Ionic conductivity of Dion-Jacobson type oxide LiLaTa2O7 and oxynitride LiLaTa2O6.15N0.57 measured by impedance spectroscopy

摘要

Ionic transport in the layered perovskite, LiLaTa2O7, and its oxynitride derivative, LiLaTa2O6.15N0.57, were examined by ac impedance spectroscopy in a N-2 atmosphere. Non-Arrhenius behavior was observed when LiLaTa2O7 was heated from 30 degrees C to 70 degrees C with the conductivity decreasing from 10(-5.9) S/cm to 10(-6.3) S/cm, due to the heat-induced removal of interlayer water. The conductivity of dehydrated LiLaTa2O7 then increased monotonously from 10(-6.3) S/cm at 80 degrees C to 10(-3.7) S/cm at 283 degrees C with an activation energy (E-a) of 0.54 eV. Compared to LiLaTa2O7, the oxynitride phase, LiLaTa2O6.15N0.57, exhibited much lower conductivity ranging from 10(-6.7) S/cm at 315 degrees C to 10(-5.5) S/cm at 496 degrees C with an E-a of 0.57 eV. The distinct ionic conductivity among the similar layered perovskites, LiLaTa2O7, LiLaTa2O6.15N0.57, Li2La2/3Ta2O7, and Li2LaTa2O6N, highlights the importance of structural factors on the ionic conductivity, particularly, the site occupancy of the mobile cation, Li+, and the connectivity of the anion sublattice. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.