共查询到20条相似文献,搜索用时 23 毫秒
1.
To improve the cycle performance of spinel LiMn2O4 as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM
x
Mn2 − x
O4 (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe0.05M
y
Mn1.95 − y
O4 (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray
diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure
without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM
x
Mn2 − x
O4 (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe0.05M
y
Mn1.95 − y
O4 (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn2O4 spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed
to the stabilization in the spinel structure by the doped metal cations. 相似文献
2.
Lead-free (Bi0.98−x
La0.02Na1−x
)0.5Ba
x
TiO3 ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties
have been studied. The results of X-ray diffraction show that La2+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at
0.04<x<0.10. Compared with pure Bi0.5Na0.5TiO3 ceramics, the (Bi0.98−x
La0.02Na1−x
)0.5Ba
x
TiO3 ceramics possess much smaller coercive field E
c and larger remanent polarization P
r. Because of the low E
c (3.38 kV/mm), large P
r (46.2 μC/cm2) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly
enhanced at x=0.06: d
33=181 pC/N and k
p=36.3%. The depolarization temperature T
d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation
disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties
suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T
d. 相似文献
3.
Pasquale D’Angelo Pablo Stoliar Tobias Cramer Antonio Cassinese Francesco Zerbetto Fabio Biscarini 《Applied Physics A: Materials Science & Processing》2009,95(1):55-60
A dynamic method for quantifying the amount and mechanism of trapping in organic field effect transistors (OFETs) is proposed.
It exploits transfer characteristics acquired upon application of a triangular waveform gate sweep V
G. The analysis of the transfer characteristics at the turning point V
G=−V
max between forward and backward gate sweeps, viz. around the maximum gate voltage V
max applied, provides a differential slope Δm which depends exclusively on trapping. Upon a systematic change of V
max it is possible to extract the initial threshold voltage, equivalent to one of the observables of conventional stress measurements,
and assess the mechanism of trapping via the functional dependence on the current. The analysis of the differential logarithmic
derivative at the turning point yields the parameters of trapping, as the exponent β and the time scale of trapping τ. In the case of an ultra-thin pentacene OFET we extract β=1 and τ=102–103 s, in agreement with an exponential distribution of traps. The analysis of the hysteresis parameter Δm is completely general and explores time scales much shorter than those involved in bias stress measurements, thus avoiding
irreversible damage to the device. 相似文献
4.
I. Ruiz de Larramendi R. López-Antón J. I. Ruiz de Larramendi T. Rojo 《Applied Physics A: Materials Science & Processing》2008,93(3):655-661
Polycrystalline samples of Pr1−x
Sr
x
Fe0.8Co0.2 O3−δ
(x=0.1, 0.2, 0.3) (PSFC) were prepared by the combustion synthesis route at 1200°C. The structure of the polycrystalline powders
was analysed with X-ray powder diffraction data. The X-ray diffraction (XRD) patterns were indexed as the orthoferrite similar
to that of PrFeO3 having a single-phase orthorhombic perovskite structure (Pbnm). Pr1−x
Sr
x
Fe0.8Co0.2O3−δ
(x=0.1, 0.2, 0.3) films have been deposited on yttria-stabilized zirconia (YSZ) single-crystal substrates at 700°C by pulsed
laser deposition (PLD) for application to thin film solid oxide fuel cell cathodes. The structure of the films was analysed
by XRD, scanning electron microscopy (SEM) and atomic force microscopy (AFM). All films are polycrystalline with a marked
texture and present pyramidal grains in the surface with different size distributions. Electrochemical impedance spectroscopy
(EIS) measurements of PSFC/YSZ single crystal/PSFC test cells were conducted. The Pr0.7Sr0.3Fe0.8Co0.2O3−δ
film at 850°C presents a lower area specific resistance (ASR) value, 1.65 Ω cm2, followed by the Pr0.8Sr0.2Fe0.8Co0.2O3−δ
(2.29 Ω cm2 at 850°C) and the Pr0.9Sr0.1Fe0.8Co0.2O3−δ
films (5.45 Ω cm2 at 850°C). 相似文献
5.
The stoichiometry range and lithium ion conductivity of Li5+x
Ba
x
La3−x
Ta2O12 (x = 0, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with garnet-like structure were studied. The powder X-ray diffraction data
of Li5+x
Ba
x
La3−x
Ta2O12 indicated that single phase oxides with garnet-like structure exist over the compositional range 0 ≤ x ≤ 1.25; while for x = 1.5, 1.75 and 2.00, the presence of second phase in addition to the major garnet like phase was observed. The cubic lattice
parameter increases with increasing x and reaches a maximum at x = 1.25 then decreases slightly with further increase in x in Li5+x
Ba
x
La3−x
Ta2O12. The impedance plots of Li5+x
Ba
x
La3−x
Ta2O12 samples obtained at 33 °C indicated a minimum grain-boundary resistance (R
gb) contribution to the total resistance (R
b + R
gb) at x = 1.0. The total (bulk + grain boundary) ionic conductivity increases with increasing lithium and barium content and reaches
a maximum at x = 1.25 and then decreases with further increase in x in Li5+x
Ba
x
La3−x
Ta2O12. Scanning electron microscope investigations revealed that Li6.25Ba1.25La1.75Ta2O12 is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li6.25Ba1.25La1.75Ta2O12 exhibits the highest total (bulk + grain boundary) and bulk ionic conductivity of 5.0 × 10−5 and 7.4 × 10−5 S/cm at 33 °C, respectively. 相似文献
6.
T. Mills L. G. Kaake X.-Y. Zhu 《Applied Physics A: Materials Science & Processing》2009,95(1):291-296
Electrolytes are finding applications as dielectric materials in low-voltage organic thin-film transistors (OTFT). The presence
of mobile ions in these materials (polymer electrolytes or ion gels) gives rise to very high capacitance (>10 μF/cm2) and thus low transistor turn-on voltage. In order to establish fundamental limits in switching speeds of electrolyte gated
OFETs, we carry out in situ optical spectroscopy measurement of a poly(3-hexylthiophene) (P3HT) OTFT gated with a LiClO4:poly(ethyleneoxide) (PEO) dielectric. Based on spectroscopic signatures of molecular vibrations and polaron transitions,
we quantitatively determine charge carrier concentration and diffusion constants. We find two distinctively different regions:
at V
G≥−1.5 V, drift-diffusion (parallel to the semiconductor/dielectric interface) of hole-polarons in P3HT controls charging of
the device; at V
G<−1.5 V, electrochemical doping of the entire P3HT film occurs and charging is controlled by drift/diffusion (perpendicular
to the interface) of ClO4
− counter ions into the polymer semiconductor. 相似文献
7.
Here we report the synthesis, chemical stability, and electrical conductivity of Ti-doped perovskite-type BaCe0.8-x
Ti
x
Y0.2O3-δ
(x = 0.05, 0.1, 0.2, and 0.3; BCTY). Samples were synthesized by conventional solid state (ceramic) reaction from corresponding
metal salts and oxides at elevated temperature of 1,300–1,500 °C in air. The powder X-ray diffraction confirmed the formation
of a simple cubic perovskite-type structure with a lattice constant of a = 4.374(1), 4.377(1), and 4.332(1) ? for x = 0.05, 0.1, and 0.2 members of BCTY, respectively. Like BaCe0.8Y0.2O3-δ
(BCY), Ti substituted BCTY was found to be chemically not stable in 100% CO2 and form BaCO3 at elevated temperature. The bulk electrical conductivity of BCTY decreased with increasing Ti content and the x = 0.05 member exhibited the highest conductivity of 2.3 × 10−3 S cm−1 at 650 °C in air, while a slight increase in the conductivity, especially at low temperatures (below 600 °C), was observed
in humidified atmospheres. 相似文献
8.
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
9.
J. P. Xu X. Zou C. X. Li P. T. Lai C. L. Chan 《Applied Physics A: Materials Science & Processing》2009,94(2):419-422
Reactive cosputtering is employed to prepare high-permittivity HfTiO gate dielectric on n-Ge substrate. Effects of Ge-surface
pretreatment on the interface and gate leakage properties of the dielectric are investigated. Excellent performances of Al/HfTiO/GeO
x
N
y
/n-Ge MOS capacitor with wet–NO surface pretreatment have been achieved with a interface-state density of 2.1×1011 eV−1 cm−2, equivalent oxide charge of −7.67×1011 cm−2 and gate leakage current density of 4.97×10−5 A/cm2 at V
g
=1 V. 相似文献
10.
Aurélie Rolle Helen Seymour Pascal Roussel Annick Rubbens Rose-Noëlle Vannier 《Ionics》2008,14(6):477-482
The Ba2In2 − x
Sn
x
O5 + x/2 solid solution was confirmed up to x = 1 by solid-state reaction. X-ray diffraction at room and at elevated temperatures, Raman scattering and impedance spectroscopy
were used to characterise the samples. The structure refinement of the composition x = 0.1 from neutron diffraction data reveals that tin is preferentially located in the tetrahedral layers of the brownmillerite.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007 相似文献
11.
Xiangqian Shen Mingquan Liu Fuzhan Song Yongwei Zhu 《Applied Physics A: Materials Science & Processing》2011,104(1):109-116
Sr1−x
La
x
Zn
x
Fe12−x
O19/poly(vinylpyrrolidone) (PVP) (0.0≤x≤0.5) precursor nanofibers were prepared by the sol–gel assisted electrospinning method from starting reagents of metal salts
and PVP. Subsequently, the Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers with diameters of around 100 nm were obtained by calcination of the precursor at 800 to 1000°C for 2 h. The precursor
and resultant Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometer and
vibrating sample magnetometer. The grain sizes of Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers are in a nanoscale from 40 to 48 nm corresponding to the calcination temperature from 800 to 1000°C. With La–Zn
substitution content increase from 0 to 0.5, the grain size and lattice constants for the Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers obtained at 900°C show a steady reduction trend. With variations of the ferrite particle size arising from the
La–Zn substitution, the nanofiber morphology changes from the necklace-like structure linking by single elongated plate-like
particles to the structure building of multi-particles on the nanofiber cross-section. The specific saturation magnetization
of Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers initially increases with the La–Zn content, reaching a maximum value 72 A m2 kg−1 at x=0.2, and then decreases with a further La–Zn content increase up to x=0.5, while the coercivity exhibits a continuous reduction from 413 (x=0) to 219 kA m−1 (x=0.5). The mechanism for the La–Zn substitution and the nanofiber magnetic property are analyzed. 相似文献
12.
M. Bryushinin V. Golubev Y. Kumzerov D. Kurdyukov I. Sokolov 《Applied physics. B, Lasers and optics》2009,95(3):489-495
We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous
glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created
by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal
amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 (λ=442 nm, I
0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 (λ=532 nm, I
0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L
D=0.18 μm. 相似文献
13.
A series of (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+ (x=0.0–0.97, y=0.03) phosphors were synthesized by high-temperature solid-state reaction. The XRD patterns confirm the formation of a solid
solution of (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+. An intense tunable green light is observed with the increasing ratio of Sr/Ca. With an increase in x, the excitation and emission spectra show a redshift and blueshift, respectively, due to large centroid shift and small Stokes
shift. The temperature dependent luminescence is also investigated in the temperature range of 77–450 K. The Huang–Rhys factor
and the thermal-quenching temperature are determined. Intense green LEDs were successfully fabricated based on the (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+ phosphor and near-ultraviolet (∼395 nm) GaN/blue (460 nm) InGaN chips. All the results indicate that the solid solution (Ca1−x−y
Sr
x
)Si2O2N2:yEu2+ is a promising phosphor applicable to near-UV and blue LEDs for solid-state lighting. 相似文献
14.
The significance of heterovalent, substitutional disorder for the distribution of charge carriers in La2−x
Sr
x
CuO4 has been investigated. Disorder is shown to cause strong variations of binding energies of the ions ranging to some eV for
Sr contentsx=0.1. Balancing the energy for a hole transport, Cu3++O2−→Cu2++O−, and taking binding energy variations into account, the process is realized to become possible without consuming energy for
a subset Θ for allx Cu3+ in one formula unit of La2−x
Sr
x
CuO4. The functions Θ(x) are presented for hole transports to apex and in-plane oxygens, respectively. The delocalization of charge carriers is interpreted
to be caused by valency disorder on metal lattice sites. 相似文献
15.
W. J. Kossler X. H. Yu A. Greer H. E. Schone C. E. Stronach M. Davis R. S. Cary J. E. Crow W. F. Lankford J. Oostens 《Hyperfine Interactions》1991,63(1-4):81-86
Transverse and zero-field μSR measurements were made on YBa2(Cu1−xNix)3O7−y withx=0.1 and 0.2, and YBa2(Cu1−x
Zn
x
)3O7−y
withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence
was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained,
and the low temperature values of these are σ=3.2 μs−1.1.6μs−1, and 1 μs−1 forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs−1, 0.75 μs−1, 0.65 μs−1, and 0.4 μs−1 forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made,
but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction
in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the
relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect
of scattering. 相似文献
16.
LiAl
x
Mn2 − x
O4 and LiAl0.05Mn1.95O4 − y
F
y
spinel have been successfully synthesized by citric acid-assisted sol–gel method. The structure and physicochemical properties
of this as-prepared powder were investigated by electronic conductivity test, powder X-ray diffraction (XRD), scanning electron
microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test in detail. The electronic
conductivity decreases with increasing of the content of doped Al. XRD patterns show that the diffraction of LiAl0.05Mn1.95O4 − y
F
y
samples is similar, with all the peaks indexable in the Fd3m space group, and a little impurity appears in the LiAl0.05Mn1.95O3.8F0.2 sample. SEM reveals that all LiAl0.05Mn1.95O4 − y
F
y
powders have the uniform, nearly cubic structure morphology with narrow size distribution which is less than 500 nm. Galvanostatic
charge–discharge test indicates that LiAl0.05Mn1.95O4 has the highest discharge capacity and electrochemical performance among all LiAl
x
Mn2 − x
O4 samples after 50 cycles, and the initial discharge capacity of LiAl0.05Mn1.95O4 − y
F
y
(y = 0, 0.02, 0.05, 0.1) is 123.9, 124.6, 124.9, and 125.0 mAh g−1, respectively, and their capacity retention ratios are 94.2%, 94.9%, 91.7%, and 89.9% after 50 cycles, respectively. EIS
indicates that LiAl0.05Mn1.95O3.98F0.02 have smaller charge transfer resistance than that of LiAl0.05Mn1.95O4 corresponding to the extraction of Li+ ions. 相似文献
17.
The saccharide binding and conformational characterization of a hemagglutinin, a low molecular weight protein from the seeds
of Moringa oleifera was studied using steady state and time resolved fluorescence. The lectin binds sugars LacNAc (K
a = 1380 M−1) and fructose (K
a = 975 M−1), as determined by the fluorescence spectroscopy. It has a single tryptophan per monomer which is exposed on the surface
and is in a strong electropositive environment as revealed by quenching with iodide. Quenching of the fluorescence by acrylamide
involved both static (K
s = 0.216 M−1) and collisional (K
sv = 8.19 M−1) components. The native protein showed two different lifetimes, τ
1 (1.6 ns) and τ
2 (4.36 ns) which decrease and get converted into a single one, (2.21 ns) after quenching with 0.15 M acrylamide. The bimolecular
quenching constant, k
q
was 7.55 × 1011 M−1 s−1. ANS binding studies showed that the native protein has exposed hydrophobic patches which get further exposed at extreme
acidic or alkaline pH. However, they get buried in the interior of the protein in presence of 1 M GdnHCl or urea. 相似文献
18.
Poynor A. N. Cumblidge S. E. Rasera R. L. Catchen G. L. Motta A. T. 《Hyperfine Interactions》2001,136(3-8):549-553
We have measured nuclear electric–quadrupole interactions (EQI) at 181Ta impurities substituted as Hf atoms into the Zr site in Zr2Ni. Using perturbed-angular-correlation (PAC) spectroscopy, we measured the EQI over temperatures ranging from 10 to 1200
K. Over the entire range of temperature, the Zr2Ni crystal has a bct Al2Cu structure that includes a single Zr site. The crystal field symmetry surrounding this site is rather low, giving rise to
a highly asymmetric electric-field gradient tensor. At 10 K, the EQI is characterized by an angular frequency ω0=601(3) Mrad s−1, and an asymmetry parameter η=0.835(2). At 1200 K, ω0 decreases to 516(3) Mrad s−1, and η also decreases to 0.790(4). Although weak, the temperature dependence of ω0 is consistent with a (1−BT
3/2) power law, in which B=6×10−6 K−3/2. The EQI also manifests a very narrow linewidth. We observed no evidence either for magnetic ordering or for structural phase
transitions in the temperature range covered by this experiment. Moreover, the sharpness of the EQI indicates that the samples
as prepared are remarkably free of strain and defects. These results indicate that the Zr2Ni structure does not promote the formation of defects and that the power-law dependence of ω0 on T is insensitive to the asymmetric nature of the crystal.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
19.
This paper is contributed to explore all possible single peakon solutions for the Degasperis–Procesi (DP) equation m
t
+ m
x
u + 3mu
x
= 0, m = u − u
xx
. Our procedure shows that the DP equation either has cusp soliton and smooth soliton solutions only under the inhomogeneous boundary condition lim|x|→ ∞
u =A ≠0, or possesses the regular peakon solutions ce
− |x − ct| ∈ H
1 (c is the wave speed) only when lim|x|→ ∞
u = 0 (see Theorem 4.1). In particular, we first time obtain the stationary cuspon solution of the DP equation. Moreover we present new cusp solitons (in the space of ) and smooth soliton solutions in an explicit form. Asymptotic analysis and numerical simulations are provided for smooth
solitons and cusp solitons of the DP equation.
相似文献
20.
Bi4V2O11 exists in three phases viz. α, β, and γ. High temperature γ-phase can be stabilized to room temperature owing to its higher
conductivity by the partial substitution of metallic cations for vanadium in Bi4V2O11. Phase transitions from α → β and β → γ are composition and temperature-dependent. Mn2+-doped compounds Bi4V2−x
Mn
x
O11−
δ
(0 ≤ x ≤ 0.4) have been synthesized by solid state reaction technique and investigated by X-ray diffraction and ionic conductivity
measurement. High ionic conducting γ-phase is stabilized for x ≥ 0.2. The ionic conductivity of the series of Bi4V2−x
Mn
x
O11−
δ
samples has been measured by using ac impedance spectroscopy technique. The conductivity data do show departure from its
simple Arrhenius behavior for all of the compositions. The highest conductivity observed for x = 0.2 sample can be attributed to lower activation energy. 相似文献