Electronic structure calculations have been performed to explain the difference in the electronic properties of two crystallographic forms of ${\mathrm{BaRuO}}_3.$ The calculations can explain the qualitatively different resistivities of isoelectronic $4H$- and $9R$-${\mathrm{BaRuO}}_3$ below 100 K. The difference in symmetry between the hexagonal four-layer ${\mathrm{BaRuO}}_3$ and the rhombohedral nine-layer compound allows the formation of a gap for the later. The electronic structure of these hexagonal perovskites is compared with the more familiar cubic perovskite ${\mathrm{CaRuO}}_3.$

• Received 8 November 1999

DOI:https://doi.org/10.1103/PhysRevB.61.10005