Complex behavior in quaternary zirconias for inert matrix fuel: What do these materials look like at the nanometer scale?

Conventional crystallographic analysis of cubic stabilised zirconias (CSZ) over a wide range of stabilisers and stoichiometries has shown O atom displ acements along lattice vectors and cation disorder with irreproducible char acteristics. However, because diffraction is only sensitive to the average long-range order and biased towards periodic and symmetric distortions, it is essential to supplement it with probes of short-range order that may rev eal additional, element-specific details about local ordering. We have perf ormed X-ray Absorption Fine Structure (XAFS) spectroscopy measurements on a series of Er-Y-(U-Ce)-Zr oxides to determine the local environment around each of the cations. Results from these experiments demonstrate that not on ly are there significant element- and composition-dependent distortions awa y from the crystallographic structure but also interactions between specifi c pairs of the metal ions indicative of cooperative behaviour. This suggest s that some of the metal ions are not randomly, isomorphically substituted into the lattice but instead have tendencies to form nanometer-scale cluste rs and networks. In this respect, substantial differences are seen in the i nfluence of Ce and U on the Y-centered distortions, consistent with differe nt roles for these two elements in inert matrix fuel (IMF) matrices. This t ype of nanometer scale heterogeneity is typically coupled to the phase stab ility and other properties of other materials and may therefore be importan t to these zirconias in their IMF application. (C) 2001 Published by Elsevi er Science Ltd. All rights reserved.