Oxide Ion Disorder in Nd₂Hf₂O₇

The compound Nd₂Hf₂O₇ was synthesized via a solid-state route and the crystal structure determined by electron diffraction and Rietveld refinement of both X-ray and neutron diffraction data. A small amount of disorder was found on the anion sublattice, while no evidence of disorder in the cation sublattice could be verified. The compound is cubic with space group Fd3m, structurally lying between the ideal pyrochlore and fluorite forms, with 0.26% of the oxide ions residing on the 8a sites usually vacant in pyrochlores. The lattice constant is 10.6469(2) Å, and the overall fit parameter was R_wp=0.0398.