An ab initio molecular dynamics study of ionic conductivity in hexagonal lithium lanthanum titanate oxide La 0.5 Li 0.5 TiO 3

Abstract

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO3 oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) ${\rm Li}_{3x} {\rm La}_{\left( {{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-\nulldelimiterspace} 3}} \right) - x} \Box_{\left( {{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} \right) - x} {\rm TiO}_3 $ and its structurally related materials. In this formula, $\Box$ represents the vacancy. These materials have attracted much attention due to their application in lithium ion batteries used as energy sources in microelectronic and information technologies. In addition to the well-established simple cubic, tetragonal and orthorhombic perovskite type distorted cell structures, the hexagonal unit cell was reported in a recent study for Li0.5 La0.5 TiO3 − δ , $\left( {0 \le \delta \le 0.06} \right)$ . We investigated the ionic conductivity in hexagonal ${\rm La}_{0.5} {\rm Li}_{0.5}\- {\rm TiO}_3 $ by molecular dynamics. We confirmed that ionic conductivity in this compound is due to the motion of lithium ions. We show that both Arrhenius and Vogel–Tamman–Fulcher-type relationships could be used to express the high-temperature conductivity of this compound. From our results, hexagonal LLTO exhibits almost 1.7–1.9 ×10 − 3 S cm − 1 at room temperature. Thus, due to its high ionic conductivity, this compound is expected to show some advantages in comparison with the best conductors of this family, for usual applications of ionic conductors.