STRUCTURE OF Zr2ON2 BY NEUTRON POWDER DIFFRACTION: THE ABSENCE OF NITRIDE-OXIDE ORDERING

摘要

The structure of the fluorite-related Zr2ON2 has been refined against a combination of lab X-ray and time of flight neutron powder diffraction data. The structure is of the bixbyite (C-M2O3) type. The high symmetry of the powder diffraction pattern does not allow authors to easily distinguish between fully ordered, fully disordered, or partially ordered anion models. However, Rietveld refinements against both high and medium resolution neutron powder diffraction data clearly favor a statistical distribution of oxide and nitride anions over a single crystallographic site which is contrary to the predictions of previous calculations. The space group is Ia-3 (No. 206), with a=10.13940(7) angstroms at 298 K and Z=16. This symmetry and unit cell are retained at low temperatures (a=10.1250(1) angstroms at 4.5 K). Partial oxidation reveals the existence of a phase with N2 molecules weakly bound and the stoichiometry ZrO2(N2)0.028(1). Authors also report the isostructural Hf oxynitride Hf2ON2 (Ia-3 with a=10.0692(2) angstroms at 298 K as determined using lab XRD data). 24 refs.