THE CRYSTAL-STRUCTURE OF THE SPIN-GLASS PYROCHLORE, Y2MO2O7

The crystal structure of the spin-glass material, Y//2Mo//2O//7, has been determined from powder neutron diffraction data using profile (Rietveld) methods. The data are consistent with the fully ordered cubic pyrochlore structure, a//0 equals 10. 230(1) A with Y in 16d, Mo in 16c, O in 48f(x equals 0. 3382(1)), and O prime in 8b of Fd3m. Attempts to refine models with O prime disordered over the 32e sites or between the 8a and 8b sites resulted in convergence to the 8b positions. Derived Y-O and Mo-O distances are in excellent agreement with those found in isostructural materials giving indirect evidence for Y-Mo ordering over the cation sites.