Density Functional Theory Study for the Stability and Ionic Conductivity of Li2O Surfaces

The energetic, electronic, and defect properties of two low-index Li2O 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 Li2O materials.