  A potential superionic material LiY(SO$_4$)$_2$ has been excavated from the
published literatures because its synthesis method and experiment data implied
it exists the superionic state. We use \textit{ab initio} calculation to
analyzing the differences between solid state and superionic state. We found
the diffusion of Li$^+$ from the lattice site to the interstitial site will
change the nearest neighbor numbers of O atom from 4 to 8. In order to reduce
energy, the reorientation of SO$_4^{2-}$ must exist accompany with the
diffusion of Li$^+$ so the nearest neighbor number of O will keep about 5 in
the superionic state. Our work not only presents an example for discovering
materials from literatures based on prior knowledge but also reveals the
micromechanism of cation-anion coupled dynamics for superionic state.
