35 research outputs found
Novel Synthesis and High Pressure Behavior of Na0.3CoO2 x 1.3 H2O and Related Phases
We have prepared powder samples of NaxCoO2 x yH2O using a new synthesis
route. Superconductivity was observed in Na0.3CoO2 x 1.3H2O between 4 and 5K as
indicated by the magnetic susceptibility. The bulk compressibilities of
Na0.3CoO2 x 1.3H2O, Na0.3CoO2 x 0.6H2O and Na0.3CoO2 were determined using a
diamond anvil cell and synchrotron powder diffraction. Chemical changes
occurring under pressure when using different pressure transmitting media are
discussed and further transport measurements are advocated.Comment: 7 pages, 4 figures, PRrapid submitte
Bohmian mechanics, the quantum-classical correspondence and the classical limit: the case of the square billiard
Square billiards are quantum systems complying with the dynamical
quantum-classical correspondence. Hence an initially localized wavefunction
launched along a classical periodic orbit evolves along that orbit, the
spreading of the quantum amplitude being controlled by the spread of the
corresponding classical statistical distribution. We investigate wavepacket
dynamics and compute the corresponding de Broglie-Bohm trajectories in the
quantum square billiard. We also determine the trajectories and statistical
distribution dynamics for the equivalent classical billiard. Individual Bohmian
trajectories follow the streamlines of the probability flow and are generically
non-classical. This can also hold even for short times, when the wavepacket is
still localized along a classical trajectory. This generic feature of Bohmian
trajectories is expected to hold in the classical limit. We further argue that
in this context decoherence cannot constitute a viable solution in order to
recover classicality.Comment: Figures downgraded to low resolution; To be published in Found. Phys.
(2009)
new sol-gel synthetic route to phospho-olivines as environmentally friendly cathodes for li-ion cells
A new promising sol-gel synthesis of phospho-olivines asenvironmentally friendly cathode materials for Li-ion cells
Anewsol-gel synthetic route was developed to prepare single-phase phospho-olivines LiMPO4 (M=Fe or Mn) as environmentallyfriendly, low-cost potential cathodematerials for the next generation of Li-ion secondary batteries. Li2CO3 and M(II) acetate were used as Li and M(II) precursor while tri-ethyl phosphate was chosen as phosphate organic precursor for its high hydrolysis activity, with absolute ethanol as solvent. The sol-gelsynthesis ensures homogeneity of the precursors at the nanometric scale and improved reactivity, allowing to obtain very small agglomerates and crystal grain size. Several carbon sources were used in order to improve the electrochemical performances of the samples, increasing their electronic conductivity and hindering particle agglomeration. The powders were annealed at various temperatures in flowing Ar to avoid M(II) oxidation. The crystal structures of the products were analysed by Rietveld refinement of X-ray powder diffraction (XRD) data while the morphology of the samples was analysed by scanning electron microscopy. Galvanostatic cycling tests of the cathodic materials were made on coin cells with Li metal as anode in order to study the influence of the synthesis and the structural-morphological characteristics on the electrochemical performance of the phosphate/C composite