The structures of these O-deficient pyrochlores were refined by means of the Rietveld analysis of time-of-flight neutron powder diffraction data. The diffraction data for Ir2Pb2O6.5 showed that the structure belonged to F¯4¯3m, with a = 1.026450nm, and exhibited an O vacancy ordering in which each Pb atom was displaced by 0.004nm towards its associated vacancy. In the case of Bi2Ir2O7, the structure belonged to Fd3m, with a = 1.03256nm, and the O vacancies were randomly distributed over the O sites. In both structures, the Ir atoms exhibited an almost regular octahedral coordination whereas the Bi and Pb cations had a distorted 8-fold coordination geometry.

B.J.Kennedy: Journal of Solid State Chemistry, 1996, 123[1], 14-20