Interrelationship between Li+ diffusion, charge, and magnetism in 7LiMn2O4 and 7Li1.1Mn1.9O4 spinels: Elastic, inelastic, and quasielastic neutron scattering

Using quasielastic neutron scattering (QENS), we have investigated a self-diffusive behavior of Li+ ions for both (LiMn2O4)-Li-7 and (Li1.1Mn1.9O4)-Li-7 spinels. In addition, we have carried out elastic and inelastic neutron scattering measurements using the same samples, to study the interrelationship between Li+ self-diffusion, magnetism, and charge distribution in the lattice. From the QENS results, the self-diffusion of Li+ was observable above 280 K, and a self-diffusion coefficient (D-s(Li)) for (LiMn2O4)-Li-7 was estimated as similar to 10(-8) cm(2)/s at 400 K. D-s(Li) for (Li1.1Mn1.9O4)-Li-7 was comparable to that for (LiMn2O4)-Li-7. Furthermore, combining with the results of elastic and inelastic measurements, it was found that (Li1.1Mn1.9O4)-Li-7 undergoes a transition from a low-temperature (T) short-range charge-ordered (SRCO) phase to a high-T charge-disordered (CDO) phase at 280 K. The structure of the SRCO was determined as a hexagon, because the formation of hexagon spin clusters was deduced from a magnetic diffuse scattering at low T. Assuming the presence of the SRCO-CDO transition at 280 K, both the anomaly of the diffusive behavior at 280 K and the local lattice distortion below 280 K are reasonably explained, despite the absence of long-range CO for (Li1.1Mn1.9O4)-Li-7.