nanoscale Co3O4 particles were doped into MgB2 tapes with the aim of developing superconducting wires with high-current-carrying capacity. Fe-sheathed MgB2 tapes with a mono-core were prepared using the in situ powder-in-tube (PIT) process with the addition of 0.2–1.0 mol% Co3O4. The critical temperature decreased monotonically with an increasing amount of doped Co3O4 particles for all heat-treatment temperatures from 600 to 900 °C. However, the transport critical current density (Jc) at 4.2 K varied with the heat-treatment temperatures. The Jc values in magnetic fields ranging from 7 to 12 T decreased monotonically with increasing Co3O4 doping level for a heat-treatment temperature of 600 °C. In contrast, some improvements on the Jc values of the Co3O4 doped tapes were observed in the magnetic fields below 10 T for 700 and 800 °C. Furthermore, Jc values in all the fields measured increased as the Co3O4 doping level increase from 0 to 1 mol% for 900 °C. This heat-treatment temperature dependence of the Jc values could be explained in terms of the heat-treatment temperature dependence of the irreversibility field with Co3O4 doping.  相似文献   

5.
New solid electrolytes containing acetamide and lithium bioxalato borate (LiBOB) with different molar ratios have been investigated. Their melting points (Tm) are around 42 °C. The ionic conductivities and activation energies vary drastically below and above Tm, indicating a typical feature of phase transition electrolyte. The ionic conductivity of the LiBOB/acetamide electrolyte with a molar ratio of 1:8 is 5 × 10? 8 S cm? 1 at 25 °C but increases to 4 × 10? 3 S cm? 1 at 60 °C. It was found that anode materials, such as graphite and Li4Ti5O12, could not discharge and charge properly in this electrolyte at 60 °C due to the difficulty in forming a stable passivating layer on the anodes. However, a Li/LiFePO4 cell with this electrolyte can be charged properly after heating to 60 °C, but cannot be charged at room temperature. Although the LiBOB/acetamide electrolytes are not suitable for Li-ion batteries due to poor electrode compatibility, the current results indicate that a solid electrolyte with a slightly higher phase transition temperature than room temperature may find potential application in stationary battery for energy storage where the electrolyte is at high conductive liquid state at elevated temperature and low conductive solid state at low temperature. The interaction between acetamide and LiBOB in the electrolyte is also studied by Raman and FTIR spectroscopy.  相似文献   

6.
Iron-doped nickel oxide (Fe0.01Ni0.99O, abbreviated as FNO) nanoparticles were prepared by sol–gel process using 1,3-propanediol as a solvent and also as a chelating agent, and calcined at the various temperatures (400–1000 °C) for 2 h. The phase composition and the microstructure of the calcined products were investigated by X-ray diffraction and scanning electron microscopy techniques, respectively. Magnetic properties were measured at room temperature using a vibrating sample magnetometer. All calcined samples showed the single phase of FNO cubic rock-salt structure without the presence of any impurity phases. The crystallite size from XRD and particle size from SEM increased as calcining temperature increased. The FNO powders calcined at 400?600 °C revealed the uniform and dense spherical particles in nanosize. The room-temperature ferromagnetism was observed for all samples. When the calcining temperature was increased, the saturation magnetization decreased whereas the coercivity increased, corresponding to the less dense and larger particles. The calcined sample at 400 °C had the best magnetic properties with the highest Ms of 5.34 emu/g (at 10 kOe) and the lowest Hc of 372 Oe.  相似文献   

7.
The YBCO films with BaSnO3 (BSO) particles were prepared on LAO (0 0 1) substrates by metal organic deposition using trifluoroacetates (TFA-MOD) via introducing SnCl4 powders into the YBCO precursor solution. It was found that with the increase of the SnCl4 contents, the slower decomposition and higher temperature for nucleation during the reaction were requested compared to that of pure YBCO film. The YBCO films with different contents of Sn with dense surface and well c-alignment were obtained under optimized heat treatment, and the BaSnO3 phases were detected by XRD analysis. Litter effect of BSO particles on the Tc and Jc values of YBCO films was found. All YBCO films with BSO particles had Tc values over 90 K and Jc values over 1 MA/cm2. A significant enhancement of Jc was observed for YBCO films with BSO particles compared to that of pure YBCO film by the field dependence of Jc values. The best property was obtained for YBCO film with 6 mol.% Sn at 77 K under magnetic field. The results showed that the Jc value of YBCO film with 6 mol.% Sn was enhanced by a factor of 2 in 2 T, and over a factor of 10 beyond 4 T compared to that of pure YBCO film.  相似文献   

8.
A highly crystalline LiFePO4/C phase was successfully synthesized by a microwave irradiation method in 4 min. SEM and particle size analysis indicate that the particle size of resulting LiFePO4/C is much smaller than that of the solid-state derived sample and that it mostly distributes in the range of 160–600 nm. Cycling tests show that the sample prepared by microwave method can deliver 150 mAh g? 1 at 17 mA g? 1(0.1C). Further AC impedance measurements reveal that the LiFePO4 electrode can be well activated after the first cycle as reflected by the dramatic decrease in the charge transfer resistance.  相似文献   

9.
An attempt to prepare a metalorganic precursor of gallium with reactivity at low temperature in chemical vapor deposition (CVD) systems was done by reacting N-methylpyrrolidine with metal gallium or gallium nitrate under mild conditions. The precursors were bubbled into a CVD assemblage and then reacted with ammonia at temperatures between 400 and 700 °C. The depositions onto silicon substrates were pyramidal particles of 100 nm width at the base and up to 55 nm in height. The rise in growth temperature increased particle density from 0.9 to 27.1 particles per square micron, but reduced the height from 50 to 10 or 2 nm. XPS spectra showed the presence of gallium and nitrogen. The intensity of the gallium spectrum decreased as the process temperature increased indicating that GaNx particles were deposited rather than the stoichiometric gallium nitride (GaN). An additional N1s band of impurities appeared whose intensity increases with the reaction temperature. The lower impurity content corresponded to the sample prepared with Ga(NO3)3 at 400 °C.  相似文献   

10.
Composites containing La0.8Sr0.2Cr1 ? xRuxO3 ? δ (LSCrRu) with x = 0–0.25 and Gd0.1Ce0.9O1.95 (GDC) were studied as anodes in solid oxide fuel cells (SOFCs) with La0.9Sr0.1Ga0.8Mg0.2O3 ? δ (LSGM) electrolytes. Electrode polarization resistance RP decreased during initial SOFC operation before reaching a minimum. The decrease was more rapid, and the ultimate RP value reached was generally lower, with increasing temperature and Ru content x. RP was stable at longer times except for x = 0.25 where it increased slightly. SOFCs with x = 0.18 anodes at 800 °C yielded power densities as high as 0.53 W/cm2 with an RP value, including the (La,Sr)(Co,Fe)O3–GDC cathode, of < 0.15 Ω cm2. Transmission electron microscopy revealed Ru nano-particles on LSCrRu surfaces; their size increased and their density decreased with increasing temperature. Increasing the Ru content increased the density of Ru surface particles at a given time and temperature. Measured early-stage Ru surface coverage values were consistent with a model where Ru supply to the LSCrRu surface was limited by Ru bulk out-diffusion, but the coverage saturated at longer times. There was surprisingly little Ru particle coarsening over times up to 1000 h at 800 °C, with Ru particles sizes remaining < 10 nm. The cell RP values generally decreased with increasing Ru nano-particle surface area.  相似文献   

11.
Nanosized copper aluminate (CuAl2O4) spinel particles have been prepared by a precursor approach with the aid of ultrasound radiation. Mono-phasic copper aluminate with a crystallite diameter of 17 nm along the (3 1 1) plane was formed when the products were synthesized using Cu(NO3)2·6H2O and Al(NO3)3·9H2O as starting materials, with urea as a precipitation agent at a concentration of 9 M. The reaction was carried out under ultrasound irradiation at 80 °C for 4 h and a calcination temperature of 900 °C for 6 h. The synthesized copper aluminate particles and the effect of different processing conditions such as the copper source, precipitation agents, sonochemical reaction time, calcination temperature and time were analyzed and characterized by the techniques of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Fourier transformation infrared spectroscopy (FT–IR).  相似文献   

12.
Cavitation holds the promise of a new and exciting approach to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure. The collapse process occurs supersonically and generates a host of physical and chemical effects. We have made an attempt to fabricate natural cellulose material using hydrodynamic as well as acoustic cavitation. The cellulose material having initial size of 63 micron was used for the experiments. 1% (w/v) slurry of cellulose sample was circulated through the hydrodynamic cavitation device or devices (orifice) for 6 h. The average velocity of the fluid through the device was 10.81 m/s while average pressure applied was 7.8 kg/cm2. Cavitation number was found to be 2.61. The average particle size obtained after treatment was 1.36 micron. This hydrodynamically processed sample was sonicated for 1 h 50 min. The average size of ultrasonically processed particles was found to be 301 nm. Further, the cellulose particles were characterized with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to see the effect of cavitation on crystallinity (Xc) as well as on melting temperature (Tm). Cellulose structures consist of amorphous as well as crystalline regions. The initial raw sample was 86.56% crystalline but due to the effect of cavitation, the crystallinity reduced to 37.76%. Also the melting temperature (Tm) was found to be reduced from 101.78 °C of the original to 60.13 °C of the processed sample. SEM images for the cellulose (processed and unprocessed) shows the status and fiber–fiber alignment and its orientation with each other. Finally cavitation has proved to be very efficient tool for reduction in size from millimeter to nano scale for highly crystalline materials.  相似文献   

13.
The well defined microstructures of BiPO4 were successfully synthesized by the facile hexamethylenetetramine (HMT) assisted hydrothermal method. The low temperature monoclinic BiPO4 structure with space group P21/n, were obtained from X-ray diffraction (XRD) for the pristine and HMT-assisted BiPO4 with 1, 3, 5 and 10 mmole concentration. A transformation from low temperature monazite-type phase to the high temperature SbPO4-type phase of BiPO4 was observed at the 10 mmole concentration. There was a variation in the morphology from polyhedron to octahedra-like and finally into cube shape upon an increase in concentration of HMT. The role of reaction time in the morphology of BiPO4 particles was investigated. The selected area electron diffraction (SAED) pattern elucidated the ordered dot pattern and the calculated d-spacing revealed the formation of BiPO4. An increased specific capacitance of HMT assisted materials (202 F/g) compared with pristine BiPO4 (89 F/g) at 5 mA/cm2 was observed upon morphological variation due to HMT addition.  相似文献   

14.
SrY2−x(MoO4)4:Er3+/Yb3 phosphors with doping concentrations of Er3+ and Yb3+ (x = Er3+ + Yb3+, Er3+ = 0.05, 0.1, 0.2 and Yb3+ = 0.2, 0.45) have been successfully synthesized by a cyclic microwave-modified sol–gel method, and the upconversion photoluminescence properties have been investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of 1–3 μm. Under excitation at 980 nm, SrY2(MoO4)4:Er3+/Yb3+ particles exhibited a strong 525-nm, weak 550-nm emission bands in the green region, and a very weak 655-nm emission band in the red region. The possible mechanism of the green and red emissions was discussed in detail under consideration of a two-photon process. The Raman spectra of the particles indicated the presence of strong peaks at both higher and lower frequencies.  相似文献   

15.
The layered nanocrystalline NH4MnPO4·H2O was obtained by grinding MnSO4·H2O and (NH4)3PO4·3H2O in the presence of surfactant PEG-400 via a solid-state reaction at room temperature, maintaining the mixture at room temperature for 12 h, washing the mixture with water, and drying at 60 °C. The resulting NH4MnPO4·H2O and its products of thermal decomposition were characterized using thermogravimetry and differential thermal analyses (TG/DTA), IR, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV–vis, and magnetic susceptibility. The data showed that when dried at 60 °C for 5 h, highly crystallized orthorhombic NH4MnPO4·H2O (space group Pmnm(59)) was obtained with an average particle size of 45 nm and an average interlayer distance of 0.8701 nm. On the other hand, monoclinic nanocrystalline Mn2P2O7 with space group C2/m(12) was obtained when the product was calcined at 600 °C for 3 h. Magnetic susceptibility measurements from room temperature to 2.5 K point to ferrimagnetic ordering at TN~17 K.  相似文献   

16.
A novel spatial composition spread approach was used successfully to deposit a 52-member library of La2?xSrxCuO4 (0 ? x ? 0.18) using magnetron sputtering combined with physical masking techniques. Two homemade targets of La2CuO4 and La1.82Sr0.18CuO4 were sputtered at a power of 41 W RF and 42 W DC, respectively, in a process gas of 15 mTorr argon. The libraries were sputtered onto LaSrAlO4 (0 0 1), SrTiO3 (1 0 0) and MgO (1 0 0) substrates through a 52-slot shadow mask for which a ?20 V substrate bias was applied to prevent resputtering. The resulting amorphous films were post-annealed (800 °C for 1 h then at 950 °C for 2 h) in a tube sealed with oxygen gas. Wavelength Dispersive Spectroscopy (WDS) analysis revealed the expected linear variation of Sr content from 0 to 0.18 with an approximate change of 0.003 per library member. Transport measurements revealed superconducting transitions as well as changes in the quasiparticle scattering rate. These transitions and scattering rate changes were mapped to produce the T-hole concentration phase diagram.  相似文献   

17.
《Ultrasonics sonochemistry》2014,21(4):1284-1288
TiO2–WO3 heterostructures were synthesized at room temperature, ambient pressure, and short reaction time via a sonochemical approach. TEM and EDX images show that the prepared TiO2–WO3 heterostructures consist of globular agglomerates (∼250 nm in diameter) composed of very small (<5 nm) dense particles (WO3) dispersed inside the globules. The observed less intense monoclinic WO3 diffraction peak (around 2θ = 22° belonging to (0 0 1) plane) and the high intense hexagonal WO3 diffraction peak (around 2θ = 28° belonging to (2 0 0) plane) in XRD indicate that there may be phase transition occurring due to the formation of intimate bond between TiO2 and WO3. In addition, the formation of such new phase was also observed from Raman spectra with a new peak at 955 cm−1, which is due to the symmetric stretching of W = O terminal. The catalytic activity of TiO2–WO3 heterostructures was tested for the degradation of wastewater pollutant containing Tergitol (NP-9) by a process combined with ozonation and it showed two-fold degradation rate compared with ozone process alone.  相似文献   

18.
《Solid State Ionics》2006,177(11-12):1021-1025
Raman and Fourier transform infrared measurements for LixM0.03Fe0.97PO4, M = Cr, Cu, Al, Ti were performed. The spectra for delithiated samples to a low content of lithium extraction are practically the same as those of LiFePO4. For a high content of lithium extraction, the spectra repeat that of FePO4. In the case of the Li0.11FePO4 oxide the spectra cannot be reproduced just by the superposition of the end member profiles. An additional broad band contribution is found in both Raman and infrared spectra probably due to a disordered structure present in the mixture. This suggests that the well accepted two-phase model for the delithiation process in LiFePO4 is incorrect. The model should be revised to include the new phase as detected here for a particular level of lithium extraction close to that of complete oxidation of the Fe2+ ions to Fe3+.  相似文献   

19.
Synthesis of scorodite (FeAsO4·2H2O) using dynamic action agglomeration and the oxidation effect from ultrasound irradiation was investigated. The effect of different reaction temperatures (90, 70, 50, and 30 °C) on the size and morphology of scorodite particles synthesized under O2 gas flow and ultrasound irradiation was explored because the generation of fine bubbles depends on the solution temperature. At 90 °C, the size of scorodite particles was non-homogeneous (from fine particles (<1 μm) to large particles (>10 μm)). The oxidation–reduction potential (ORP) and yield at 90 °C showed lower values than those at 70 °C. The scorodite particles, including fine and non-homogeneous particles, were generated by a decrease in the oxidation of Fe(II) to Fe(III) and promotion of dissolution caused by the generation of radicals and jet flow from ultrasound irradiation. Using ultrasound irradiation in the synthesis of scorodite at low temperature (30 °C) resulted in the appearance of scorodite peaks in the X-ray diffraction (XRD) pattern after a reaction time of 3 h. The peaks became more intense with a reaction temperature of 50 °C and crystalline scorodite was obtained. Therefore, ultrasound irradiation can enable the synthesis of scorodite at 30 °C as well as the synthesis of large particles (>10 μm) at higher temperature. Oxide radicals and jet flow generated by ultrasound irradiation contributed significantly to the synthesis and crystal growth of scorodite.  相似文献   

20.
In order to enhance the superconductive properties of the high temperature superconductors, nanoparticles acting as pinning centers can be intentionally introduced into the structure by chemical doping. In this study, a Dy-doped YBa2Cu3O7?x (YBCO) coated conductor, prepared by a metal organic decomposition process, was investigated to determine the size, composition and 3D distribution of the nanoparticles. It was found that the addition of Dy results in the formation of a high density of secondary phase nanoparticles of composition (YsDy1?s)2Cu2O5 with s  0.6. A tomographic tilt series was acquired by using a scanning transmission electron microscope to analyze the interaction between the particles and the structural defects and to determine the 3D distribution of nanoparticles. For the investigated sample volume (0.06 μm3), 71 particles were located with a particle size distribution ranging between 13 and 135 nm with an average size of ~30 nm. The distribution uniformity, position and the size of the particles are observed to be dependent on the interaction of the particles with the twin boundaries. It is observed that the larger particles are generally located on more than one twin boundary, moreover, the particle size is smaller on the twin boundaries shared by several particles. This suggests that the growth of the particles is determined by fast twin boundary diffusion and the formation of the large particles might be prevented by altering the temperature–time parameters of the production processing to enhance the flux pinning characteristic of the superconductors by achieving a more uniform size of flux pinning centers.  相似文献   

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