Modeling Li-ion conductivity in fast ionic conductor La2/3-xLi3xTiO3

Monophasic samples of fast ionic conductors La2/3 - x Li3xTiO3 (LLTO), with x varying from 0.06 to 0. 13, are prepared by solid-state reaction. The total dc-conductivity is measured by complex impedance spectroscopy in the 10 MHz - 1 Hz frequency range. Considering only the resulting location of oxygen atoms and employing bond valence equations, the conduction geometry and dc ionic conductivity are modeled. An averaged pathway for the Li+ conduction is proposed in this paper, assuming that the time-averaged position for Li+ is the geometrical centre of the A-cage. The saddle point of this pathway (Vumax) can be related to the activation energy for the ionic jump. Moreover, in order to model dc-ionic conductivity, not only activation energy, but also number of carriers and site occupancies have been considered. We propose three possibilities for the Li+ location in the structure in order to predict bulk conductivity in LLTO phase. Experimental evidence allows the exclusion of one of the three possibilities, while the other two are both in agreement with experimental values. (C) 2002 Elsevier Science B.V. All rights reserved.