Structure and magnetism of NaRu2O4 and Na2.7Ru4O9

The structures of NaRu2O4 and Na2.7Ru4O9 are refined using neutron diffraction. NaRu2O4 is a stoichionietric compound consisting ;of double chains of edge sharing RuO6 octahedra. Na2.7Ru4O9 is a non-stoichiometric compound with partial occupancy of the Na sublattice. The structure is a mixture of single, double and triple chains of edge-shared RuO6 octahedra. Na2.7Ru6O4 displays temperature independent paramagnetism with chi(0) = 1.23 x 10(-4) emu/mol(Ru) Oe. Na2.7Ru4O9 is paramagnetic, chi(0) = 2.0 x 10(-4) emu/mol Oe with Theta(w) = -11.8 K and a Curie constant of 0.0119 emu/mol Oe K. Specific heat measurements reveal a small upturn at low temperatures, similar to the upturn observed in La4Ru6O19. The electronic contribution to the specific heat (gamma) for Na2.7Ru4O9 was determined to be 15 mJ/mole(Ru) K-2. (c) 2005 Elsevier Inc. All rights reserved.