Influence of octahedral tilting and composition on electrical properties of the Li0.2-xNaxLa0.6TiO3 (0 <= x <= 0.2) series Articles uri icon

publication date

  • June 2008

start page

  • 495

end page

  • 502

issue

  • 13-14

volume

  • 179

International Standard Serial Number (ISSN)

  • 0167-2738

Electronic International Standard Serial Number (EISSN)

  • 1872-7689

abstract

  • 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 ~ 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 (np = 0.27). Below the percolation threshold, Li ions only display local mobility, remaining confined into small domains of perovskites.

keywords

  • lanthanum lithium titanate; high-temperature neutron diffraction; perovskite structure; vacancy percolation threshold; ionic conductivity