From our MLMD data, we first compute the constant volume heat capacity as a function of temperature. We identify a peak at T s = 625 K, which we assign as the superionic transition temperature. We observe non-Arrhenius diffusion behaviour, characterised by a discontinuous change in the activation energy for the Li + selfdiffusion coefficient, D * , at T s . Analysis of the Li substructure in terms of point defects reveals that some proportion of Li + ions move from Li(2) sites, forming Li(2) vacancies and doubly occupied Li(2) or Li(1) sites. Considering Li vacancy concentrations as a function of temperature reveals similar behaviour to that for the Li + selfdiffusion coefficient. Li(2) vacancy concentrations show non-Arrhenius behaviour with a discontinuous change in formation activation energy at T s . The relative change in Li(2) vacancy formation activation energy across the superionic transition is quantitatively similar to the corresponding change in D * , which suggests that the superionic transition in Li 3 N might be explained by a decrease in the energy required to create defect pairs by displacing Li + ions from the Li(2) sites at T s .