Density functional theory study for the stability and ionic conductivity of Li₂O surfaces

The energetic, electronic, and defect properties of two low-index Li ₂O surfaces were studied theoretically at density functional level. In agreement with previous theoretical studies, it was found that the (111) surface is more stable than (110). For both surfaces, a slight shift of the position of the valence band maximum and conduction band minimum with respect to the bulk Li₂O was found. The formation of an isolated cation vacancy and a cation Frenkel defect in the Li₂O (111) surface were studied as a function of defect concentration. The defect formation energy is ~10% smaller on the (111) surface than in the bulk. Possible pathways for Li ⁺ diffusion in the Li₂O (111) surface were investigated. The activation energy for local hopping processes in the topmost surface layer is significantly smaller than in the Li₂O bulk, which is in agreement with experimentally observed increased conductivity in nanocrystalline Li ₂O materials.