In Li 3 OCl, ionic conductivity is attributed to the diffusion of mobile point defects-specifically lithium vacancies and lithium interstitials . Lithium vacancies and interstitials in Li 3 OCl are both predicted to be mobile at room temperature, with calculated diffusion barriers of ∼0.3 eV and ∼0.15 eV, respectively . While these diffusion barriers indicate that lithium interstitials are significantly more mobile than lithium vacancies, calculated defect-pair formation energies give a lower formation energy for [V Li + V Cl ] Schottky pairs (1.0 eV to 1.6 eV) than for [V Li + Li i ] Frenkel pairs (1.9 eV to 2.5 eV) , making lithium vacancies the expected dominant charge-carrying defect species in undoped Li 3 OCl.