Temperature-dependent structural behaviour of Bi2-xNdxRu2O7-d, x=0.625 and 1.375

Powder neutron diffraction measurements were carried out for the pyrochlore-type oxides Bi2-xNdxRu2O7-d, x = 0.625 and 1.375, from T = 6 K to RT in order to probe the structural changes that occur on going from the metallic oxides, x < 0.75, to the semi-conducting oxides, x > 0.75. There is no evidence of any structural phase transition in either sample. The Rietveld refinements for Bi0.625M1.375Ru2O7-d and Bi1.375Nd0.625Ru2O7-d reveal that both the Ru-O bond length and Ru-O-Ru bond angle vary continuously with temperature. In both oxides there was evidence for static disorder of the Bi cations. The study gave further evidence on the requirements of a metallic state in ruthervate pyrochlore, i.e. Ru-O-Ru angle is greater than 132.5 degrees and that there is an appreciable amount of vacancies on the oxygen site of the Bi2O sublattice. (c) 2006 Elsevier B.V. All rights reserved.