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1.
We report the generation of efficient white light based on upconversion (UC) in Tm3+/Er3+/Yb3+:Y2O3 nanocrystalline phosphor synthesized by simple and cost effective solution combustion technique on 976 nm laser excitation.
The calculated color coordinates (using 1931 CIE standard) for samples annealed at different temperatures vary from (0.16,
0.30) to (0.32, 0.33) with dopant concentration, annealing temperature and the pump power; thus providing a wide color tunability
including the white one. White emission is observed even at a very low laser power (60 mW). The maximum upconversion efficiency
obtained for white emission is 2.79% with the color coordinates (0.30, 0.32) at laser power of 420 mW which is quite close
to the standard white color coordinates. 相似文献
2.
Li4Ti5O12/Cu2O composite was prepared by ball milling Li4Ti5O12 and Cu2O with further heat treatment. The structure and electrochemical performance of the composite were investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Li4Ti5O12/Cu2O composite exhibited much better rate capability and capacity performance than pristine Li4Ti5O12. The discharge capacity of the composite at 2 C rate reached up to 122.4 mAh g?1 after 300 cycles with capacity retention of 91.3 %, which was significantly higher than that of the pristine Li4Ti5O12 (89.6 mAh g?1). The improvement can be ascribed to the Cu2O modification. In addition, Cu2O modification plays an important role in reducing the total resistance of the cell, which has been demonstrated by the electrochemical impedance spectroscopy analysis. 相似文献
3.
In order to improve the rate capability of Li4Ti5O12, Ti4O7 powder was successfully fabricated by improved hydrogen reduction method, then a dual-phase composite Li4Ti5O12/Ti4O7 has been synthesized as anode material for lithium-ion batteries. It is found that the Li4Ti5O12/Ti4O7 composite shows higher reversible capacity and better rate capability compared to Li4Ti5O12. According to the charge-discharge tests, the Li4Ti5O12/Ti4O7 composite exhibits excellent rate capability of 172.3 mAh g?1 at 0.2 C, which is close to the theoretical value of the spinel Li4Ti5O12. More impressively, the reversible capacity of Li4Ti5O12/Ti4O7 composite is 103.1 mAh g?1 at the current density of 20 C after 100th cycles, and it maintains 84.8% of the initial discharge capacity, whereas that of the bare spinel Li4Ti5O12 is only 22.3 mAh g?1 with a capacity retention of 31.1%. The results indicate that Li4Ti5O12/Ti4O7 composite could be a promising anode material with relative high capacity and good rate capability for lithium-ion batteries. 相似文献
4.
D. Do S. S. Kim S. W. Yi J. W. Kim 《Applied Physics A: Materials Science & Processing》2009,94(3):697-701
Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi4Ti4O15 grown on Bi4Ti3O12, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared
on a Pt(111)/Ti/SiO2/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin
films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P
r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm2 at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 1010 switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi4Ti4O15 on Bi4Ti3O12 ferroelectric thin films were better than those of the SrBi4Ti4O15 grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth
kinetics of SrBi4Ti4O15 on the c-axis-oriented Bi4Ti3O12 layer or on the Pt-coated Si substrate. 相似文献
5.
Tingyin Ning Cong Chen Yueliang Zhou Heng Lu Dongxiang Zhang Hai Ming Guozhen Yang 《Applied Physics A: Materials Science & Processing》2009,94(3):567-570
CaCu3Ti4O12 (CCTO) thin films were successfully prepared on LaAlO3 substrates by pulsed laser deposition technique. We measured the nonlinear optical susceptibility of the thin films using
Z-scan method at a wavelength of 532 nm with pulse durations of 25 ps and 7 ns. The large values of the third-order nonlinear
optical susceptibility, χ
(3), of the CCTO film were obtained to be 2.79×10−8 esu and 3.30×10−6 esu in picosecond and nanosecond time regimes, respectively, which are among the best results of some representative nonlinear
optical materials. The origin of optical nonlinearity of CCTO films was discussed. The results indicate that the CCTO films
on LaAlO3 substrates are promising candidate materials for applications in nonlinear optical devices. 相似文献
6.
A. N. Georgobiani V. B. Gutan O. Ya. Manashirov 《Bulletin of the Lebedev Physics Institute》2010,37(10):304-308
The ranges of the existence of solid solutions in binary systems Ln2O2S-Yb2O2S(Ln = Y, La, Gd) were found and main features of variations of Stokes IR luminescence intensity of Ln2O2S·Yb in the range of 0.96–1.1 μm were determined depending on the composition during IR excitation. Based on the established
features, a new Y2O2S:Yb monospectral IR phosphor was developed, which, upon excitation by a 0.940-μm laser, is characterized by an increased
Stokes IR luminescence intensity in the range of 0.96–1.1 μm in comparison with that of known commercial phosphor. 相似文献
7.
Jungang Hou R. V. Kumar Yuanfang Qu Dalibor Krsmanovic 《Journal of nanoparticle research》2010,12(2):563-571
Bi4Ti3O12 (BIT) nanoparticles with a narrow average particle size distribution in the range of 11–46 nm was synthesized via a metal-organic polymeric precursor process. The crystallite size and lattice parameter of BIT were determined by XRD analysis. At annealing temperatures >550 °C, the orthorhombic BIT compound with lattice parameters a = 5.4489 Å, b = 5.4147 Å, and c = 32.8362 Å was formed while at lower annealing temperatures orthorhombicity was absent. Reaction proceeded via the formation of an intermediate phase at 500 °C with a stoichiometry close to Bi2Ti2O7. The particle size and the agglomerates of the primary particles have been confirmed by FESEM and TEM. The decomposition of the polymeric gel was ascertained in order to evaluate the crystallization process from TG-DSC analysis. Raman spectroscopy was used to investigate the lattice dynamics in BIT nanoparticles. In addition, investigation of the dependence of the visible emission band around the blue–green color emission on annealing temperatures and grain sizes showed that the effect of grain size plays important roles, and that oxygen vacancies may act as the radiative centers responsible for the observed visible emission band. 相似文献
8.
N. A. Zhuravlev N. A. Mukhina D. G. Kellerman V. S. Gorshkov 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(11):1522-1524
The processes of lithium redistribution in the structure of cubic Li4Ti5O12 spinel, caused by both chromium doping and thermal activation, have been investigated by nuclear magnetic resonance. It is
shown that Li ions migrate from tetra- to octahedral crystallographic positions with an increase in temperature. This process
becomes more pronounced at temperatures above 400 K. In contrast, the fraction of tetrahedrally coordinated Li increases as
a result of doping with chromium. 相似文献
9.
Mohammad Asadikiya Yuexing Zhu Srikanth Gopalan Yu-cheng Chuang Ping-chun Tsai Ralph Nicolai Nasara Shih-kang Lin Yu Zhong 《Ionics》2018,24(3):707-713
The Li4Ti5O12 is applied in lithium ion batteries as anode material, which can be synthesized by various synthesis techniques. In this study, the molten salt synthesis technique at low temperatures, i.e. 350 °C, was applied to synthesize Li4Ti5O12. Surprisingly, the Li4Ti5O12 was not formed according to XRD analysis, which raised question about the stability range of Li4Ti5O12. To investigate the stability of Li4Ti5O12 at low temperatures, the high-temperature calcined Li4Ti5O12 powder was equilibrated in the LiCl-KCl eutectic salt at 350 °C. The result of experiment revealed that the Li4Ti5O12 is not decomposed. Results of ab initio calculations also indicated that the Li4Ti5O12 phase is a stable phase at 0 K. The products of molten salt synthesis technique were then annealed at 900 °C, which resulted in the Li4Ti5O12 formation. It was concluded that the Li4Ti5O12 is a stable phase at low temperatures and the reasons for not forming the Li4Ti5O12 by molten salt technique at low temperature are possibly related to activation energy and kinetic barriers. The Li4Ti5O12 formation energy is also very small, due to the results of ab initio calculations. 相似文献
10.
Ruiting Sun Xiaoli Wang Jing Shi Le Wang 《Applied Physics A: Materials Science & Processing》2011,104(1):129-133
New perovskite solid solution ceramics of (1−x)BaTiO3-xBi(Mg1/2Ti1/2)O3 ((1−x)BT-xBMT, x≤0.09) were synthesized by the solid-state reaction technique. X-ray diffraction studies have revealed a stable single perovskite
structure for all samples. Dielectric measurements were carried out at different frequencies and temperatures. The polarization
evolutions with temperatures were measured to investigate the ferroelectric properties. All the compositions show features
of ferroelectrics with diffuse phase transition, though the temperature T
m
of their dielectric constant maximum ε
m
is frequency dependent. The dielectric constant peak ε(T) of (1−x)BT-xBMT ceramics become broad with increasing BMT content. During the temperature range of ε(T) peak summit, (1−x)BT-xBMT ceramics present quasi-linear dielectric phenomenon under high electric field with very high dielectric constant. 相似文献
11.
Jungang Hou Yuanfang Qu Dalibor Krsmanovic R. V. Kumar 《Journal of nanoparticle research》2010,12(5):1797-1805
Well-dispersed bismuth titanate (BIT) nanocrystals with an average size ranged from 3 to 60 nm were synthesized via a peroxide-based
route assisted with an inverse microemulsion process. The crystallite size and lattice parameter of BIT upon variable-temperature
were determined by X-ray diffraction (XRD). The particle size was confirmed by transmission electron microscopy (TEM). Thermal
decomposition behaviour of Ti-peroxy and BIT gel and crystallization kinetics of BIT nanocrystals were investigated by differential
scanning calorimetry/thermogravimetry (DSC/TG) and Fourier-Transform infrared spectroscopy (FTIR). Analysis of nonisothermal
DSC data yielded a value of 220.84 ± 2.73 KJ/mol and 2.25 ± 0.26 for the activation energy of crystallization (E
a) and the Avrami exponent (n), respectively. 相似文献
12.
Influence of an external magnetic field on the reluctance of the YBa
2
Cu
3
O
x ceramics is investigated. A significant reluctance of the oxygen-deficient ceramics (with critical temperature Tc < 77 K) is established for a sample in the normal state at T < 160 K. It is demonstrated that after ceramics annealing that
restores the oxygen content to a nearly optimum value, the magnetic field has essentially no effect on the sample reluctance
at temperatures exceeding Tc. To explain the revealed mechanisms, a model involving ferromagnetic clusters effectively decreasing the free carrier density
is used.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 68–71, April, 2007. 相似文献
13.
AC impedance spectroscopy technique has been used to study electrical properties of Bi3.25La0.75Ti3O12 (BLT) ceramic. Complex impedance plots were fitted with three depressed semicircles, which are attributed to crystalline
layer, plate boundary and grain boundary and all three were found to comprise of universal capacitance nature [C = C0w
n−1]. Grain boundary resistance and capacitance evaluated from complex impedance plots have larger values than that of plate
boundary and crystalline layer. The activation energies (E
a) for DC-conductance in grain boundary, plate boundary and crystalline layer are 0.68 eV, 0.89 eV and 0.89 eV, respectively.
Relaxation activation energies calculated from impedance plots showed similar values, 0.81 eV and 0.80 eV for crystalline
layer and plate boundary, respectively. These activation energy values are found to be consistent with the E
a value of oxygen vacancies in perovskite materials. A mechanism is offered to explain the generation of oxygen vacancies in
BLT ceramic and its role in temperature dependence of DC-conductance study.
相似文献
14.
Jian-Ping Zhou Hong-Cai He Yi Zhang Chao-Yong Deng Zhan Shi Ce-Wen Nan 《Applied Physics A: Materials Science & Processing》2007,89(2):553-558
CoFe2O4 (CFO) thin film with highly (111)-preferential orientation was first deposited on the silicon substrate by a pulsed-laser
deposition, and then Pb(Zr0.52Ti0.48)O3 (PZT) layers were deposited with different oxygen pressures to form the bilayer CFO/PZT nanocomposite thin films. X-ray diffraction
showed that the PZT preferential orientation was strongly dependant on the oxygen pressure. The smooth film surface was obtained
after depositing the CFO and PZT layers. The bilayer thin films exhibit good ferromagnetic and ferroelectric properties, and
a low leakage current density of 0.004 μA/cm2 at 50 kV/cm. The leakage current density curves show loops for the electric polarized field when the electric field reverses.
PACS 77.84.Lf; 75.80+q; 81.05.Zx; 81.15.Fg 相似文献
15.
S/Li4Ti5O12 cathode with high lithium ionic conductivity was prepared for Li-S battery. Herein, nano Li4Ti5O12 is used as sulfur host and fast Li+ conductor, which can adsorb effectively polysulfides and improve remarkably Li+ diffusion coefficient in sulfur cathode. At 0.5 C, S/Li4Ti5O12 cathode has a stable discharge capacity of 616 mAh g?1 at the 700th cycle and a capacity loss per cycle of 0.0196% from the second to the 700th cycle, but the corresponding values of S/C cathode are 437 mAh g?1 and 0.0598%. Even at 2 C, the capacity loss per cycle of S/Li4Ti5O12 cathode is only 0.0273% from the second to the 700th cycle. The results indicate that Li4Ti5O12 as the sulfur host plays a key role on the high performance of Li-S battery due to reducing the shuttle effect and enhancing lithium ionic conductivity. 相似文献
16.
L. S. Kamzina I. P. Raevskii S. M. Emel’yanov S. I. Raevskaya E. V. Sahkar 《Physics of the Solid State》2004,46(5):908-914
The dielectric and optical (optical transmission, small-angle light scattering, birefringence) properties of PMNT-0.2 single crystals and their variation induced by a dc electric field have been studied. The birefringence was found to increase anomalously at the transition from the rhombohedral ferroelectric to the inhomogeneous relaxor phase (the spontaneous ferroelectric transition temperature Tsp). Below Tsp, the dielectric and optical properties were observed to exhibit anomalies originating from reorientation and growth of domains in size. Unlike ferroelectric relaxors of the type of PbB′1/3B′2/3O3 and PbB′1/2B′1/2O3, in PMNT-0.2 neither induction of the ferroelectric phase by an electric field nor thermally stimulated destruction of the ferroelectric state occurs through the percolation mechanism (i.e., they are not accompanied by anomalously narrow maxima in small-angle light scattering). This is attributed to the inhomogeneous structure of the relaxor phase, as a result of which the phase transition does not take place simultaneously in various regions of the crystal. 相似文献
17.
A Cu2+-doped single crystal of catena-trans-bis(N-(2-hydroxyethyl)-ethylenediamine) zinc(II)-tetra-m-cyanopaladate(II) [ZnPd(CN)4(C4H12N2O2)] complex has been investigated by electron paramagnetic resonance (EPR) technique at room temperature. EPR spectra indicate
that Cu2+ ions substitute for magnetically equivalent Zn2+ ions and form octahedral complexes in [ZnPd(CN)4(C4H12N2O2)] hosts. The crystal field affecting the Cu2+ ion is nearly axial. The optical absorption studies show two bands at 322 nm (30864 cm−1) and 634 nm (15337 cm−1) which confirm the axial symmetry. The spin Hamiltonian parameters and the relevant wave function are determined. 相似文献
18.
Li4Ti5O12 is regarded as the ideal anode material for its stable structure, high charge/discharge platform, and safety performance. But low ionic and electronic conductivity of the Li4Ti5O12 anode material under the condition of low temperature greatly limit its application in practical production. In this paper, some modified methods for improving the low-temperature electrochemical performance of Li4Ti5O12 anode material were summarized. Meanwhile, we explored its influence mechanisms at low temperature, one is, with the subtle changes of lattice parameters and oxygen atom fraction coordinates of Li4Ti5O12 at low temperature, the changes of the bond length influence the structural stability of Li4Ti5O12 and the diffusion path of lithium ions; the other reason is that the charge transfer resistance increases obviously and the lithium ion diffusion coefficient reduces under low temperature. Finally, the research directions for improving the low-temperature electrochemical performance were proposed. 相似文献
19.
Manglesh Dixit Shovit Bhattacharya Rajneesh Mohan Kiran Singh P. S. R. Krishna Vilas Shelke N. K. Gaur R. K. Singh 《Pramana》2004,63(2):233-237
The HgO-added YBa2Cu3O7−δ (YBCO) superconductor has been studied for its structural and superconducting properties. Polycrystalline YBCO samples were
synthesized through solid-state reaction method by adding HgO in different concentrations without using oxygen annealing.
All the samples showed a sharp superconducting transition temperature around 90 K. The X-ray diffraction patterns of all the
samples revealed monophasic Y-123 nature. The structural studies were carried out by neutron scattering and Rietveld analysis.
The neutron scattering revealed that Hg is not incorporated in the Y-123 system and has shown optimum oxygen concentration.
The significant role played by the HgO is to provide oxygen ambient through its decomposition, thus changing the oxygen balance
in favour of high Cu-valence state. 相似文献
20.
Highly c-axis-oriented Sr3Bi4Ti6O21 (SBTi) thin films were fabricated on Pt-coated Si substrates by pulsed laser deposition (PLD). The structures were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). No peaks of SrTiO3 (STO) could be detected in the XRD pattern, indicating the existence of the SBTi single phase. Good ferroelectric hysteresis loops of the films with Pt electrodes were obtained. With an applied field of 400 kV/cm, the measured remanent polarization (Pr) and coercive field (Ec) values were 4.1 C/cm2 and 75 kV/cm respectively. The films showed little fatigue after 2.22×109 switching cycles: the nonvolatile polarizations decreased by less than 5% of the initial values. The dielectric constant and the loss tangent of the films were measured to be 363 and 0.04 at 100 kHz. These results might be advantageous for nonvolatile ferroelectric random access memory (NVFRAM) and dynamic random access memory (DRAM). PACS 77.84.Dy; 77.22.-d; 68.55.Jk 相似文献