New cubic defect pyrochlore type A(x)Ln(y)Sb(2)O(6+z) antimoniates (0 < x, y, z < 1; A = Rb, Cs, Tl; Ln = Eu, Gd, and Y) (space group Fd3m) were prepared by calcination in air at 650degreesC of compositions obtained by a coprecipitation method. Their crystal structures were refined by the Rietveld procedure and further confirmed by X-ray absorption spectroscopy (EXAFS) experiments. Refinements of the X-ray powder diffraction data show a partial and statistical occupation of the 8b site by alkaline or thallous ions and oxygen and lead to values close to 0.33 for the only refinable positional x parameter of the 48f oxygenated site. (C) 2003 Elsevier Ltd. All rights reserved.