Ionic Diffusion in a Ternary Superionic Conductor: AnAb InitioMolecular Dynamics Study

We present Car-Parrinello molecular dynamics simulations of a novel superionic conductor, ${\mathrm{Li}}_{2-2x}{\mathrm{Mg}}_{1+x}\mathrm{Si}$ $\left(x\sim 0.06\right)$, at different temperatures. The calculations clarify the nature of the ionic conduction and lead to the prediction of the first inorganic magnesium superionic conductor. In fact, both lithium and magnesium are found to act as charge carriers. The diffusion is fast and can be described as vacancy migration through directed jumps. The calculated diffusion constants for lithium are consistent with recent electrochemical measurements.