Subsurface Distribution of Antisite Defects in LiMnPO4: Direct Comparison with LiFePO4

Abstract

We demonstrate a thermodynamically stable distribution of antisite exchange defects within a single LiMnPO4 crystal through a combination of atomic-resolution scanning transmission electron microcopy and ab initio calculations. In contrast to the strong segregation of exchange defects in subsurface layers with selective orientations in LiFePO4, the highly ordered arrangement between Li and Mn in the bulk is preserved near the surface of LiMnPO4 crystals, showing no preferential aggregation of defects irrespective of the location in a particle. On the basis of the identical crystal structure and the analogous compositional basis of the two olivine phosphates, the distinct distribution characteristics of the antisite exchange defects are notably unexpected findings, highlighting the value of direct visualization at an atomic scale.