Synthesis and structural analysis of Bi2−y Sr y Ir2O7, a new pyrochlore solid solution

Abstract: This paper presents a study of the synthesis and structural properties of the new pyrochlore-type Bi2−y Sr y Ir2O7 series. Ten compositions with 0.0≤y≤0.9 were prepared by solid-state reaction with thermal treatments at 873, 1073 and 1323K under atmospheric pressure conditions. Structural refinements from X-ray powder diffraction data by the Rietveld method show that all compounds of the Bi2−y Sr y Ir2O7 solid solution crystallize in a α-pyrochlore structure. The main structural difference when bismuth is substituted by strontium concerns the x position of the O1 (x, ⅛, ⅛). This substitution significantly increases the Bi/Sr–O1 distance and diminishes the Ir–O1 distance; this implies that the Ir–O1–Ir bond angle increases. With the Sr substitution, the IrO6 local configuration goes from a flattened trigonal antiprism, y<0.5, to an elongated one, y>0.5, passing through an octahedral array, y∼0.5. The electrical consequences of these structural changes observed in this system are qualitatively explained with electronic structure calculations, this behavior agrees very well with those observed in other pyrochlore systems A 2 M 2O7 (A=rare earth cations or Tl+, Pb2+, or Bi3+, and M=Ru or Ir). [Copyright &y& Elsevier]