The products of decomposition of manganese carbonate with and without doping by copper or cobalt, at temperatures ,500 uC in air were studied. Doped systems with 20 atom% Cu or Co give new nanometric manganese oxides agglomerated in submicronic spheres at 370 uC. Transmission electron microscopy (TEM) shows that these X-ray amorphous compounds are nanocrystalline with grain size in the 10 nm range and a spinel substructure. The electrochemical behaviour of these materials in lithium cells was studied. Whereas non-doped manganese oxide exhibits poor intercalation capabilities, the freshly co-precipitated Cu or Co doped materials can be cycled successfully around 3 V vs. Li/Li + . Step-potential electrochemical spectroscopy shows that the initial discharge gives rise to a two-phase transition and is followed by stable, reversible, singlephase cycling. Best results are obtained on a cobalt-doped manganese oxide (Co : Mn 5 1 : 5), which can sustain more than 100 charge-discharge cycles with a 175 mA h g 21 capacity in the 1.8-4.2 V range. XAS spectra were measured on pristine and electrochemically discharged materials, showing that (1) in the cobalt-doped material, cobalt is divalent and manganese is the only redox-active species, (2) the variations in local structure around Mn on discharge are much smaller than in long-range ordered compounds such as Li-Mn-O spinels.
Articles you may be interested inEffects of magnetic flux density and substrate bias voltage on Ni films prepared on a flexible substrate material using unbalanced magnetron sputtering assisted by inductively coupled plasma J. Vac. Sci. Technol. A 32, 02B104 (2014); 10.1116/1.4832226Copper enhanced (111) texture in silver thin films on amorphous Si O 2 Low temperature plasma-assisted chemical vapor deposition of tantalum nitride from tantalum pentabromide for copper metallization Pure copper films have been deposited by microwave plasma-assisted sputtering on ͑100͒-oriented single crystal silicon substrates mounted on a water-cooled substrate holder either maintained at the floating potential or biased to various dc voltages ranging from 0 to Ϫ125 V. The argon pressure was fixed at 0.13 Pa and argon ions from the discharge produced in a distributed electron cyclotron resonance microwave plasma chamber were used for sputtering of a copper target biased to Ϫ600 V. The crystallographic structure and surface morphology of copper films were determined by x-ray diffraction techniques and atomic force microscopy, respectively. The magnitude of residual stresses developed in these films was calculated from the radius of curvature of Si substrates. The electrical resistivity of films was deduced from the thickness and sheet resistance of films determined by profilometry and four point probe measurements. The evolution of the deposition rate, surface roughness, microstructure, magnitude of residual stresses, and electrical resistivity of films was investigated as a function of the substrate bias voltage. The major characteristics of copper films were found to vary significantly as the negative substrate bias voltage increased from Ϫ40 to Ϫ125 V or with increasing argon ion energy. The resputtering process of a fraction of copper atoms by energetic incident argon ions was responsible for the modification of characteristics of films deposited on biased substrates. The quality of copper films in terms of surface morphology and electrical resistivity in particular was found to be excellent for incident argon ion energy values lower than 70 eV.
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