Computer simulation of translational and rotational dynamics inLiKSO4

A computer-simulation study of dynamics in ${\mathrm{LiKSO}}_4$ has been carried out at several temperatures using the molecular-dynamics technique. Above 300 K, the partial density of states shows a diffusive nature due to rotational jumps of sulfate ions. At 350 K, the rotational jumps are predominately about the hexagonal axis, while at much higher temperatures, jumps about other axes are also observed. Above 700 K, the diffusion of the lithium ions is not found to be appreciable, which is consistent with the known small conductivity in the ionic-conductor phase. However, the displacements of both the lithium and potassium ions are found to be large and comparable despite the large difference in the sizes of the two ions. The Li and K ions move to interstitial positions and vibrate there for fairly long times of a few picoseconds before returning to the lattice positions. These displacements are found to be related to the reorientations of the neighboring sulfates, which undergo large jumps of up to 180°.