Antisite exchange defects in LiFePO4 crystals with an ordered olivine structure were visualize by using annular dark-field scanning transmission electron microscopy. A recognizable bright contrast was observed in some of the Li columns of scanning transmission electron microscopy images in a sample annealed at lower temperatures, which directly demonstrated disordered occupation by Fe atoms. Such exchange defects appeared to be locally aggregated rather than homogeneously dispersed in the lattice, although their overall concentration was fairly low. The present study emphasized the significance of atomic-level observations for defect distributions that could not be predicted by macroscopic analytical methods.

Atomic-Scale Visualization of Antisite Defects in LiFePO4. S.Y.Chung, S.Y.Choi, T.Yamamoto, Y.Ikuhara: Physical Review Letters, 2008, 100[12], 125502