共查询到20条相似文献,搜索用时 15 毫秒
1.
Carbon free LiFe1−x
Mn
x
PO4 (x = 0, 0.05, 0.1, 0.2, 0.4) cathode materials were prepared by a direct-hydrothermal process at 170 °C for 10 h. The structural
and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy
(SEM), charge–discharge experiments, cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The electrochemical
performance of LiFePO4 prepared in this manner showed to be positively affected by Mn2+-substitution. Among the Mn2+-substitution samples, the LiFe0.9Mn0.1PO4 exhibited an initial discharge capacity of 141.4 mA h g−1 at 0.1 C, and the capacity fading is only 2.7% after 50 cycles. 相似文献
2.
The parameters of the tensor of the electric field gradient (EFG) in cation sites of the La2 ? x Sr x CuO4 lattice have been determined by the method of emission Mössbauer spectroscopy on 57Co(57m Fe), 67Cu(67Zn), 67Ga(67Zn), and 155Eu(155Gd) isotopes. There is no quantitative agreement between the calculated (the pointcharge model) and experimental values of the main component of the tensor EFG V zz , which is explained by the absence of the reliable data on the Sternheimer coefficients for Fe3+, Zn2+, and Gd3+ ions. Based on the comparison of the calculated and experimental dependences of V zz on x it was shown that the holes appearing during the substitution of La3+ for Sr2+ are localized preferably on the oxygen atoms that are in the same plane as the copper atoms, which is in agreement with the model discussed in the literature and assumes that the mechanism responsible for the high-temperature superconductivity of solid solutions La2 ? x Sr x CuO4 is the interaction between the conductivity electrons and two-atomic two-electron centers with negative correlation energy. 相似文献
3.
James Russell Renzas Wenyu Huang Yawen Zhang Michael E. Grass Gabor A. Somorjai 《Catalysis Letters》2011,141(2):235-241
Abstract
Bimetallic 15 nm Pd-core Rh-shell Rh1−x Pd x nanoparticle catalysts have been synthesized and studied in CO oxidation by NO. The catalysts exhibited composition-dependent activity enhancement (synergy) in CO oxidation in high NO pressures. The observed synergetic effect is attributed to the favorable adsorption of CO on Pd in NO-rich conditions. The Pd-rich bimetallic catalysts deactivated after many hours of oxidation of CO by NO. After catalyst deactivation, product formation was proportional to the Rh molar fraction within the bimetallic nanoparticles. The deactivated catalysts were regenerated by heating the sample in UHV. This regeneration suggests that the deactivation was caused by the adsorption of nitrogen atoms on Pd sites. 相似文献4.
Solid solution (AlN) x (SiC)1–x (x = 0.7) was prepared from Al–SiC mixtures by SHS under high pressure of nitrogen gas (50, 70 MPa) and characterized by XRD and SEM. Combustion product was found to have a wurtzite 2H structure with lattice parameters a = 3.10889 ± 0.00022 Å and c = 5.00741 ± 0.00080 Å. 相似文献
5.
E. V. Mikhaleva V. G. Vasil’ev A. P. Nosov E. V. Vladimirova B. V. Slobodin 《Glass Physics and Chemistry》2009,35(1):81-86
Single-phase finely dispersed perovskite-like manganites La1 ? x Sr x MnO3 + δ (0 ≤ x ≤ 0.33) with an average particle size of approximately 3μm were synthesized by the pyrohydrolytic method from a stoichiometric mixture of the corresponding metal nitrates at a temperature of 500°C in a water vapor atmosphere. The parameter δ was changed as a result of the subsequent heat treatment. It was established that the manganite La0.67Sr0.33MnO3 + δ synthesized by the pyrohydrolytic method is characterized by a more pronounced change in the magnetoresistance as compared to the manganite that had the same composition but was synthesized according to the conventional ceramic technique. 相似文献
6.
The absorption edge spectra of vitreous alloys in the As-S-Se system are measured in the temperature range 77–300 K. The parameters of the fundamental absorption edge and the electron-phonon interaction in As40S60 ? x Se x (x = 0–40) glasses are determined, and the influence of the compositional disorder on these parameters is investigated. The contributions of the static structural and temperature disorders to the smearing of the fundamental absorption edge of the alloys under study are evaluated. 相似文献
7.
S. Kh. Estemirova S. G. Titova V. F. Balakirev I. A. Samatov I. L. Sashin 《Glass Physics and Chemistry》2007,33(4):356-361
The specific features revealed in the behavior of the parameters of the crystal structure and the lattice dynamics of the La1 ? x Ca x MnO3 + δ manganites upon the transition to a magnetically ordered state are investigated using X-ray powder diffraction and inelastic neutron scattering. The results obtained are explained in terms of an inhomogeneous state of the samples. This state manifests itself in the form of local regions that are enriched or depleted in charge carriers, with the former regions characterized by the highest temperature of ferromagnetic ordering in the system under investigation. A comparison of the evolution of the crystal structure with variations in the temperature both in the presence and in the absence of a magnetic field has demonstrated that the inhomogeneities are eliminated by an external magnetic field and that the regions enriched in charge carriers become predominant in the system. 相似文献
8.
We report on bifurcate reactions on the surface of well-aligned Si1−x
Ge
x
nanowires that enable fabrication of two different coaxial heterostructure nanowires. The Si1−x
Ge
x
nanowires were grown in a chemical vapor transport process using SiCl4 gas and Ge powder as a source. After the growth of nanowires, SiCl4 flow was terminated while O2 gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized
into SiO2 by the O2 gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O2 pressure without any intermediate region and enables selectively fabricated Ge/Si1−x
Ge
x
or SiO2/Si1−x
Ge
x
coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion
of oxygen through the oxide layer, respectively. 相似文献
9.
E. V. Shkol’nikov 《Glass Physics and Chemistry》2017,43(2):137-145
The kinetics of stepwise transformations during bulk isothermal crystallization of semiconducting AsSe1.5Sn x (x = 0.13, 0.20, 0.28) glasses has been studied in the temperature range of 210?310°С using 119Sn Mössbauer spectroscopy, XPA, and the density and microhardness measurements of the quenched specimens. The kinetics of the gross bulk crystallization of glasses have been analyzed according to the data on density measurement using the Kolmogorov–Avrami equation, which was generalized on stepwise and incomplete isothermal transformations. 相似文献
10.
In many amorphous and liquid semiconductors and other class of materials, the Meyer-Neldel rule is observed in the dc conductivity,
where the preexponential factor (σ0) is found to increase exponentially with the activation energy (ΔE). In the present paper, we report on the observation of the Meyer-Neldel rule in case of ac conductivity at high temperatures
(300–350 K) in bulk samples of glassy Se100 − x
Te
x
(x = 10, 20, 30) alloys. In this temperature range, the approximate variation in ac conductivity with temperature is found to
be exponential and the activation energy is found to vary with frequency. The observation of the Meyer-Neldel rule in the
present study is explained in terms of the compensation effect in the relaxation time.
The text was submitted by the authors in English. 相似文献
11.
R. S. Bubnova E. S. Derkacheva S. K. Filatov V. L. Ugolkov 《Glass Physics and Chemistry》2010,36(1):61-69
Solid solutions K1 − x
Cs
x
BSi2O6 (x (atomic fraction) = 0.00, 0.20, 0.30, 0.35, 0.40, 0.80, 0.90,1.00) have been prepared by solid-phase synthesis and crystallization
of glasses in the KBSi2O6-CsBSi2O6 borosilicate series. The thermal behavior of the solid solutions has been investigated using the annealing and quenching
techniques, dilatometry, and high-temperature X-ray powder diffraction. It has been shown that solid solutions with x = 0.00–0.35 and 0.40–1.00 correspond to space groups I
$
\bar 4
$
\bar 4
3d and I
a
$
\bar 3
$
\bar 3
d, respectively. The cubic-cubic phase transition I
$
\bar 4
$
\bar 4
3d ai Ia
$
\bar 3
$
\bar 3
d occurs in the composition range x = 0.35−0.40 at room temperature. In the series of solid solutions with x = 0−0.30, the reversible cubic-cubic polymorphic transition I
$
\bar 4
$
\bar 4
3d ai ia
$
\bar 3
$
\bar 3
d with an increase in the temperature has been revealed, the temperature of the polymorphic transition has been determined,
and the thermal expansion in both polymorphic modifications has been studied using high-temperature X-ray diffraction and
dilatometry. The solid solutions belonging to the space group Ia
$
\bar 3
$
\bar 3
d are characterized by a lower thermal expansion than the solid solution belonging to the space group I
$
\bar 4
$
\bar 4
3d. According to the calculations, the equivalents α/γ for the space groups I
$
\bar 4
$
\bar 4
3d and Ia
$
\bar 3
$
\bar 3
d are 0.03 and 0.02 (in cesium atomic fractions per degree Celsius), respectively. 相似文献
12.
BaCe0.9−x
Zr
x
Y0.1O3−δ powders were synthesized by a solid-state method at 1,400 °C. Two compositions were studied (x = 0.3 and x = 0.7). Pellets were prepared and conventionally sintered in air at 1,700 °C. Then, the samples were heated at 600 °C for
3 h in different reducing atmospheres: dry hydrogen, wet hydrogen and wet deuterium. After each treatment, the proton diffusion
depth profile was obtained using Secondary Ion Mass Spectroscopy (SIMS). Protons were not incorporated in the material when
the gas was not wet, and the isotope effect suggests that protons present in the pellet come from water and not from hydrogen. 相似文献
13.
Chun-Tao Wang Wen-Kui Zhang Hui Huang Xin-Yong Tao 《Journal of Inorganic and Organometallic Polymers and Materials》2011,21(4):852-857
TiO2−x
N
x
films were deposited on ITO glass by reactive dc magnetron sputtering method under different O2/N2 flow ratios. A NiO film was deposited by chemical bath deposition onto the as-prepared ITO/TiO2−x
N
x
film to form an ITO/TiO2−x
N
x
/NiO composite electrode. The morphology, crystal structure and composition of the TiO2−x
N
x
films were characterized by SEM, XRD and XPS. The photoelectrochemical properties of the TiO2−x
N
x
films were investigated by means of UV–Vis absorption spectra and photocurrent measurements. The results showed that the
TiO2−x
N
x
film sputtered under O2/N2 flow ratio of 1:2 exhibited a higher photocurrent response than the others. Correspondingly, the TiO2−x
N
x
/NiO electrode consisting of the sputtered TiO2−x
N
x
film under O2/N2 flow ratio of 1:2 also showed the best photoelectrochromic feature. 相似文献
14.
The electrochemical properties of amorphous vanadium pentoxide (V2O5) thin films deposited by reactive r.f.-sputtering were investigated using galvanostatic charge/discharge cycling and galvanostatic
intermittent titration technique (GITT). As x in Li
x
V2O5−y
increased (x = 0–2.0), the electromotive force of the lithium (Li)∣1 M LiClO4–propylene carbonate∣Li
x
V2O5−y
cell decreased gradually without a potential plateau or an abrupt potential reduction, demonstrating that an irreversible
structural change did not occur in the entire Li content. Chemical diffusivity of the Li ion in the Li
x
V2O5−y
thin film measured using GITT was determined to be 4 × 10−13–7 × 10−14 cm2 s−1 in the Li content range investigated. 相似文献
15.
L. P. Mezentseva A. V. Osipov V. L. Ugolkov A. A. Akatov V. A. Doilnitsyn T. P. Maslennikova A. V. Yakovlev 《Glass Physics and Chemistry》2018,44(5):440-449
Nanosized powders of orthophosphates in the LaPO4–HoPO4–H2O system have been synthesized to determine the mutual solubility of LaPO4 · nH2O and HoPO4 · nH2O initial components and to obtain ceramic matrices by sintering them. Formation of hexagonal, monoclinic or tetragonal solid solutions was revealed, and their limits and thermal stability were determined. A series of limited hexagonal LaPO4 · nH2O-based solid solutions was observed within the 0 ≤ x ≤ 0.6 concentration range up to 600°C. Further they transformed to monoclinic LaPO4-based form within the 0 ≤ x ≤ 0.3 concentration range. Solubility of LaPO4 · nH2O and LaPO4 in tetragonal HoPO4(· nH2O) is lower (≤10 mol %). Specific surface area of La1–xHoxPO4 · nH2O powders was in the range of 90.5–165.0 m2/g depending on x. Leaching rate of La3+ and Ho3+ from La1–xHoxPO4 matrices in nitric acid solution (pH 1–2) was determined to be 10–5–10–2 g/(cm2 day) for both ions. 相似文献
16.
R. Pereñíguez J. L. Hueso F. Gaillard J. P. Holgado A. Caballero 《Catalysis Letters》2012,142(4):408-416
Abstract
The total oxidation of toluene is studied over catalytic systems based on perovskite with general formula AA′CoO3-δ (A = La, A′ = Sr). The systematic and progressive substitution of La3+ by Sr2+ cations in the series (La1−x Sr x CoO3−δ system) of the perovskites have been studied to determine their influence in the final properties of these mixed oxides and their corresponding reactivity performance for the total oxidation of toluene as a model volatile organic compound with detrimental effects for health and environment. The structure and morphology of the samples before and after reaction have been characterized by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O2 in vacuum and reduction in H2 were also performed to identify the main surface oxygen species and the reducibility of the different perovskites. It is remarkable that the La1−x Sr x CoO3−δ series presents better catalytic performance for the oxidation of toluene, with lower values for the T50 (temperature of 50 % toluene conversion) than the previously studied LaNi1−y Co y O3 series. 相似文献17.
Byeong Sub Kwak No-Kuk Park Jeom-In Baek Ho-Jung Ryu Misook Kang 《Korean Journal of Chemical Engineering》2017,34(7):1936-1943
We investigated the effect of the oxidation state of Mn in CaMnO3 perovskite particles to improve their oxygen transfer performance for chemical-looping combustion (CLC). Li was introduced in the Ca site of CaMnO3 to increase the Mn oxidation state. Ca1?x Li x MnO3 particles were synthesized by the solid-state method, and the amount of Li added ranged from 0 to 0.015 mol. The structure of the synthesized Ca1?x Li x MnO3 particles was examined using XRD, and all particles were confirmed to have a CaMnO3 perovskite structure. The shape and chemical properties of the prepared particles were characterized by using SEM and CH4-TPD. The binding energy and oxidation state of the different elements in the Ca1?x Li x MnO3 particles were measured by XPS. When Li was added, the oxidation state of Mn in Ca1?x Li x MnO3 was higher than that of Mn in CaMnO3. The oxygen transfer performance of the particles was determined by an isothermal H2-N2/air and CH4-CO2/air redox cycle at 850 °C, repeated ten times, using TGA. All particles showed an oxygen transfer capacity of about 8.0 to 9.0 wt%. Among them, Ca0.99Li0.01MnO3 particles had the best performance and the oxygen transfer capacity under H2-N2/air and CH4-CO2/air atmosphere was 8.47 and 8.75 wt%, respectively. 相似文献
18.
Won-Jong Hong Mao Ueda Shinji Iwamoto Saburo Hosokawa Kenji Wada Masashi Inoue 《Catalysis Letters》2012,142(1):32-41
Abstract
Ce–Mn mixed oxides with a Mn/(Ce + Mn) molar ratio of 0.25 were prepared by solvothermal (ST-1) and co-precipitation (CP) methods, and Ba was loaded on the Ce–Mn oxides. In addition, CeO2–MnO x –BaO catalysts with various compositions were directly prepared by the solvothermal (ST-2) method. The NO decomposition activities of these catalysts were examined. Among the catalysts examined, the ST-2 catalyst having a nominal composition of Ce0.8Mn0.15Ba0.05O x exhibited the highest activity; 77% NO conversion to N2 was attained at 800 °C. These catalysts were characterized by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The Raman and XPS results indicate that the CP catalyst had larger amounts of the BaMnO3-δ and/or Mn3O4 phases. The ST-1 and ST-2 catalysts had highly dispersed Ba species on the surface. The ST-2 catalyst had Mn species with the lowest binding energy of Mn 2p and also had a high population of oxygen vacancies in the ceria lattice, suggesting that Mn species with a low oxidation state contributes to the formation of oxygen vacancies, which play an important role in this reaction. 相似文献19.
M. I. Georgievskaya R. S. Bubnova S. K. Filatov V. L. Ugolkov 《Glass Physics and Chemistry》2008,34(4):436-442
Continuous solid solutions and the reversible phase transition from the I-43d cubic phase to the Ia-3d cubic phase are revealed in the borosilicate series K1 ? x Rb x BSi2O6. Samples in the KBSi2O6-RbBSi2O6 system are prepared by solid-phase synthesis and crystallization of glasses and investigated using the annealing and quenching technique, high-temperature X-ray diffraction, and dilatometry. The above polymorphic phase transition is observed in all solid solutions at temperatures in the range from 330 to 430°C depending on the composition: an increase in the rubidium content in the solid solution leads to a gradual decrease in the phase transition temperature. The linear thermal expansion coefficients α are determined for solid solutions of different crystalline modifications and glasses. The linear thermal expansion coefficients α for the I-43d low-temperature phase are equal to (20–23) × 10?6 K?1 according to the X-ray diffraction data and (21–24) × 10?6 K?1 according to the dilatometric data. The values of α for the Ia-3d high-temperature phase lie in the range (4–9) × 10?6 K?1 according to the X-ray diffraction data and in the range (6–9) × 10?6 K?1 according to the dilatometric data. The linear thermal expansion coefficients for both modifications decrease with an increase in the rubidium content in the solid solutions. The linear thermal expansion coefficients for glasses α = (10–11) × 10?6 K?1 are close to those for the high-temperature modification and virtually independent of the sample composition. The I-43d (cubic) ai I41/a (tetragonal) o Ia-3d (cubic) polymorphic phase transitions in the KBSi2O6 compound are revealed by differential scanning calorimetry (DSC) and dilatometry. Their reversibility is confirmed by the DSC data. 相似文献
20.
Lian Mei Chen Qiong Yu Lai Hong Mei Zeng Yan Jing Hao Jian Hua Huang 《Journal of Applied Electrochemistry》2011,41(3):299-305
In this work, effects of drying temperature, pH of aqueous electrolyte and current density on capacitive performance of VO
x
·nH2O material were firstly investigated. VO
x
·nH2O powders were prepared by a melt quenching method. The samples were characterized by X-ray diffraction analysis (XRD) and
Fourier transform infrared (FTIR). The capacitive properties of VO
x
·nH2O samples were examined by cyclic voltammetry and galvanostatic charge/discharge test. VO
x
·nH2O sample which was obtained at the drying temperature of 80 °C, delivers a maximum specific capacitance of 227.3 F g−1 and exhibits excellent capacity retention in the potential range of −0.3 to 0.7 V at a current density of 200 mA g−1 in NaNO3 solution with pH 2. 相似文献