Distribution of the M-M Distances in the Rare Earth Oxides

Abstract

A systematic study of the distribution of the M—M distances in all the binary, ternary and quaternary oxides of the rare earth elements (RE = Sc, Y, La–Lu), contained in the Inorganic Crystal Structure Database (ICSD) has been carried out. The results indicate that the RE—RE distances are not distributed uniformly, but present maxima which are close to the corresponding distances in the pure metals. In some of the histograms (Y, Ce, Pr, Sm, Tb, Dy, Ho, Lu) two maxima appear which correspond to the nearest-neighbor (b.c.c., h.c.p.) and second-nearest neighbor (b.c.c.) distances of the elemental phases. As examples of this behavior, the cation arrays of the binary oxides, hydroxides and ternary oxides of both the delafossite and \alpha-NaFeO2 type are analyzed. In all of them the cations form aggregates whose topologies and distances can be related to the structure of the parent metals. The size of the metal aggregates seems to decrease with increasing oxygen content.