Abstract
Cubic zirconia in arc-melted ZrO2–CeO2 exhibits extra reflections of ½(odd odd odd) type in X-ray or electron diffraction patterns, which are forbidden for the ideal fluorite structure. The extra reflections are explained in terms of a regular displacement of oxygen ions in the ⟨111⟩ directions. Domain structures characterized by curved boundaries with antiphase-domain-boundary-like contrast appear in dark-field images taken using the extra reflections. The domain structure is associated with the oxygen ions' displacement, and the domain boundary is regarded as a ∏ boundary whose displacement vector is (a/2)⟨110⟩.