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1.
Detailed electrochemical investigations have been carried out on LiNi0.8Co0.17Al0.03O2 as cathode materials for lithium ion batteries in the potential range of 2.8-4.3 V. This sample showed an initial discharge capacity of 186 mAh/g which corresponds to 67% of its theoretical capacity. The effect of addition of LiCoO2 to LiNi0.8Co0.17Al0.03O2 in the ratio 10:90, 30:70, 50:50 has been studied. The results showed that the addition of LiCoO2 has improved the working voltage of the cell. In addition, the percentage retention (95%) of the cell is significantly increased in the composition ratio 50:50.  相似文献   

2.
The Gd doped ceria (CGO) in thin layers is of great interest for low temperature operation. In the present investigation, we report on the use of spray pyrolysis technique for the synthesis of CGO thin films. The process parameters were optimized for synthesizing Gd0.1Ce0.9O1.95 films. Films were characterized by XRD, EDS, SEM, and AFM and are observed to be phase pure and dense with surface roughness of the order of ∼5 nm. The d.c. conductivity was also measured and is observed to be ∼0.5 S/cm at 623 K.  相似文献   

3.
The Bi0.9Sb0.1 powders were prepared by mechanical alloying and then pressed under 6 GPa at different pressing temperatures. X-ray diffraction spectra showed that the single phase was formed. The nanostructure of grain was observed by bright-field imaging. Electrical conductivity, Seebeck coefficient, and thermal conductivity had been investigated in the temperature range of 80-300 K. The absolute Seebeck coefficient value of 120.3 μV/K was measured at 130 K. The figure-of-merit reached a maximum value of 0.90×10−3 K−1 at 140 K.  相似文献   

4.
Lattice dynamics of lithium iron orthophosphate (LiFePO4) isostructural with olivine have been investigated using the first-principles calculations taking into account the on-site Coulomb interaction within the GGA + U scheme. Born effective charge tensors, phonon frequencies at the Brillouin zone center and phonon dispersion curves are calculated and analyzed. The Born effective charge tensors exhibit anisotropy, which gives a convincing evidence for the one-dimensional Li migration tunnel along the [010] direction in LiFePO4, which has been proposed by other theoretical calculations and experimental observation. The calculated phonon frequencies at the Γ point of the Brillouin zone show good agreement with the available experimental observations.  相似文献   

5.
Two batches of poly-crystalline lithium manganate were prepared by a fuel assisted solution combustion method. LiMn2O4(S) was prepared using starch as the fuel and LiMn2O4(P) was prepared using poly vinyl alcohol (PVA) as the fuel. XRD studies indicated a significant and consistent shift in the 2θ values of all the hkl peaks to higher values in LiMn2O4(P) compared to LiMn2O4(S) indicating a lattice contraction in the former. TG/DTA studies indicated a higher formation temperature (∼25 °C higher) for LiMn2O4(P). The higher formation temperature most likely promotes the oxidation of some Mn3+ to Mn4+ with a lower ionic radius causing a lattice contraction. This hypothesis is confirmed through XPS studies which indicated the presence of a higher fraction of Mn4+ in LiMn2O4(P) than that present in LiMn2O4(S). A crystal shape algorithm was used to generate the crystal habits of lithium manganate from their XRD data leading to an understanding on the exposed hkl planes in these materials. From the atomic arrangement on the exposed hkl planes it is predicted that LiMn2O4(P) would be less prone to manganese dissolution and hence would possess a higher cycle life when compared to LiMn2O4(S).  相似文献   

6.
In order to study the dynamic properties of LixMn2O4, potential relaxation techniques (PRT) is used to measure the chemical diffusion coefficient of LixMn2O4. Results are presented for x ranges from x=0.1 to 0.9. They show that the chemical diffusion coefficient at the two-phase coexistent stage near x=0.3 and 0.7 is higher than at the single-phase stage during the insertion and extraction process. Monte Carlo (MC) simulations are also used to simulate the ionic conductivity σ of Li ions in LixMn2O4 and its dependence as a function of lithium concentration x. The results show an M shaped curve in the plot of ionic conductivity σ versus x when the simulation temperature is 293 K, which confirms the experimental PRT results. The voltage profiles of LixMn2O4/Li cells were also simulated with different boundary conditions.  相似文献   

7.
Migration of small polarons in λ-MnO2, Li0.5Mn2O4 and LiMn2O4 is studied via first principles calculations. Migration energy barriers of single small polaron migrations in λ-MnO2, Li0.5Mn2O4 and LiMn2O4 are 0.22 eV, 0.45 eV and 0.35 eV, respectively. The energy level changes of Mn-3d states along the polaron migration path are analyzed in detail. Results indicate that the activation energy barrier of polaron migration is strongly associated with the energy level shift of Mn-3dz2 orbital, which is dependent on the short range structural arrangement of Mn3+/Mn4+ in the crystal. The electrical conduction properties of LixMn2O4 at room temperature are then discussed.  相似文献   

8.
Spherical-shaped Li4Ti5O12 anode powders with a mean size of 1.5 μm were prepared by spray pyrolysis. The precursor powders obtained by spray pyrolysis had no peaks of crystal structure of Li4Ti5O12. The powders post-treated at temperatures of 800 and 900 °C had the single phase of spinel Li4Ti5O12. The powders post-treated at a temperature of 1000 °C had main peaks of the Li4Ti5O12 phase and small impurity peaks of Li2Ti3O7. The spherical shape of the precursor powders was maintained after post-treatment at temperatures below 800 °C. The Brunauer-Emmett-Teller (BET) surface areas of the Li4Ti5O12 anode powders post-treated at temperatures of 700, 800 and 900 °C were 4.9, 1.6 and 1.5 m2/g, respectively. The initial discharge capacities of Li4Ti5O12 powders were changed from 108 to 175 mAh/g when the post-treatment temperatures were changed from 700 to 1000 °C. The maximum initial discharge capacity of the Li4Ti5O12 powders was obtained at a post-treatment temperature of 800 °C, which had good cycle properties below current densities of 0.7 C.  相似文献   

9.
The deposition of gadolinia-doped ceria (CGO, Gd0.1Ce0.9O1.95) and LaGaO3-based perovskite oxides (LSGM, La0.9Sr0.1Ga0.8Mg0.2O2.87) thin films on a stainless steel substrate was studied using the electrostatic spray deposition (EDS) technique. The effect of process conditions, such as deposition temperature, deposition time and liquid flow rate, on the surface morphology and microstructure of thin films was examined with scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The deposited CGO films with a highly porous and three-dimensional interconnected structure were obtained at a liquid flow rate of 0.5 ml/h, a deposition temperature of 503 K and a deposition time ranging from 0.5 to 1 h. On the other hand, the deposited LSGM thin films with porous microstructure were also obtained at the deposition time of 1 h, the deposition temperature of 533 K and the liquid flow rate of 0.5 ml/h. The deposited CGO and LSGM thin films were amorphous at the used deposition temperature. Subsequently, the samples were annealed at 1173 K for 2 h and the desired crystal structures were obtained. The chemical analysis of the thin films was investigated by energy dispersive X-ray (EDX) analysis. The observed chemical compositions of the samples were in a fair agreement with those of the starting solutions.  相似文献   

10.
Thin films of ZnWO4 and CdWO4 were prepared by spray pyrolysis and the structural, optical, and luminescence properties were investigated. Both ZnWO4 and CdWO4 thin films showed a broad blue-green emission band. The broad band of ZnWO4 films was centered at 495 nm (2.51 eV) consisted of three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 540 nm (2.30 eV). The broad band of CdWO4 films at 495 nm (2.51 eV) could be decomposed to three bands at 444 nm (2.80 eV), 495 nm (2.51 eV) and 545 nm (2.28 eV). These results are consistent with emission from the WO66− molecular complex. The luminance and efficiency for ZnWO4 film at 5 kV and 57 μA/cm2 were 48 cd/m2 and 0.22 lm/w, respectively, and for CdWO4 film the values were 420 cd/m2 and 1.9 lm/w.  相似文献   

11.
Three different VO2 (B) nanostructures, including urchin-like VO2 (B), VO2 (B) honeycombs and VO2 (B) nanorods have been successfully fabricated through hydrothermal process by adjusting the concentrations of the oxalic acid. The microstructure and morphology of the VO2 nanostructures were evaluated by using X-ray diffraction and scanning and transmission electron microscopies. Electrochemical properties measurements of urchin-like VO2 (B) and VO2 (B) honeycombs showed excellent cycling performance, especially the urchin-like VO2 (B) exhibited higher discharge capacity and better capacity retention.  相似文献   

12.
The effects of the precursor types of Ni and Fe components on the morphology, mean size, and magnetic property of NiFe2O4 powders prepared by spray pyrolysis from the spray solution, with citric acid were studied. The precursor powders with hollow and thin wall structure turned to the nano-sized NiFe2O4 powders after post-treatment at a temperature of 800 °C. The nickel ferrite powders obtained from the spray solution with ferric chloride had nanometer sizes and narrow size distributions irrespective of the types of nickel precursor. The nickel ferrite powders obtained from the spray solution with ferric nitrate and nickel chloride also had nanometer size and narrow size distribution. The saturation magnetizations of the NiFe2O4 powders changed from 37 to 42 emu/g according to the types of the Fe and Ni precursors. The saturation magnetizations of the NiFe2O4 powders increased with increasing the Brunauer-Emmett-Teller (BET) surface areas of the powders.  相似文献   

13.
Present investigation reports, spray pyrolytic deposition of Mn: Co3O4 thin films onto the stainless steel by spray pyrolysis, at the deposition temperature 573 ± 2 K via aqueous route. Prepared electrodes were characterized structurally and morphologically by means of XRD and SEM. Also optical and electrochemical characterizations were carried out in depth. Structural characterization confirms face centered cubic and tetragonal body centered crystal structures for Co3O4 and Mn3O4 respectively. The rough granular morphology is observed form SEM. Electrochemical study reveals the pseudo capacitive as well as double layer behavior with optimum specific capacitance 485.29 F/g at the scan rate 1 mV/s in 1 M KOH electrolyte. Specific energy, specific power and columbic efficiency were calculated using chronopotentiometric technique. Electrochemical impedance spectroscopy was carried out in the frequency range 1 mHz–1 MHz. Randles equivalent circuit parameters associated with the operative cell are reported.  相似文献   

14.
We present a first-principles investigation of the crystal and electronic structure as well as the average insertion voltage of the Li-site (by Na and Cr) and metal-site (by isovalent Ni, Zn, Ca, Mg and Mn and aliovalent Cu, Al, In, Mo and Zr) doped LiCoPO4. The results show that both the Li-site doping and metal-site doping may reduce the volume change of the material during Li extraction/reinsertion process. The metal doped at Li-site will block the path of Li ion diffusion. The doping by aliovalent transition metals will introduce defect levels in the energy band. It could influence the conductivity insertion voltage.  相似文献   

15.
In this paper we present magneto-optical studies, viz., domain imaging by Faraday contrast, on the diluted Ising antiferromagnet Fe0.9Mg0.1Cl2. The metamagnetic domain structure observed within the mixed antiferro-paramagnetic phase below the tricritical temperature (Tt) in applied fields Hc1HaHc2 depends on time and history. Memory of position and shape of antiferromagnetic domains, which first grow from the more magnetized phase by field decreasing, is preserved even after cycling through Ha = 0 as a consequence of random-field induced nano-domain structures. The extremely slow relaxation of magnetization in the conjectured spin-glass phase, just above Hc2, is discussed as a possible origin for the memory effect in this region.  相似文献   

16.
Thin films of molybdenum trioxide (MoO3) were deposited on common glass using the chemical spray pyrolysis technique. A (NH4)6Mo7O244H20 solution 0.1 M was used as the precursor one. The influence of substrate temperature on the crystallographic structure, surface morphology and electrical behavior of MoO3 thin films was studied. MoO3 can exist in two crystalline forms, the thermodynamically stable orthorhombic α-MoO3 and the metastable monoclinic β-MoO3 phase. XRD-spectra showed a growth of α-MoO3 phase percentage as substrate temperature increases from 420 K up to 670 K. Films deposited in the 500–600 K range have a clearly porous surface structure of nanometer order as can be seen in SEM images. Changes up to six magnitude orders were observed in MoO3 thin films electrical resistance when films temperature varied from 100 K up to 500 K. The sensing property of these MoO3 films was also studied. The sensitivity was investigated in the temperature range 160 and 360 K for H2O and CO gases, respectively. Both of them are of reducing nature. In all studied cases sensitivity decreases slowly as film temperature is raised. At room temperature the sensitivity changes from 12 up to 75% depending on substrate temperature. The sensitivity for CO gas was found to be lower than that of H2O.  相似文献   

17.
Spray pyrolysis technique has been employed successfully for the synthesis of single phase mixed valence spinel hausmannite (Mn3O4) thin films using alcoholic start solution of manganese acetate (Mn(CH3COO)2·4H2O) on pyrex glass substrates at atmospheric pressure using air as a carrier gas. Thermal decomposition of the precursor in the temperature range 320-490 °C led to the formation of Mn3O4 phase as revealed from the thermogravimetry analysis. Prepared samples are characterized by X-ray diffraction that shows spinel structure with space group I41/amd. Pure and well crystallized specimen is subjected to X-ray photoelectron spectroscopy for the surface chemistry investigation of these systems at a molecular level. Surface Mn/O ratio is compared to the bulk composition of the sample. Atomic force micrographs revealed that the morphology and the surface grains of the films largely influenced by the substrate temperature.  相似文献   

18.
Orthorhombic CsH2PO4 undergoes a ferroelectric transition at Tc = ?119.5°C, whereas the ferroelectric transition temperature in isomorphous CsD2PO4 is Tc = ?5.55°C. The transitions are of first order in both cases. The rather large isotope effect demonstrates the importance of the OHO bonds in the transition mechanism.  相似文献   

19.
Uniform and adherent cobalt oxide thin films have been deposited on glass substrates from aqueous cobalt chloride solution, using the solution spray pyrolysis technique. Their structural, optical and electrical properties were investigated by means of X-ray diffraction (XRD), scanning electron micrograph (SEM), optical absorption and electrical resistivity measurements. Along with this, to propose Co3O4 for possible application in energy storage devices, its electrochemical supercapacitor properties have been studied in aqueous KOH electrolyte. The structural analysis from XRD pattern showed the oriented growth of Co3O4 of cubic structure. The surface morphological studies from scanning electron micrographs revealed the nanocrystalline grains alongwith some overgrown clusters of cobalt oxide. The optical studies showed direct and indirect band gaps of 2.10 and 1.60 eV, respectively. The electrical resistivity measurement of cobalt oxide films depicted a semiconducting behavior with the room temperature electrical resistivity of the order of 1.5 × 103 Ω cm. The supercapacitor properties depicted that spray-deposited Co3O4 film is capable of exhibiting specific capacitance of 74 F/g.  相似文献   

20.
Mn4+-rich perovskite manganites (nominal composition: Pr0.1Ca0.9MnO3) were synthesized by using a citric acid method and sintered at different temperatures (800, 900, 1000, and 1300 °C) to adjust the concentration of charge carrier. All the samples are found to be in the cluster glass state at low temperature, as indicated by dc and ac magnetization. With the increase of sintering temperature, the ferromagnetic component in samples increases at first, and attains a maximum at 1000 °C, then decreases again at 1300 °C, which could be well interpreted by the change of charge carrier concentration induced by nonstoichiometry, consistent with the trend on the phase diagram. However, nonstoichiometry breaks long-range Mn-O-Mn interaction, resulting in the variance from the phase diagram.  相似文献   

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