Abstract:

The synthesis and characterization of several ternary alkali and alkaline earth ruthenates are reported. Primary characterization techniques included x-ray and neutron diffraction, magnetic susceptibility, magnetization vs. applied magnetic field measurements and specific heat measurements.

The crystal structure of Na3 RuO4 , determined by powder neutron diffraction, is reported. The structure consists of isolated tetramers of edge sharing RuO6 octahedra in the ab plane, creating isolated 4-member plaquettes of Ru atoms comprised of two equilateral triangles sharing an edge. Magnetic susceptibility measurements reveal an antiferromagnetic-like transition at ~29 K, with [straight theta] w = -141 K. Neutron diffraction data indicate the onset of three-dimensional magnetic ordering at 29 K.

The structures of NaRu2 O4 and Na2.7 Ru 4 O9 are refined using neutron diffraction. NaRu2 O 4 is a stoichiometric compound consisting of double chains of edge sharing RuO6 octahedra. Na2.7 Ru4 O9 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. NaRu2 O4 displays temperature independent paramagnetism with ?o =1.23*10-4 emu/molRu Oe. Na2.7 Ru4 O9 is paramagnetic, ? o =2.0*10-4 emu/molOe with ?w = -11.8 K and a Curie constant of 0.0119 emu/molOeK. Specific heat measurements reveal a small upturn at low temperatures, similar to the upturn previously observed in La4 Ru6 O19 . The electronic contribution to the specific heat (?) for Na2.7 Ru4 O9 was determined to be 15 mJ/moleRu K2 .

The synthesis and primary magnetic characterization of the Ca1-x REx RuO3 (RE=Nd, Pr; x=0.1, 0.2, 0.3, 0.4, 0.5) are reported. The structure of the parent compound, CaRuO3 , is maintained for the series, and refined cell parameters show a steady increase, attributed to reduction of Ru+4 to the larger Ru+3 with RE incorporation. Magnetic susceptibility data show an increase in susceptibility with increasing rare-earth concentration. The localized magnetic moments of the rare earth atoms are postulated to be responsible for this observed increase. After correcting for the rare-earth magnetic contribution, the Nd-doped compounds appear to remain paramagnetic, where the Pr-doped deviate from normal paramagnetic behavior at low temperature. No magnetic hysteresis is observed, indicating the doped compounds are not ferromagnetic.