Lattice dynamics and superionic transition in ceria from first principles

We show how lattice dynamics in high-temperature ceria, CeO₂, can be studied beyond the quasiharmonic approximation [1]. The results indicate that the previously proposed precursor for the transition to the superionic phase is an artifact of the failure of the quasiharmonic approximation. We further directly observe the superionic transition at high temperatures [2] in our ab initio molecular dynamics simulations and find that it is initiated by the formation of oxygen Frenkel pairs. The Frenkel pairs are shown to form in a collective process involving simultaneous motion of two oxygen ions.

[1] J. Klarbring, N. V. Skorodumova, and S. I. Simak, Phys. Rev. B 97, 104309 (2018).
[2] J. Klarbring and S.I. Simak, Phys. Rev. Lett. (2018), accepted.