Are Barium Ruthenates Interesting?

We argue that there are at least three characteristics that make barium ruthenium oxides interesting. The first of these is the multifaceted formal valence of the Ru ions present, second is the Ru-O hybridization, which leads to “fractional” Ru oxidation states in some cases and the widespread existence of low resistivity metallic conductors among ruthenates, and third is the peculiar two-dimensional geometry (which includes pentagons) of some of the Ba-O layers present.