Crystallographic facetting in solid-state reacted LiMn2O4 spinel powder

Surface facetting on lithium manganate (LiMn2O4) spinel crystallites prepared via mixed oxide route has been studied by transmission electron microscopy (TEM). As-calcined powder particles from solid-state reaction at 800°C for 4 h, featuring a cubo-octahedral shape, exhibit facetting predominantly on {1 1 1}, {1 0 0} and {1 1 0}. The facetted planes of {1 1 1} are retained upon further annealing when others of {1 3 1}, {1 0 0} gradually mitigated, but the cubo-octahedral crystal form persists even after they have been post-calcination annealed at 800°C for 100 h. The {1 1 1} planes of the lowest solid-to-vapour surface energy have grown upon annealing at the expense of {1 0 0} of higher solid-to-vapour surface energy. Annealed LiMn2O4 crystallites also exhibit both the positive and negative tetrahedron, with one of which being better developed, indicating a lower symmetry space group of F4̄3m.