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1.
《Solid State Ionics》2006,177(1-2):105-112
Five compositions of Li[Co1 −2x(Li1 / 3Mn2 / 3)x(Ni1 / 2Mn1 / 2)x]O2 solid solutions ( x = 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized using a sol–gel method with three end members of LiCoO2, Li2MnO3(Li[Li1 / 3Mn2 / 3]O2), and Li[Ni0.5Mn0.5]O2. The compositions of metals in transition metal sites were changed to see the effect of them on electrochemical behavior of the solid solutions. All the samples were nano-sized semi-spherical shaped particles with a layered structure. The reduction of cobalt content (the increase of other metals) in the sites increases the lattice parameters, a and c, resulting in the shift of Raman and XRD peak positions. The discharge capacity fading turned serious at higher Co contents, but it was significantly diminished with the decrease of Co content. At lower Co contents, the capacity increased with cycle numbers. The most stable voltage profile was obtained from the composition of Li[Li1 / 15Co3 / 5Ni1 / 10Mn7 / 30]O2 (x = 0.2). 相似文献
2.
《Solid State Ionics》2006,177(26-32):2657-2660
The compounds Li(4−x)/3Mn2(1−x)/3CoxO2 (0 < x < 0.5) were prepared by the sol–gel technique. X-ray diffraction patterns of these compounds were identified as α-NaFeO2 type layered structure, though some super-structure lines, related to the ordered array of Li and transition metal ions in the transition metal layer, were observed. The magnetic susceptibility exhibited an antiferromagnetic transition around 40 K for x < 0.2, however the specimens with x > 0.3 had no magnetic transition. The magnetic percolation may explain these magnetic variations. The electrochemical performances were evaluated for the compound of x = 0.5, and it was seen that the electrochemical properties were sensitive to the potential window. Additionally, it was also found that the discharge capacity strongly depended on the preparation temperature; it took a maximum value at the preparation temperature of 900 °C. The discharge capacity is sensitive not only to the cation mixing degree but also to the particle size. 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.
《Solid State Ionics》2006,177(9-10):863-868
Layered Li(Ni0.5Co0.5)1−yFeyO2 cathodes with 0 ≤ y ≤ 0.2 have been synthesized by firing the coprecipitated hydroxides of the transition metals and lithium hydroxide at 700 °C and characterized as cathode materials for lithium ion batteries to various cutoff charge voltages (up to 4.5 V). While the y = 0.05 sample shows an improvement in capacity, cyclability, and rate capability, those with y = 0.1 and 0.2 exhibit a decline in electrochemical performance compared to the y = 0 sample. Structural characterization of the chemically delithiated Li1−x(Ni0.5Co0.5)1−yFeyO2 samples indicates that the initial O3 structure is maintained down to a lithium content (1 − x) ≈ 0.3. For (1 − x) < 0.3, while a P3 type phase is formed for the y = 0 sample, an O1 type phase is formed for the y = 0.05, 0.1 and 0.2 samples. Monitoring the average oxidation state of the transition metal ions with lithium contents (1 − x) reveals that the system is chemically more stable down to a lower lithium content (1 − x) ≈ 0.3 compared to the Li1−xCoO2 system. The improved structural and chemical stabilities appear to lead to better cyclability to higher cutoff charge voltages compared to that found before with the LiCoO2 system. 相似文献
5.
《Current Applied Physics》2009,9(2):472-477
In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(1 1 1) substrates by metal–organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(1 1 1) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(1 1 1) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 μm. Secondly, the effect of in situ substrate nitridation and the insertion of an SixNy intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the SixNy layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without SixNy layer) and B (with SixNy layer on Si(1 1 1)). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0 0 0 2) diffraction from the GaN epilayer of the sample B in ω-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a SixNy intermediate layer significantly improved the optical and structural properties. In sample C (with SixNy layer on Al0.11Ga0.89N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties. 相似文献
6.
《Solid State Ionics》2006,177(7-8):691-695
Single crystals of the lithium-rich lithium manganese oxide spinels Li1 + xMn2 − xO4 with x = 0.10 and 0.14 have been successfully synthesized in high-temperature molten chlorides at 1023 K. The single-crystal X-ray diffraction study confirmed the cubic Fd3¯m space group and the lattice parameters of a = 8.2401(9) Å for x = 0.10 and a = 8.2273(10) Å for x = 0.14 at 300 K, respectively. The crystal structures have been refined to the conventional values R = 3.7% for x = 0.10 and R = 3.1% for x = 0.14, respectively. Low-temperature single-crystal X-ray diffraction experiments revealed that these single crystal samples showed no phase transition between 100 and 300 K. The electron-density distribution images in these compounds by the single-crystal MEM analysis clearly showed strong covalent bonding features between the Mn and O atoms due to the Mn–3d and O–2p interaction. 相似文献
7.
《Solid State Ionics》2006,177(17-18):1509-1516
The structural and thermal properties of the delithiated LixNi1/3Co1/3Mn1/3O2 (0 < x ≤ 1) material have been investigated by using diffraction and thermoanalytical techniques such as XRD and TG-DSC methods. XRD result shows that the delithiated materials maintain the O3-type structure with defined stoichiometric number at the range of 0.24 < x ≤ 1, exhibiting good crystal structural stability. The cobalt and nickel ions in the delithiated materials change their valence state (i.e. Co3+ to Co4+ and Ni3+ to Ni4+) when x < 0.49; the irreversible changes of the transformation may affect the first cycle of charge–discharge efficiency of the materials. A comparison of the results of TG-DSC with TPD-MS shows that the irreversible change of oxygen species during the delithiation process of LixNi1/3Co1/3Mn1/3O2 have great influence on the structural and thermal stability and reversibility of the materials. 相似文献
8.
Fe3O4 nanoparticles and thin films were prepared on the Au(1 1 1) surface and characterized using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Fe3O4 was formed by annealing α-Fe2O3(0 0 0 1) structures on Au(1 1 1) at 750 K in ultrahigh vacuum (UHV) for 60 min. Transformation of the α-Fe2O3(0 0 0 1) structures into Fe3O4 nanoparticles and thin films was supported by XPS. STM images show that during the growth procedure used, Fe3O4 initially appears as nanoparticles at low coverages, and forms thin films at ~2 monolayer equivalents (MLE) of iron. Two types of ordered superstructures were observed on the Fe3O4 particles with periodicities of ~50 and ~42 Å, respectively. As the Fe3O4 particles form more continuous films, the ~50 Å feature was the predominant superstructure observed. The Fe3O4 structures at all coverages show a hexagonal unit cell with a ~3 Å periodicity in the atomically resolved STM images. 相似文献
9.
Zhongliang Liu Jun Tang Chaoyang Kang Chongwen Zou Wensheng Yan Pengshou Xu 《Solid State Communications》2012,152(11):960-963
Few-layer graphene (FLG) was grown on Al2O3 (0 0 0 1) substrates at different temperatures via direct carbon atoms deposition by using solid source molecular beam epitaxy (SSMBE) method. The structural properties were characterized by reflection high energy electron diffraction (RHEED), Raman spectroscopy and near-edge X-ray absorption fine-structure (NEXAFS). The results showed that the FLG started to form at the substrate temperature of 700 °C. When the substrate temperature increased to 1300 °C, the quality of the FLG was the best and the layer number was estimated to be less than 5. At higher substrate temperature (1400 °C or above), the crystalline quality of the FLG would be deteriorated. Our experiment results demonstrated that the substrate temperature played an important role on the FLG layer formation on Al2O3 (0 0 0 1) substrates and the related growth mechanism was briefly discussed. 相似文献
10.
M. Imaizumi T. Noji T. Adachi Y. Koike 《Physica C: Superconductivity and its Applications》2011,471(21-22):614-617
Annealing effects of FeSe1?xTex (0.6 ≦ x ≦ 1) single crystals have been investigated from measurements of the powder X-ray diffraction and specific heat. Through the annealing, several peaks of powder X-ray diffraction have become sharp and a clean jump of the specific-heat at the superconducting (SC) transition temperature, Tc, has been observed for x = 0.6–0.9, indicating bulk superconductivity. For annealed single-crystals of x = 0.6–0.8, the SC condensation energy, U0, and the SC gap, Δ0, at 0 K have been estimated as ~1.8 J/mol and 2.3–2.5 meV, respectively. The value of 2Δ0/kBTc is 3.9–4.5, indicating a little strong-coupling superconductivity. Both the electronic specific-heat coefficient in the normal state, γn, and the residual electronic specific-heat coefficient in the SC state, γ0, have been found to show significant x dependence. The values of γn are much larger than those estimated from the band calculation. 相似文献
11.
《Solid State Ionics》2006,177(9-10):901-906
Crystal structure, thermal expansion coefficient, electrical conductivity and cathodic polarization of compositions in the system Sm0.5Sr0.5Co1 − xFexO3 − δ with 0 ≤ x ≤ 0.9 were studied as function of Co / Fe ratio and temperature, in air. Two phases, including an Orthorhombic symmetry for 0 ≤ x ≤ 0.4 and a cubic symmetry for 0.5 ≤ x ≤ 0.9, were observed in samples of Sm0.5Sr0.5Co1 − xFexO3 − δ at room temperature. The adjustment of thermal expansion coefficient (TEC) to electrolyte, which is one of the main problems of SSC, could be achieved to lower TEC values with more Fe substitution. High electrical conductivity above 100 S/cm at 800 °C was obtained for all specimens, so they could be good conductors as cathodes of IT-SOFC. The polarization behavior of SSCF as a function of Fe content was evaluated by means of AC impedance using LSGM electrolyte. It was discovered that the Area Specific Resistance (ASR) of SSCF increased as the amount of substitution of Fe for Co increased. When the amount of Fe reached to 0.4, the highest ASR was obtained and then the resistance started decreasing above that. The electrode with a composition of Sm0.5Sr0.5Co0.2Fe0.8O3 − δ showed high catalytic activity for oxygen reduction operating at temperature ranging from 700 to 800 °C. 相似文献
12.
《Solid State Ionics》2006,177(13-14):1205-1210
A comparative investigation of the much-studied La2NiO4+δ (n = 1) phase and the higher-order Ruddlesden-Popper phases, Lan+1NinO3n+1 (n = 2 and 3), has been undertaken to determine their suitability as cathodes for intermediate-temperature solid-oxide fuel cells. As n is increased, a structural phase transition is observed from tetragonal I4/mmm in the hyperstoichiometric La2NiO4.15 (n = 1) to orthorhombic Fmmm in the oxygen-deficient phases, La3Ni2O6.95 (n = 2) and La4Ni3O9.78 (n = 3). High temperature d.c. electrical conductivity measurements reveal a dramatic increase in overall values from n = 1, 2 to 3 with metallic behavior observed for La4Ni3O9.78. Impedance spectroscopy measurements on symmetrical cells with La0.9Sr0.10Ga0.80Mg0.20O3−δ (LSGM-9182) as the electrolyte show a systematic improvement in the electrode performance from La2NiO4.15 to La4Ni3O9.78 with ∼ 1 Ω cm2 observed at 1073 K for the latter. Long-term thermal stability tests show no impurity formation when La3Ni2O6.95 and La4Ni3O9.78 are heated at 1123 K for 2 weeks in air, in contrast to previously reported data for La2NiO4.15. The relative thermal expansion coefficients of La3Ni2O6.95 and La4Ni3O9.78 were found to be similar at ∼ 13.2 × 10− 6 K− 1 from 348 K to 1173 K in air compared to 13.8 × 10− 6 K− 1 for La2NiO4.15. Taken together, these observations suggest favourable use for the n = 2 and 3 phases as cathodes in intermediate-temperature solid-oxide fuel cells when compared to the much-studied La2NiO4+δ (n = 1) phase. 相似文献
13.
《Solid State Ionics》2006,177(17-18):1395-1403
Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1−xInxO3−δ (0.0 ≤ x ≤ 0.75). Analysis of X-ray powder diffraction (XRPD) data reveals that the unit cell parameter, a, increases linearly with an increased Indium concentration. XRPD data was also used to demonstrate the completion of sample hydration, which was reached when the materials showed a set of single-phase Bragg-peaks. Dynamic thermogravimetric analysis (TGA) data showed that approx. 89% of the total number of available oxygen vacancies can be filled in BaZr1−xInxO3−δ for x = 0.50, and that the maximum water uptake occurs below 300 °C. Rietveld analysis of the room temperature neutron powder diffraction (NPD) data confirmed the average cubic symmetry (space group Pm-3m), and an expansion of the unit cell parameter after the hydration reaction. The strong O–H stretch band, 2500–3500 cm− 1, in the infrared absorbance spectrum clearly manifests the presence of protons in the hydrated material. Proton conductivity of hydrated BaZr1−xInxO3−δ, x = 0.75 was investigated during heating and cooling cycles under dry argon atmosphere. The total conductivity during the heating cycle was nearly two orders of magnitude greater than that of cooling cycle at 300 °C, whilst these values were similar at higher temperatures i.e. T > 600 °C. 相似文献
14.
《Solid State Ionics》2006,177(7-8):669-676
The electrical conductivity of sintered samples of Ce1−xNdxO2−x / 2 (0.01 ≤ x ≤ 0.2) was investigated in air as a function of temperature between 150 and 600 °C using AC impedance spectroscopy. The individual contribution of the bulk and grain boundary conductivities has been discussed in detail. In the low temperature range (< 350 °C), the activation enthalpy for bulk conductivity exhibited a shallow minimum at 3 mol% Nd, with a value of 0.68 eV. The activation enthalpy also produced a shallow minimum at 5 mol% Nd in the high temperature range (> 350 °C), with a value of 0.56 eV. It was shown that Ce1−xNdxO2−x / 2 is an electrolyte that obeys the Meyer Neldel rule. The bulk conductivity data measured by others for the same system has also been recalculated and re-evaluated to facilitate easier comparison with our own data. 相似文献
15.
《Solid State Ionics》2006,177(19-25):1837-1841
The cobalt-doped lanthanum–nickel oxide system, La4Ni(3−x)CoxO10±δ (0.0 ≤ x ≤ 3.0, Δx = 0.2), was investigated as possible cathode materials for intermediate-temperature solid-oxide fuel cells. X-ray diffraction shows the presence of two structural phases in the series belonging to Bmab for 0.0 ≤ x ≤ 0.2, 0.8 ≤ x ≤ 2.0 and 2.6 ≤ x ≤ 3.0 and Fmmm for 0.4 ≤ x ≤ 0.6 and 2.2 ≤ x ≤ 2.4. All compositions are oxygen-deficient (δ < 0). Electrical conductivity measurements show a systematic decrease in the conductivity as cobalt content increases from x = 0.0 to 2.0, and reverses for x > 2.0. AC impedance measurements of the x = 0.4 composition in symmetrical cells with LSGM as an electrolyte show improved electrode performance over the parent nickelate La4Ni3O9.78. Long-term thermal stability studies show the x = 0.4 composition to be more stable than the x = 3.0 phase after annealing at 1173 K in air for 1 week making this material a viable candidate for cathodes in solid oxide fuel cells. 相似文献
16.
Theoretical calculations focused on the geometry, stability, electronic and magnetic properties of small palladium clusters Pdn (n=1–5) adsorbed on the NiAl(1 1 0) alloy surface were carried out within the framework of density functional theory (DFT). In agreement with the experimental observations, both Ni-bridge and Al-bridge sites are preferential for the adsorption of single palladium atom, with an adsorption energy difference of 0.04 eV. Among the possible structures considered for Pdn (n=1–5) clusters adsorbed on NiAl(1 1 0) surface, Pd atoms tend to form one-dimensional (1D) chain structure at low coverage (from Pd1 to Pd3) and two-dimensional (2D) structures are more stable than three-dimensional (3D) structures for Pd4 and Pd5. Furthermore, metal-substrate bonding prevails over metal–metal bonding for Pd cluster adsorbed on NiAl(1 1 0) surface. The density of states for Pd atoms of Pd/NiAl(1 1 0) system are strongly affected by their chemical environment. The magnetic feature emerged upon the adsorption of Pd clusters on NiAl(1 1 0) surface was due to the charge transfer between Pd atoms and the substrate. These findings may shade light on the understanding of the growth of Pd metal clusters on alloy surface and the construction of nanoscale devices. 相似文献
17.
《Journal of magnetism and magnetic materials》2002,247(3):296-304
Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (Ts) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at Ts between 200°C and 330°C were single crystals. Amorphous films were observed at Ts below 200°C and it was not possible to deposit films at Ts above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at Ts above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at Ts between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad. 相似文献
18.
Maike Lübbe Alexander M. Gigler Robert W. Stark Wolfgang Moritz 《Surface science》2010,604(7-8):679-685
We report on the identification of Fe3O4 (magnetite) and α-Fe2O3 (hematite) in iron oxide thin films grown on α-Al2O3(0 0 0 1) by evaporation of Fe in an O2-atmosphere with a thickness of a few unit cells. The phases were observed by Raman spectroscopy and confirmed by X-ray diffraction (XRD). Magnetite appeared independently from the substrate temperature and could not be completely removed by post-annealing in an oxygen atmosphere as observed by X-ray diffraction. In the temperature range between 400 °C and 500 °C the X-ray diffraction shows that predominantly hematite is formed, the Raman spectrum shows a mixture of magnetite and hematite. At both lower and higher substrate temperatures (300 °C and 600 °C) only magnetite was observed. After post-annealing in an O2-atmosphere of 5 × 10?5 mbar only hematite was detectable in the Raman spectrum. 相似文献
19.
We have studied by Spot Profile Analysis Low Energy Electron Diffraction (SPA-LEED) and Auger Electron Spectroscopy (AES) Ni–Al alloyed layers formed by annealing, around 780 K, Al deposits on a stepped Ni(1 1 1) surface. The surface structure and composition of the thin epitaxial Ni3Al and NiAl films, obtained respectively below and above a critical Al initial coverage θc, differ markedly from those of corresponding bulk alloys.The Ni3Al ordered films form in a concentration range larger than the stability domain of the L12 Ni3Al phase. The NiAl films present a marked distortion with respect to the lattice unit cell of the B2 NiAl phase, which slowly decreases when the film thickness increases.It also appears that the value of θc depends on the morphology of the Ni(1 1 1) substrate, increasing from θc = 4.5 ML for a flat surface to θc = 10 ML for a surface with a miscut of 0.4°. This could be directly related to the presence of steps, which favour Ni–Al interdiffusion. 相似文献
20.
Tomoki Tsumura Koichiro Tsumori Goichi Shimizu Masahiro Toyoda 《Journal of Physics and Chemistry of Solids》2012,73(2):237-244
Spinel-type manganese oxide/porous carbon (Mn3O4/C) nanocomposite powders have been simply prepared by a thermal decomposition of manganese gluconate dihydrate under an Ar gas flow at above 600 °C. The structure and texture of the Mn3O4/C nanocomposite powders are investigated by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) equipped scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), selected area-electron diffraction (SA-ED), thermogravimetric and differential thermal analysis (TG-DTA) and adsorption/desorption of N2 gas at ?196 °C. The electrochemical properties of the nanocomposite powders in 1 M KOH aqueous solution are studied, focusing on the relationship between their structures and electrochemical capacitance.In the nanocomposite powders, Mn3O4 nano particles approximately 5 nm in size are dispersed in a porous carbon matrix. The nanocomposite powders prepared at 800 °C exhibit a high specific capacitance calculated from cyclic voltammogram of 350 and 600 F g?1 at a sweep rate of 1 and 0.1 mV s?1, respectively. The influence of the heating temperature on the structure and the electrochemical properties of nanocomposite powders is also discussed. 相似文献