Electron diffraction and microscope studies of zirconium oxides stabilized by several metal oxides

Crystal structures of CaO-stabilized zirconium oxide (CSZ) and Tb4O7-stabilized zirconium oxide (TSZ) were investigated by electron diffraction and electron microscopy. Superlattice spots were observed at the Bragg-reflection positions with even-odd mixed indices of the fluorite-type lattice for CSZ containing 10 mol% CaO and TSZ containing 10 mol% Tb2O3.5. Circular diffuse intensity contours were found for CSZ containing 19 mol% CaO and TSZ containing 40 mol% Tb2O3.5. The diffuse contours, which were studied in detail, were ascribed to a circular split of the ½ ½ ½ superlattice reflection into the plane bisecting perpendicularly the 111 reciprocal-lattice vector G111 of the fluorite structure. The diameter D of the diffuse circles was ~0.24|G_{11\bar 2}| for CSZ and ~0.12|G_{11\bar 2}| for TSZ. The values of D/|G_{11\bar 2}| for CSZ and TSZ, together with that (~ 0.18) for Y2O3-stabilized zirconium oxide (YSZ), showed a monotonic increase against the local strain defined by |rH − rG|/rH (rH and rG are the ionic radii for the host and guest cations, respectively). The origin of circular diffuse contours was attributed to the antiphase domains of an ordered structure, whose boundaries are various planes belonging to the [111] zone axis, and the mean domain-size is strongly correlated with the local strain. The [1{\bar 1}0] high-resolution electron-microscope images of TSZ revealed the presence of antiphase microdomains, whose size agrees well with the inverse of the diameter of the diffuse circles.