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121.
122.
Spectroscopic determination of the cross-membrane electric potential has been used for more than 20 years. This method, which usually employs absorption or fluorescence measurements, allows for a rapid and noninvasive study of the electrical properties of the membranes of cells and liposomes. However, the usual fluorescence techniques preferably allow monitoring changes in the potential on triggerable or excitable membranes, and not the absolute value of the potential. They also do not provide means for measuring the potential on single cells. This paper reviews three methods that solve these issues. Nernstian dyes which partition between intra-and extracompartmental volumes enable a fluorescence microscopic determination of a single cell and even a single organelle. Dual-wavelength ratiometric recording from membrane-staining dyes also provides means for measuring the field on a single cell. Resonance Raman probes provide a spectroscopic method with a natural internal standard for the absolute measurement of membrane potential. 相似文献
123.
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125.
The lithium double diphosphates LiCryFe1−yP2O7 have been investigated by X-ray diffraction, SQUID measurements and vibrational spectroscopy. The Rietveld refinements based on the XRD patterns show the existence of a continuous solid solution over the whole composition range (0?y?1.0) with a continuous evolution of the monoclinic unit cell parameters (S.G. P21). The transition metal ions connect the diphosphate anions forming a three-dimensional network with channels filled by Li+ cations expected to exhibit high mobility. All compounds order magnetically at low temperatures due the Fe-Fe interactions. The ordering temperature decreases with increasing Cr content. The slope in Curie-Weiss fits to the 1/χ vs T data in the paramagnetic domain clearly shows the existence of Fe3+ and Cr3+ in their high spin states, and a ferromagnetic component is clearly detected for y=0, 0.2 and 0.4. IR spectra have been interpreted using factor group analysis. The small shift of the frequencies is due to the influence of the chromium amount. The POP angles were estimated using the Lazarev's relationship. 相似文献
126.
Y.J. Wei K. Nikolowski S.Y. Zhan H. Ehrenberg S. Oswald G. Chen C.Z. Wang H. Chen 《Electrochemistry communications》2009,11(10):2008-2011
Li[Li0.23Co0.3Mn0.47]O2 cathode material was prepared by a sol–gel method. The material had a primary particle size of about 100 nm, covered by a 30 Å of Li2CO3 layer. The material showed promising electrochemical performance when cycled up to 3C rate. The electrochemical kinetics of the first charge was much slower than that of the second charge, due to the complex electrochemical process which involved not only Li+ diffusion but also release of oxygen. By taking account of this, the material was pre-charged very slowly (C/50) in the first cycle. This led to excellent electrochemical performance in the following cycles. For instance, the 1C-rate capacity increased to 168 mA h g−1 after 50 cycles, comparing with the 145 mA h g−1 obtained without pre-charging. 相似文献
127.
Helmut Ehrenberg Natalia N. Bramnik Anatoliy Senyshyn Hartmut Fuess 《Solid State Sciences》2009,11(1):18-23
Precise structural data have been determined from a combined Rietveld refinement, based on neutron and X-ray powder diffraction data simultaneously, for the three phases LiCoPO4, LizCoPO4 with a specific intermediate Li-content z = 0.60(10) and CoPO4, which are obtained by electrochemical Li-extraction from LiCoPO4. All three phases are isopointal. Therefore, the transitions between these phases are necessarily of first order, in agreement with their observed coexistence. The same collinear antiferromagnetic structures with magnetic moments nearly parallel to the [010] direction are observed for LiCoPO4 and LizCoPO4, but with a significantly higher Néel temperature of 76 K for the latter compound in comparison with 23 K for LiCoPO4. Olivine-type CoPO4 can only be prepared from LiCoPO4 by delithiation and its physical properties were investigated for the first time. An antiferromagnetic arrangement along the [100] direction is observed for CoPO4 with an additional weak ferromagnetic component along the [001] direction (magnetic space group Pn′m′a and TC = 45 K). The magnetic moment of 3.1(2) μB per Co-ion indicates a mainly high-spin state for Co3+ in the octahedral coordination of CoPO4, which is exceptional and probably the first example in a phosphate. The easy axes and the magnetic exchange interactions between Co-ions change dramatically with the Co2+ ? Co3+ transition. A continuous change of the formal oxidation state of a transition element by electrochemical Li-extraction and a quasi-continuous in situ observation of the resulting magnetic structure by neutron diffraction appear feasible. 相似文献
128.
New concepts for Li-ion batteries are of growing interest for high-performance applications. One aim is the search for new
electrode materials with superior properties and their detailed characterization. We demonstrate the application of X-ray
photoelectron spectroscopy (XPS) to investigate electrode materials (LiCoO2, LiCrMnO4) during electrochemical cycling. The optimization of a “quasi in situ” analysis, by transferring the samples with a transport
chamber from the glove box to the XPS chamber, and the reliability of the experiments performed are shown. The behavior of
characteristic chemical species at the electrodes and the changes in oxidation states of LiCrMnO4 during cycling is discussed. The formation of Cr6+ is suspected as a possible reason for irreversible capacity loss during charging up to complete Li deintercalation (approximately
5.2 V).
Figure Scheme of a quasi in situ XPS experiment on Li-ion battery electrode material 相似文献
129.
S.Y. Zhan C.Z. Wang K. Nikolowski H. Ehrenberg G. Chen Y.J. Wei 《Solid State Ionics》2009,180(20-22):1198-1203
Cr0.1V2O5.15 was prepared by an oxalic acid assisted sol–gel method. X-ray diffraction showed that Cr doping induced a slight expansion (ΔV/V ≈ 2.3%) in the crystal lattice of V2O5. The electrochemical properties of Cr0.1V2O5.15 in the potential range of 3.8–2.0 V were studied by cyclic voltammetry, galvanostatic charge–discharge cycling and potentiostatic intermittent titration technique. Cyclic voltammetry showed that the irreversible phase transition of V2O5 during the first cycle was effectively prevented by Cr doping. This caused the good charge–discharge cycling performance of the doped material. The discharge capacities were recorded to be 200, 170 and 120 mAhg− 1 after fifty cycles at the C/10, C/2 and 1C rates, respectively. However, ex-situ X-ray diffraction showed that the crystal structure of the material was destroyed after long-term cycling. The lithium diffusion coefficient of Cr0.1V2O5.15 varied between 10− 11 and 10− 12 cm2 s− 1, which was larger than that of crystalline V2O5, and was close to those of metal doped V2O5 in previous reports. The improvement in lithium diffusion kinetics was regarded as an important reason for the good electrochemical performance of Cr0.1V2O5.15. 相似文献
130.
S. S. El-Deen A. M. Hashem A. E. Abdel Ghany S. Indris H. Ehrenberg A. Mauger C. M. Julien 《Ionics》2018,24(10):2925-2934
Anatase TiO2 nanoparticles were prepared by a simple sol-gel method at moderate temperature. X-ray powder diffraction (XRD) and Raman spectroscopy revealed the exclusive presence of anatase TiO2 without impurities such as rutile or brookite TiO2. Thermogravimetric analysis confirmed the formation of TiO2 at about 400 °C. Particle size of about 20 nm observed by transmission electron microscopy matches well with the dimension of crystallites calculated from XRD. The electrochemical tests of the sol-gel-prepared anatase TiO2 show promising results as electrode for lithium-ion batteries with a stable specific capacity of 174 mAh g?1 after 30 cycles at C/10 rate. The results show that improvement of the electrochemical properties of TiO2 to reach the performance required for use as an electrode for lithium-ion batteries requires not only nanosized porous particles but also a morphology that prevents the self-aggregation of the particles during cycling. 相似文献