3. Ionic conductivity. Finally, we consider the possibility of stabilisation of the cubic fluorite phase due to ionic di↵usion. From an AIMD simulation at 2500 K, we observe the spontaneous formation of Frenkel defect pairs consisting of an oxygen vacancy and an interstitial oxygen atom as shown in Fig. . This leads to spontaneous di↵usion even in a stoichiometric zirconia sample following the mechanism previously proposed for other fluorite type structures including CeO 2 . In this mechanism, one oxygen atom enters an interstitial site immediately followed by another oxygen atom occupying the empty site. Thus, a Frenkel defect pair is created, and vacancy mediated di↵usion can now occur throughout the material.