where x is the fraction of occupied interstitials. The result is shown in Fig. , and it is noted that at a defect concentration of only ⇠3 %, the configurational entropy is 0.01 meV atom 1 K 1 , which at the high temperatures considered here (⇠2500 K) amount to a significant energetic stabilisation on the same order as the free energy di↵erence between cubic and tetragonal phases. Thus, it appears that cubic zirconia could be stabilised by configurational entropy arising from partial melting of the oxygen sublattice through the spontaneous formation of Frenkel defect pairs.