The electrical properties and the mechanism of lithium ionic diffusion in the Li7La3Ta2O13 compounds were investigated. The bulk and total conductivity at 300 K of the Li7La3Ta2O13 compound are about 3.3 x 10(-6) S/cm and 2.6 x 10(-6) S/cm, respectively. The activation energy of bulk and total conductivity is in the range of 0.38-0.4 eV. A prominent internal friction peak in Li7La3Ta2O13 compounds was observed around 280 K at 0.5 Hz, which is actually composed of two subpeaks (P-1 peak at lower temperature and P-2 peak at higher temperature). From the shift of peak position with frequency, the activation energy of 1.0 eV and the pre-exponential factor of relaxation time in the order of 10(-18)-10(-21) s were obtained if one assumes Debye relaxation processes. These values of relaxation parameters strongly suggest the existence of interaction between the relaxation species (here lithium ions or vacancies). Based on the coupling model, the relaxation activation energies are deduced as 0.45 eV and the pre-exponential factor of relaxation time as 10(-15) s. Judging from these relaxation parameters and the similarity of structure between Li7La3Ta2O13 and Li5La3Ta2O12 compounds, the P-1 and P-2 peaks are suggested to be related with the lithium ionic diffusion between 48g <-> 48g and 24d <-> 48g. (C) 2009 Elsevier B.V. All rights reserved.