Structural and Bonding Trends in Ruthenium Pyrochlores
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Abstract The structures of four semiconducting ruthenium pyrochlores,Ln2Ru2O7(Ln= Pr, Nd, Tb, and Yb) have been determined by Rietveld refinement of powder neutron diffraction data. These structures, when compared with those of other Ru containing pyrochlores, especially the metallically conducting pyrochlores, demonstrate that the differences in the Ru–O bond distances between metallic and semiconducting ruthenium pyrochlores are small and highlight the importance of the easily polarizable group 13/15 cations in facilitating large Ru–O–Ru angles. While Ru–O–Ru angles greater than 133° are undoubtedly necessary to facilitate metallic conductivity, it appears that electron delocalization from theAsite cation is at least equally important.