Concentration and mobility of mobile Li+ ions in Li6BaLa2Ta2O12 and Li5La3Ta2O12 garnet lithium ion conductors

Abstract

The concentration of mobile ions, nc, and their mobility are important factors that control the conduction process in ionic conductors. The analysis of the conductivity spectra of Li6BaLa2Ta2O12 (LBLT) and Li5La3Ta2O12 (LLT) Li+ conducting garnets at low temperatures helps us to estimate the values of nc of Li+ ions and their mobility. We found that nc is independent of temperature with an average values of 1.93 × 1021 and 6.71 × 1020 cm−3 for LBLT and LLT, respectively. These values of nc represent only a small fraction of 8.79 % (in LBLT) and 3.52 % (in LLT) out of the total Li+ ions content. Our results confirm that the conduction process is controlled by the mobility of Li+ ions, which is related to the occupancy of Li+ in the tetrahedral sites of the garnet phases. Moreover, the diffusivity of Li+ has been estimated at different temperatures and compared to other fast Li+ conductors.