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31.
D. Mikhailova H. Ehrenberg D. Trots G. Brey H. Fuess 《Journal of solid state chemistry》2009,182(6):1506-951
Mixed chromium-rhenium oxides, CrxRe1−xO2 with 0.31?x?0.66, have been synthesized for the first time by high-pressure high-temperature synthesis and in evacuated quartz tubes. The crystal structures of the compounds have been determined by single crystal and powder X-ray diffraction. Depending on synthesis conditions (pressure and temperature) these phases crystallize either in a tetragonal structure (P42/mnm) with statistical distribution of metal ions on one site (rutile-type), with cation ordering along c-axis (trirutile-type), or in a monoclinic rutile-like structure (C2/m) with ordering of Cr- and Re-cations and metallic Re-Re bonds. The “a” parameter of the tetragonal unit cell increases with increasing Re content whereas the “c” parameter decreases, indicating a strengthening of the Re-Re bond. The thermal stability of tetragonal CrxRe1−xO2 in Ar-atmosphere depends on the Re-content, decomposition is observed at 1241 K for x=0.34, but already at 966 K for x=0.5. The thermal expansion of CrxRe1−xO2 is anisotropic with a larger expansion coefficient in the “c” direction. Tetragonal CrxRe1−xO2 with 0.31?x<0.54 order antiferromagnetically at low temperatures with TN depending on the Cr-content x. 相似文献
32.
Angelina Sarapulova Daria Mikhailova Ljubomira Ana Schmitt Steffen Oswald Natalia Bramnik Helmut Ehrenberg 《Journal of Sol-Gel Science and Technology》2012,62(1):98-110
LiCoPO4-coated disordered carbon nanofibers (CNFs/LiCoPO4) were obtained by a sol–gel method, using triethyl phosphite or triethyl phosphate as the phosphorous source. The crystal
structure of the products was analyzed by X-ray powder diffraction, while morphology was studied using scanning electron microscopy,
transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. Optimal synthesis conditions
for the CNFs/LiCoPO4 in light of the best electrochemical performance are discussed. The best discharge capacity 105 mAh/g (or ca. 63% of the
theoretical capacity) shows the material with 40% CNFs/LiCoPO4 and addition coating by carbon black. This composition has a best purity of active materials and point coverage of CNFs.
The X-ray photoelectron C1s spectra of the CNFs surface without and with sputter erosion show enhancement of C–O bonds at
the fiber surface, which does not influence significantly electrochemical behavior of the composite materials. 相似文献
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34.
V.V. Pavlyuk G.S. Dmytriv I.I. Tarasiuk I.V. Chumak H. Pauly H. Ehrenberg 《Solid State Sciences》2010,12(2):274-280
A phase transition from the cubic CsCl-type structure (Pm-3m space group) into a tetragonal UPb-type structure (I41/amd) is observed for the LiAg binary compound at ambient conditions. The crystal structure of the tetragonal modification of the LiAg binary compound was solved by direct methods in SHELXS on the base of structure factors which were extracted from a powder diffraction pattern and refined by SHELXL and the Rietveld method (a = 3.9605(1), c = 8.2825(2) Å, Bragg R-factor = 4.81, Rf-factor = 4.87). Elevated temperatures and/or a small Li-excess versus the equimolar composition favour the cubic structure whereas ambient and lower temperatures and/or a small Li-deficiency stabilize the tetragonal structure. This reconstructive transition is reversible but proceeds slowly. 相似文献
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38.
Ahmed M. Hashem Ashraf E. Abdel Ghany Kristian Nikolowski Helmut Ehrenberg 《Ionics》2010,16(4):305-310
LiNi0.5Mn0.5O2 powder was synthesized by a coprecipitation method. LiOH.H2O and coprecipitated [(Ni0.5Mn0.5)C2O4] precursors were mixed carefully together and then calcined at 900°C. Surface modified cathode materials were obtained by
coating LiNi0.5Mn0.5O2 with a thin layer of amorphous carbon using table sugar and starch as carbon source. Both parent and carbon-coated samples
have the characteristic layered structure of LiNi0.5Mn0.5O2 as estimated from X-ray diffractometry measurements. Transmission electron microscope showed the presence of C layer around
the prepared particles. TGA analysis emphasized and confirmed the presence of C coating around LiNi0.5Mn0.5O2. It is obvious that the carbon coating appears to be beneficial for the electrochemical performance of the LiNi0.5Mn0.5O2. A capacity of about 150 mAh/g is delivered in the voltage range 2.5–4.5 V at current density C/15 for carbon coated LiNi0.5Mn0.5O2 in comparison with about 165 mAh/g obtained for carbon free LiNi0.5Mn0.5O2 at the same current density and voltage window. About 92% and 82% capacity retention was obtained at 50th cycle for coated
LiNi0.5Mn0.5O2 using sucrose and starch, respectively; whereas, 75% was retained after only 30th cycle for carbon free LiNi0.5Mn0.5O2. This improvement is mainly attributed to the presence of thin layer of carbon layer that encapsulate the nanoparticles and
improve the conductivity and the electrochemical performance of LiNi0.5Mn0.5O2. 相似文献
39.
L. Balsanova D. Mikhailova A. Senyshyn D. Trots H. Fuess W. Lottermoser H. Ehrenberg 《Solid State Sciences》2009,11(6):1137-1143
Silver diiron tris(oxomolybdate), α-AgFe2(MoO4)3, was synthesized in sealed silica tubes at 1050 K and is isostructural to α-NaFe2(MoO4)3, determined by single-crystal X-ray diffraction (space group P?1, a = 6.9320(7) Å, b = 6.9266(6) Å, c = 10.9732(13) Å, α = 81.197(8)°, β = 83.456(9)°, γ = 81.352(8)° at 300 K, Z = 2). The crystal structure is built up from both monomers and edge-sharing dimers of [FeO6]-octahedra, which are linked with each other by isolated [MoO4]-tetrahedra to a three-dimensional network. Ag ions are situated on a site with four near oxygen neighbours. Thermal expansion is most pronounced along the c-axis, while the angle α decreases with increasing temperature. Antiferromagnetic ordering is indicated by a sharp maximum in the temperature dependence of magnetization at 21.5(5) K, and a magnetic moment of 5.36(1) μB per Fe-ion was derived from the Curie constant in the paramagnetic region. The collinear antiferromagnetic structure with propagation vector k = (0,½,½) and an ordered magnetic moment of 4.62(9) μB per Fe-ion were deduced from neutron powder diffraction data and give evidence for an underlying magnetic interaction mechanism, resulting in rather strong and long-ranged couplings. Mössbauer spectroscopy shows a change in the electronic configuration on the two distinct Fe sites between room temperature and 150 K, accompanied by an increase of the average Fe–O distance for one site and a shrinking one for the other as expected for charge ordering in a mixed valence compound with Fe(II) and Fe(III). 相似文献
40.
Natalia V. Kuratieva Daria Mikhailova Helmut Ehrenberg 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(11):i85-i86
A new polymorph of nonacopper(II) bis(orthoborate) bis(hexaoxodiborate), Cu9(BO3)2(B2O6)2, or Cu3B2O6 with Z′ = 3, has a pseudo‐layered monoclinic structure containing BO3 triangles and B2O6 units consisting of corner‐sharing BO3 triangles and BO4 tetrahedra. The compound was obtained during an investigation of the Li–Cu–B–O system. In contrast to the triclinic form of Cu3B2O6, the layers are linked to one another by BO4 tetrahedra. 相似文献