Defect chemistry and lithium-ion migration in polymorphs of the cathode material Li₂MnSiO₄

The search for new low-cost and safe cathodes for next-generation lithium batteries has led to increasing interest in silicate materials. Here, a systematic comparison of crystal properties, defect chemistry and Li-ion migration behaviour of four polymorphs of Li2MnSiO4 is reported based on the results of atomistic simulations. The four polymorphs examined have Pmn21, Pmnb, P21/n, and Pn symmetry. Lattice energies of all four polymorphs are very similar, with only a small energy preference for the two orthorhombic phases over the monoclinic phases, which explains the difficulty experimentalists have had preparing pure-phase samples. Defect formation energies of the polymorphs are also similar, with antisite Li/Mn defects the most energetically favourable. Detailed analysis of the Li-ion migration energy surfaces reveals high activation energies (around 0.9 to 1.7 eV) and curved trajectories. All four polymorphs are thus expected to be poor Li-ion conductors, requiring synthesis as nanoparticles to facilitate sufficient Li transfer. The results accord well with experimental reports on the structure, relative phase stabilities and electrochemical performance of materials in this system

Electrical conductivity of brownmillerite-structured oxide ceramics

SIGLEAvailable from British Library Document Supply Centre-DSC:D192183 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Search for sleptons in e+ e- collisions at center-of-mass energies of 161-GeV and 172-GeV

The data recorded by the ALEPH experiment at LEP at centre-of-mass energies of 161 GeV and 172 GeV were analysed to search for sleptons, the supersymmetric partners of leptons. No evidence for the production of these particles was found. The number of candidates observed is consistent with the background expected from four-fermion processes and gammagamma-interactions. Improved mass limits at 95% C.L. are reported.Comment: 17 pages, 3 figures, submitted to Phys. Lett.