A promising group of inorganic salts recently emerged for the negative electrode of advanced lithium-ion batteries. Manganese carbonate combines low weight and significant lithium storage properties. Electron paramagnetic resonance (EPR) and magnetic measurements are used to study the environment of manganese ions during cycling in lithium test cells. To observe reversible lithium storage into manganese carbonate, preparation by a reverse micelles method is used. The resulting nanostructuration favors a capacitive lithium storage mechanism in manganese carbonate with good rate performance. Partial substitution of cobalt by manganese improves cycling efficiency at high rates.

No abstract

No abstract

No abstract

The average magnetic susceptibilities for trivalent rare earth (R 3+ ) ions in polycrystalline tetragonal rare earth oxybromides (ROBr, R ¼ Ce-Nd, Sm, Eu, and Tb-Yb) were measured between 2 and 298 K. The susceptibilities of all ROBr follow the paramagnetic Curie-Weiss behaviour down to low temperatures except for SmOBr and EuOBr where the effect of crystal field was observed already above 200 K. The observed effective magnetic moments m eff (RT) were generally higher than the free ion values. For the heavier R 3+ ions (Ho 3+ and Er 3+ ) m eff was found to be less than the free ion value due to crystal field mixing in the opposite way. The Weiss constant y was found to be negative for all ROBr, suggesting antiferromagnetic (AFM) ordering at lower temperatures but only SmOBr (SmOCl) and DyOBr (DyOCl) show such ordering at 5(8) and 8(11) K, respectively. The increasing interlayer distance between adjacent (RO) nþ n layers from ROCl to ROBr and within the ROBr series lowers the Ne ´el temperature. AFM ordering thus depends on the 3D interactions while 2D interactions have negligible effect. The temperature dependence of the experimental paramagnetic susceptibility for each ROBr was simulated with the aid of the van Vleck formalism based on the wave functions and energy level values obtained from spectroscopic data. Lattice expansion and consequent modifications in crystal field caused discrepancies at higher temperatures.

The scheelite form of the TbCrO 4 oxide has been obtained by treating TbCrO 4 -zircon at 4 GPa and 823 K. X-ray and neutron diffraction data reveal that the high-pressure polymorph of TbCrO 4 crystallizes with tetragonal symmetry space group I4 1 / a and lattice parameters a = 5.036 74͑10͒ Å and c = 11.3734͑4͒ Å. Although bisdisphenoids ͓TbO 8 ͔ and tetrahedra ͓CrO 4 ͔ are present in both scheelite and zircon polymorphs, the remarkable changes observed in both polyhedra appear to support the reconstructive model for the zircon-scheelite first-order phase transition. Specific heat and neutron diffraction measurements confirm the antiferromagnetic ordering previously proposed from magnetic susceptibility measurements, in which both Tb 3+ and Cr 5+ sublattices are involved. The magnetic structure has been determined and can be described on the basis of the coincidence between the chemical and magnetic cells, k = ͑0,0,0͒, where the magnetic moments of the Tb

No abstract

No abstract