It should be noted that this description only takes into account the configurational entropy in the cubic phase, and not a similar entropy in the tetragonal phase. Thus, a likely mechanism is that upon heating, Frenkel defect pairs are created in the tetragonal phase, and since these are created at random positions with random relative orientations, an isotropic "pressure" is exerted upon the crystal resulting in an overall average cubic symmetry. This is similar to the stabilisation mechanism in yttriastabilised-zirconia (YSZ), where the Y substitutions are compensated by oxygen vacancies. Here, it has been shown that the stabilisation of the cubic phase can be attributed solely to the oxygen vacancies .