ABSTRACT
Comprehensive studies have been undertaken, inclusive of experimental and computational techniques, on the structure and cation distribution of spinel solid solutions formed between the normal spinel LiMn2O4 and inverse LiFe5O8. Series of solid solutions of a composition (1 - x)LiMn2O4 x xLi0.5Fe2.5O4 are single phase products with spinel structure in the whole range of x, displaying a cubic structure. With increasing Fe3+ content, the tendency of ordering by lithium ions in octahedral spinel sites and a strongly marked preference of Li+ cations to occupy the octahedral positions is apparent. Modelling and refinement of crystal structure of such spinel solid solution series have been undertaken by the energy minimisation procedure, together with the interatomic potentials calculation, explaining some divergences of the experimental data.
ABSTRACT
Lithium manganese oxides in the form of cubic spinel phases (space group Fd3m) are formed in a LixMn3-xO4 system for rather limited values of x. Structural investigations by X-ray powder diffraction, applied to the Li-Mn-O compounds, indicate the formation of a second crystalline phase, Li2MnO3 (space group C2/m), with the increasing lithium content. Total Li+ content per unit cell and the cation distribution over a spinel lattice in LixMn3-xO4 have been studied by measurements of integrated intensities of X-ray reflections, and by structure refinement using Rietveld profile analysis. In an attempt to understand the factors affecting cation distribution in the spinel lattice, we applied the computer modelling techniques and investigated the Li+, Mn3+ and Mn4+ ion distribution by calculating the lattice energy, combined with energy minimisation procedures, using the General Utility Lattice Program (GULP), a program designed for simulation of ionic and semi-ionic solids, based on interatomic potential models.
