Structure, electronic and magnetic characterization, and calculated electronic structures of two oxyhalide hexagonal perovskites

We report the crystal structures, initial magnetic and charge transport characterization, and calculated electronic structures of the hexagonal oxyhalide perovskites, ${\mathrm{Ba}}_{7}{\mathrm{Ru}}_{4}{\mathrm{O}}_{15}{\mathrm{Cl}}_{2}$ and ${\mathrm{Ba}}_{7}{\mathrm{Ru}}_{4}{\mathrm{O}}_{15}{\mathrm{Br}}_{2}$. The experimental information is obtained through the study of single crystals. Face-sharing $\mathrm{Ru}{\mathrm{O}}_{6}$ octahedra form ${\mathrm{Ru}}_{2}{\mathrm{O}}_{9}$ dimers in a layered triangular geometry in these materials; minor amounts of off-magnetic-site structural disorder are present in our crystals. Both are magnetically isotropic, with 2.5 \ensuremath{\mu}B/mol-Ru, Curie-Weiss theta \ensuremath{-}185 K, and 2.9 \ensuremath{\mu}B/mol-Ru, Curie-Weiss theta \ensuremath{-}168 K, respectively. Broad features in the magnetic susceptibility and heat capacity associated with magnetic ordering (at 35 and 37 K, respectively) are observed. The charge transport band gaps are 0.03 eV for the oxychloride and 0.006 eV for the oxybromide. There is no gap at the Fermi level for either of these compounds in density-functional theory electronic structure calculations.