Crystal structure of distorted fluorite-type SrU2O6 with pentavalent uranium

Electron paramagnetic resonance absorption (EPR) of SrU2O6, in which the strontium and uranium atoms randomly occupy the metal sites of the fluorite-type crystal, showed a slightly anisotropic signal. In relation with this anomalous signal, the crystal structure of SrU2O6 has been analyzed by powder X-ray diffraction and Rietveld refinement. The sample has been found to consist of two phases with 73% and 27% in mass percent. The major phase crystallized in nearly cubic symmetry with slight rhombohedral distortion (a=3.8642 Angstrom and alpha=60.096 degrees), whereas the other showed a significant rhombohedral distortion from cubic symmetry, i.e. a=3.8334 Angstrom and alpha=62.024 degrees. Consequently, the existence of these two phases has been considered to be one of the possible origins which introduce the observed anisotropic signal of EPR. (C) 1998 Elsevier Science S.A.