The defect structure of Ca-stabilized material was described in terms of a correlated distribution of micro-domains within the cubic matrix. The structure comprised 2 types of defect. These were micro-domains that were based upon a single O vacancy with relaxed neighboring ions, and micro-domains which were based upon a pair of O vacancies that were separated by a distance of 3/2a along <111> directions. A combined analysis of neutron and X-ray data showed that a previously accepted structure, for the single vacancy domain, would have to be modified. That is, all of the cations next to the O vacancy were expected to be Zr. This modified model led to a good agreement between observed and predicted neutron and X-ray diffraction patterns.

T.Proffen, R.B.Neder, F.Frey: Acta Crystallographica, 1996, B52[1], 59-65