Paper reports the results of the neutron scattering study of crystal structure and diffusion of Cu2-delta Se compounds in superionic alpha-phase. We found that the crystallographic model with Cu atoms in the 8c (0.25, 0.25, 0.25) and 32f (x, x, x) (x = 0.33-0.39) sites in fluorite lattice provides the best description of the average structure. The quasi-elastic neutron scattering data reveal the decrease of the self-diffusion coefficient with the deviation from the stoichiometry due to the longer residence time of Cu atoms between diffusion hops. Combination of neutron diffraction, quasi-elastic scattering experimental data with the Bond-Valence Method simulations strongly suggests that the Cu atoms diffuse between the nearest 8c sites through the 32f sites. (c) 2012 Elsevier B.V. All rights reserved.