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1.
In the present paper, we describe utilization of cathode active material as anode active material, for example, Li2MnSiO4. The lithium manganese silicate has been successfully synthesized by solid-state reaction method. The X-ray diffraction pattern
confirms the orthorhombic structure with Pmn2
1 space group. The Li/Li2MnSiO4 cell delivered the initial discharge capacity of 420 mA h g−1, which is 110 mA h g−1 higher than graphitic anodes. The electrochemical reversibility and solid electrolyte interface formation of the Li2MnSiO4 electrode was emphasized by cyclic voltammetry. 相似文献
2.
The lead pyrophosphate, Pb2P2O7, compound was prepared by conventional solid-state reaction and identified by X-ray powder diffractometer. Pb2P2O7 has a triclinic structure whose electrical properties were studied using impedance spectroscopy technique. Both impedance
and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature
dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies E
g = 0.66 eV and E
gb = 0.67 eV, respectively. The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation
describes the same mechanism at various temperatures. 相似文献
3.
Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance
and tap density of Li4Ti5O12 and LiFePO4 materials. Spherical Li4Ti5O12/C and LiFePO4/C composites are prepared by spray-drying–solid-state reaction method and controlled crystallization–carbothermal reduction
method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer–Emmett–Teller, alternating
current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing
carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical
properties are obviously improved. The Li4Ti5O12/C and LiFePO4/C composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 g cm−3 and 8.26 m2 g−1 for spherical Li4Ti5O12/C, which are 1.35 g cm−3 and 18.86 m2 g−1 for spherical LiFePO4/C powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li4Ti5O12/C is more than 150 mAh g−1 at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO4/C is close to 140 mAh g−1 at 1.0-C rate. 相似文献
4.
The layered LiNi0.5Mn0.47Al0.03O2 was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The
powders adopted the α-NaFeO2 structure. This substitution of Al for Mn promotes the formation of Li(Ni0.472+Ni0.033+Mn0.474+Al0.033+)O2 structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice
unit cell. The concentration of antisite defects in which Ni2+ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni2+(3a)–Mn4+(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%.
The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with
the combination of Ni2+ (S = 1), Ni3+ (S = 1/2) and Mn4+ (S = 3/2) spin-only values. Delithiation has been made by the use of K2S2O8. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni4+ in the high spin configuration, while Ni2+(3a)–Mn4+(3b) ferromagnetic pairs remain, as the Li+(3b) ions linked to the Ni2+(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn4+ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments. 相似文献
5.
LiCoO2 thin films were prepared by electron beam evaporation technique using LiCoO2 target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10−4 mbar. The films prepared at substrate temperature T
s < 573 K were amorphous in nature, and the films prepared at T
s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron
spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature
range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–eg absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment
exhibit (104) out plane texture with large grains.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006 相似文献
6.
Crystals of the chalcopyrite family, AgGaSe2, AgGaS2, and CdGa2S4, doped with chromium ions have been investigated using high-frequency broad-band EPR spectroscopy in the range 65–530 GHz
at T = 4.2 K. It has been revealed that, in the AgGaSe2 and AgGaS2 crystals, the Cr2+ ions occupy positions with orthorhombic and tetragonal symmetry, whereas the previously investigated CdGaS4 crystals contain only tetragonal centers. The observed spectra have been described in the framework of the spin-Hamiltonian
formalism. Apart from the divalent chromium centers, the EPR lines attributed to non-Kramers ions are observed in the frequency
range 300–450 GHz for all the crystals under investigation. The nature of these lines has been discussed. 相似文献
7.
A. Nucara F. Miletto Granozio M. Radovic F. M. Vitucci P. Maselli R. Fittipaldi A. Vecchione P. Calvani 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):435-441
We measure the transmittance of LaMnO3 (LMO) thin films in the spectral range from 10 000 to 38 000 cm-1 as a function of temperature. The optical conductivity obtained from the transmittance data is decomposed into five Drude-Lorentz
contributions: three of them show evident changes below the Néel temperature T
N
@\simeq 140 K. We discuss the band assignment in the framework of the tight-binding and of the orbitally degenerate Hubbard models.
Our results ascribe the overall low-frequency spectrum of LMO to charge-transfer mechanisms involving the t
2g
and e
g
electrons of the Mn ions, without invoking the presence of excitonic contributions. This finding definitely promotes a Mott-Hubbard
scenario for LMO and provides an estimate of the Hamiltonian parameters. 相似文献
8.
Photopyroelectric spectroscopy of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> - ZnO ceramics
A. Zakaria Z. Rizwan M. Hashim A. Halim Shaari W. Mohmood Mat Yunus 《The European physical journal. Special topics》2008,153(1):33-35
Photopyroelectric spectroscopy is used to study the
band-gap energy of the ceramic (ZnO + xSb2O3), x = 0.1 - 1.5 mol%
and the ceramic (ZnO + 0.4 mol% Bi2O3 + xSb2O3), x = 0 - 1.5 mol% sintered at isothermal temperature, 1280 °C, for 1 and 2 hours. The wavelength of incident light, modulated
at 9 Hz, is kept in the visible range and the photopyroelectric spectrum with
reference to doping level is discussed. The band-gap energy is reduced from
3.2 eV, for pure ZnO, to 2.86, 2.83 eV for the samples without
Bi2O3at 0.1 mol% of Sb2O3 for 1 and 2 hours of
sintering time, respectively. It is reduced to 2.83, 2.80 eV for the samples
with Bi2O3 at 0 mol% of Sb2O3 for 1 and 2 hours of
sintering time, respectively. The steepness factor σA which
characterizes the slop of exponential optical absorption is discussed with
reference to the doping level. The phase constitution is determined by XRD
analysis; microstructure and compositional analysis of the selected areas
are analyzed using SEM and EDX. 相似文献
9.
The electron paramagnetic resonance (EPR) parameters (g
‖ andg
⊥ factors and hyperfine structure constantsA
‖,A
⊥) for Co2+ in Ca(OH)2 are studied from the second-order perturbation formulas on the basis of the cluster approach. In these formulas, the contributions
to EPR parameters from the state interactions and covalency effects are considered and the parameters related to both effects
are obtained from the optical spectra and impurity structure of the studied system. From the study, it is found that the β
angle between the metal-ligand bond and the C3 axis changes from 61° in a pure crystal to 53.68(26)° in the impurity center of a Co2+-doped Ca(OH)2 crystal because of the impurity-induced local lattice relaxation. The reduction of the angle β in the impurity center is
also supported by the result obtained by analyzing the EPR zero-field splitting for Mn2+ in the same Ca(OH)2 crystal. The EPR parameters of Ca(OH)2:Co2+ are also reasonably explained by considering the suitable local lattice relaxation. 相似文献
10.
V. I. Gerasimova A. A. Antoshkov Yu. S. Zavorotny D. A. Lemenovskii 《Journal of Applied Spectroscopy》2012,79(2):203-210
Optical properties (photoluminescence and absorption) of Eu(bta)3(B) n (B = H2O or 1,10-phenanthroline) polycrystalline powders and fluoroacrylate polymers (FAPs) impregnated with these compounds using supercritical CO2 (SC CO2) were investigated. It was established that impregnation of Eu(bta)3phen into the FAPs using an SC CO2 solution was difficult to achieve. The type of B (ancillary ligand) and the polymer matrix were shown to influence the temperature quenching of photoluminescence of Eu3+ ions in the range 25–100°C. A comparative analysis of quantum yields (λex = 300 and 380 nm) and photoluminescence decay times (λex = 337.1 nm) for Eu(bta)3B n and for Eu(bta)3B n -doped FAPs was performed. 相似文献
11.
The electron paramagnetic resonance (EPR) spectra of Ce3+ and Nd3+ impurity ions in unoriented powders of the YBa2Cu3O6.13 compound are observed and interpreted for the first time. It is demonstrated that, upon long-term storage of the samples
at room temperature, the EPR signals of these ions are masked by the spectral line (with the g factor of approximately 2) associated with the intrinsic magnetic centers due to the significant increase in its intensity. 相似文献
12.
Good-quality hexagonal NbSe2 single crystals were prepared. In 2H-NbSe2, superconducting and charge density wave (CDW) transitions were found at T
s = 7.4 K and T
c = 35 K respectively as reported previously. We have noticed that these two transitions are changed to T
c = 42 K and T
s = 6.5 K, in 4H-NbSe2. Thermopower has shown clear anomaly at CDW transitions. The anisotropic upper critical field was calculated as ~3 and 6.3
for 2H- and 4H-single crystals around t = 0.81, where t = T/T
s, from resistivity and explained in terms of coherence length. From the relation, Hc2 (T)=Hc2 (0)[1-t2]H_{\rm c2} (T)=H_{\rm c2} (0)[1-t^2], Hc2l (0)H_{\rm c2}^l (0) was calculated as ~8.15 T and 16.98 T at t = 0.84 in 2H-NbSe2 and 4H-NbSe2 respectively. However, Hc2t (0) = 2.68H_{\rm c2}^t (0) = 2.68T for both single crystals. 相似文献
13.
The preparation of (La9.33−2x/3Sr
x
□0.67−x/3)Si6O24O2 (0 ≤ x ≤ 2) samples with different amounts of cation vacancies is reported. Structure and unit-cell parameters were deduced by Rietveld
analysis of XRD patterns. Structural features that enhance oxygen conductivity in Sr-doped apatites are discussed. Up to three
components were detected in 29Si MAS-NMR spectra which change with the amount and distribution of cation vacancies. In general, oxygen conductivity increases
with the amount of vacancies at La1 (6h) sites, passing through a maximum for x = 0.4. In the case of activation energy, a minimum is detected near x = 1.2, indicating that entropic and enthalpic change in different ways. The presence of cation vacancies should enhance oxygen
hopping along c-axis; however, the analysis of the frequency dependence of conductivity suggests that oxygen motions are produced along three
axes. 相似文献
14.
The effects of dopant on the electrochemical properties of spinel-type Li3.97M0.1Ti4.94O12 (M = Mn, Ni, Co) and Li(4-x/3)CrxTi(5-2x/3)O12(x = 0.1, 0.3, 0.6, 0.9, 1.5) were systematically investigated. Charge-discharge cycling were performed at a constant current
density of 0.5 mA/cm2 between the cut-off voltages of 3.0 and 1.0 V, the experimental results showed that Cr3+ dopant improved the reversible capacity and cycling stability over the pristine Li4Ti5O12. The substitution of the Mn3+ and Ni3+ slightly decreased the capacity of the Li4Ti5O12. Dopants such as Co3+ to some extent worsened the electrochemical performance of the Li4Ti5O12. 相似文献
15.
M.?Cristina?Gon?alves Verónica?de?Zea Bermudez M.?M.?Silva M.?J.?Smith Enrique?Morales Rute?A.?Sá Ferreira Luís?D.?Carlos 《Ionics》2010,16(3):193-201
Variable chain length di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrid networks were prepared by application
of a sol-gel strategy. These materials, designated as di-urethanesils (represented as d-Ut(Y′), where Y′ indicates the average
molecular weight of the polymer segment), were doped with lithium triflate (LiCF3SO3). The two host hybrid matrices used, d-Ut(300) and d-Ut(600), incorporate POE chains with approximately 6 and 13 (OCH2CH2) repeat units, respectively. All the samples studied, with compositions ∞ > n ≥ 1 (where n is the molar ratio of (OCH2CH2) repeat units per Li+), are entirely amorphous. The di-urethanesils are thermally stable up to at least 200 °C. At room temperature the conductivity
maxima of the d-Ut(300)- and d-Ut(600)-based di-urethanesil families are located at n = 1 (approximately 2.0 × 10−6 and 7.4 × 10−5 Scm−1, respectively). At about 100 °C, both these samples also exhibit the highest conductivity of the two electrolyte systems
(approximately 1.6 × 10−4 and 1.0 × 10−3 Scm−1, respectively). The d-Ut(600)-based xerogel with n = 1 displays excellent redox stability. 相似文献
16.
Paramagnetic centers of three types are found in SrF2: Fe(0.2 at. %) crystals. Two types are observed in the untreated crystals, and the third type appears only in the crystals irradiated by x-rays. The EPR spectra of one type of centers in a nonirradiated crystal and of the centers that appear after irradiation are described by the orthorhombic Hamiltonians with an effective spin S eff = 5/2. In both cases, the centers are observed at 4.2 and 77 K. The principal axes of the spin Hamiltonians for them are along the 〈001〉, 〈1 \(\overline 1 \) 0〉, and 〈110〉 axes. However, the fine-structure parameters of their EPR spectra differ significantly. An analysis of the superhyperfine structure (SHFS) of the EPR spectra shows that the radiation center forms through substitution of a Fe2+ ion for a Sr2+ cation. Under x-ray irradiation, the Fe2+ ion transforms into the Fe3+(6 A 1g ) state and is displaced to an off-center position along the C 2 axis of its coordination cube. The absence of a SHFS in the EPR spectra of the orthorhombic centers in a nonirradiated crystal makes it impossible to determine their molecular structure unambiguously. The most probable model is proposed for this structure. The EPR spectra of centers of the third type were observed only at 4.2 K, and the structure of these centers was not studied. 相似文献
17.
V. P. Dyakonov R. Szymczak A. D. Prokhorov E. Zubov A. A. Prokhorov G. Petrakovskii L. Bezmaternikh M. Berkowski V. Varyukhin H. Szymczak 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(3):291-298
Magnetic and electron paramagnetic resonance (EPR) properties of
EuFe3(BO3)4 single crystals have been studied over the
temperature range of 300–4.2 K and in a magnetic field up to 5 T. The
temperature, field and orientation dependences of susceptibility,
magnetization and EPR spectra are presented. An antiferromagnetic ordering
of the Fe subsystem occurs at about 37 K. The easy direction of
magnetization perpendicular to the c axis is determined by magnetic
measurements. Below 10 K, we observe an increase of susceptibility connected
with the polarization of the Eu sublattice by an effective exchange field of
the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the
c axis, we have observed an increase of magnetization at T < 10 K in the
applied magnetic field, which can be attributed to the appearance of the
magnetic moment induced by the magnetic field applied in the basal plane.
According to EPR measurements, the distance between the maximum and minimum
of derivative of absorption line of the Lorentz type is equal to 319 Gs. The
anisotropy of g-factor and linewidth is due to the influence of crystalline
field of trigonal symmetry. The peculiarities of temperature dependence of
both intensity and linewidth are caused by the influence of excited states
of europium ion (Eu3+). It is supposed that the difference between the
g-factors from EPR and the magnetic measurements is caused by exchange
interaction between rare earth and Fe subsystems via anomalous Zeeman
effect. 相似文献
18.
L. K. Aminov A. A. Ershova D. G. Zverev S. L. Korableva I. N. Kurkin B. Z. Malkin 《Applied magnetic resonance》2008,33(4):351-364
Electron paramagnetic resonance (EPR) spectra of doped paramagnetic crystals LiLuF4:U3+ and LiYF4:Yb3+ have been investigated at a frequency of about 9.42 GHz in the temperature range of 10–20 K. The U3+ ion spectrum is characterized by g-factors g
∥ = 1.228 and g
⊥ = 2.516, and contains the hyperfine structure due to the 235U isotope with nuclear spin I = 7/2 and natural abundance of 0.71%. The observed hyperfine interaction constants are A
∥ = 81 G and A
⊥ = 83.8 G. Moreover, the spectrum reveals the well-resolved superhyperfine structure (SHFS) due to two groups of four fluorine
ions forming the nearest surrounding of the U3+ ion. This SHFS contains up to nine components with the spacing between components being about 12.7 G. The SHFS is observed
also in the EPR spectrum of the LiYF4:Yb3+ crystal; up to 17 components with spacing of about 3.7 G may be traced. Some parameters of the effective Hamiltonian of the
SHF interaction are estimated, the contribution of covalent bonding of f-electrons with ligands into these parameters is discussed.
Authors' address: Igor N. Kurkin, Kazan State University, Kremlevskaya ulitsa 18, Kazan 420008, Russian Federation 相似文献
19.
The synthesis and functionalization of carbon nanoparticles with PEG200 and mercaptosuccinic acid, rendering fluorescent carbon dots, is described. Fluorescent carbon dots (maximum excitation and
emission at 320 and 430 nm, respectively) with average dimension 267 nm were obtained. The lifetime decay of the functionalized
carbon dots is complex and a three component decay time model originated a good fit with the following lifetimes: τ
1 = 2.71 ns; τ
2 = 7.36 ns; τ
3 = 0.38 ns. The fluorescence intensity of the carbon dots is affected by the solvent, pH (apparent pK
a of 7.4 ± 0.2) and iodide (Stern-Volmer constant of 78 ± 2 M−1). 相似文献
20.
R. M. Shymkiv S. A. Sveleba I. V. Karpa I. N. Katerynchuk I. M. Kunyo E. I. Phitsych 《Journal of Applied Spectroscopy》2012,78(6):823-828
Optical absorption spectra in thin [N(CH3)4]2CuCl4 crystals in the thickness range 10 μm ≤ d < 100 μm have been studied. Strengthening of the crystal field has been found with
a decrease in the [N(CH3)4]2CuCl4 crystal size. The reasons for absorption band shifts in the visible region depending on the [N(CH3)4]2CuCl4 crystal thickness and the manifestation of a size effect in crystals with an incommensurate superstructure are discussed. 相似文献