Fluorite-like cluster

As follows from Fig. 2d, contrarily to the pure ceria sample, samples of mixed fluorite-like solid solutions retain molecular forms of oxygen (O2 [16]). The intensity of those bands is higher for samples containing calcium, fluorine and smaller amount of zirconium. It seems to correlate with the decreased ability of those systems to dissociate molecular oxygen due to a lower density of either highly unsaturated cations or clustered centers. 

The interaction of lattice defects in fluorite-like solids under conditions when the thermal motion is restricted, leads to self-assembling of the long-living metastable globular clusters. The same effect was observed in hyper-stoichiometric and radiation-damaged UO2+X Yakub, 2008). At elevated... 

The presence of defects clusters in disordered solid solutions was confirmed by direct experimental methods (neutron diffraction, F NMR, EXAFS, etc.) as well as indirectly, using results of X-ray and electron diffraction studies of ordered fluorite-like phases having close compositions [7]. 

Such Frenkel type defects are known to exist in many anion excess fluorite related compounds forming clusters, at higher defect concentration, like in U409 a, [14J. This interstitial oxygen was made responsible for the excellent behaviour of ceria as an oxygen storage medium. 

The following clustering and probably local cluster ordering (similar to fluorites, see Section 14.5.2) in the structure leads to a decrease of the charge carrier concentration and to a blocking of a part of the conductivity channels. It negatively affects the transport properties of these phases. AU these factors lead to the appearance of a maximum on the curve of conductivity, a=f(x) atx = 0.05 (Figure 14.38). Similar extremes were observed on concentration dependences of transfer characteristics of tysonite-like MxRi xF3 2x (M = Ca, Sr, R = La-Lu) solid solutions [115]. 

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