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

Influence of Octahedral Tilting and Composition on Electrical Properties of the Li0.2−xNaxLa0.6TiO3 (0 ≤ x ≤ 0.2) Series. R.Jimenez, A.Varez, J.Sanz: Solid State Ionics, 2008, 179[13-14], 495-502