Monoclinic superstructure in orthorhombic Ce₁₀W₂₂O₈₁ from transmission electron microscopy

A complex rare-earth tungstate structure, present in a two-phased powder, was solved by electron diffraction, precession and high-resolution electron microscopy. The orthorhombic space group Pbnm and the atomic positions deduced from X-ray diffraction experiments were confirmed for Ce₁₀W₂₂O₈₁. A C2/c monoclinic superstructure, with cell parameters a = 7.8, b = 36.1, c = 22.2 Å and β = 100.2°, was shown and attributed to a partial oxidation of Ce³⁺ leading to interstitial oxygen ions.