The Rietveld analysis of ND patterns of polycrystalline Li0.2-xNaxLa0.6TiO3 (0 <= x <= 0.2) samples, recorded between 300 and 1075 K, shows an orthorhombic-tetragonal transformation, in which the octahedral tilting along the b axis is eliminated at similar to 773 K, but the vacancy ordering along the c axis remains. In Li rich samples, conductivity (10(-3) Omega(-1) cm(-1) at 300 K) departs from the Arrhenius behaviour, decreasing activation energies from 0.37 to 0.14 eV when octahedral tilting is eliminated. Successive Maxwell-Wagner blocking processes, detected in the real part of dielectric constant plots, have been ascribed to the Li blocking at interior domains, grain-boundary and electrode-electrolyte interfaces. The substitution of Li+ by Na+ decreases the amount of vacant A-sites, decreasing several orders of magnitude the conductivity when the amount of vacancies approaches the vacancy percolation threshold (n(p)=0.27). Below the percolation threshold, Li ions only display local mobility, remaining confined into small domains of perovskites. (c) 2008 Elsevier B.V. All rights reserved.