THE CRYSTAL-STRUCTURE AND ELECTRONIC-PROPERTIES OF BA4RU3MO12 (M = LI, NA, MG, ZN)

The crystal structures of two new hexagonal perovskites, 6H-Ba4Ru3LiO12 and 8H-Ba4Ru3NaO12, have been refined from neutron powder diffraction data. The former showscch stacking of the pseudo-close-packed BaO3 layers in space groupP63/mmc, a = 5.7828(1) andc = 14.1917(4)A °. The structure contains Ru2O9 dimers linked together by vertex-sharingMO6 octahedra, whereM represents a disordered distribution of Ru and Li. Ba4Ru3NaO12 has accch stacking sequence in space groupP63mc, a = 5.8142(1) andc = 19.2643(4)A °. The structure contains Ru2O9 dimers linked by vertex-sharing RuNaO11 groups. Magnetic susceptibility measurements suggest that both compounds are magnetically ordered at low temperatures. Electrical conductivity measurements show that both are semiconductors. The preparation and electronic properties of the mixed valence compounds Ba4Ru3MgO12 and Ba4Ru3ZnO12 are also discussed. © 1992 Academic Press, Inc. All rights reserved.