1e:T431,X‐ray absorption spectra at Zr‐ K , Ce‐L 111 and Ge‐ K edges in ZrO 2 –CeO 2 and ZrO 2 –GeO 2 solid solutions have been measured at 10 K. Both Ce and Ge substitute for Zr in the cation network, but CeO 8 and GeO 4 polyhedra are maintained around the dopants. The oversized CeO 8 is compressed to a Ce–O distance of 2.30 Å, which is smaller than the 2.35 Å seen in fluorite‐type CeO 2 . Meanwhile, the distortion of the Zr‐cation network is increased and the tetragonality is reduced. The undersized Ge has a Ge–O distance of 1.80 Å, which is much shorter than the Zr–O, distance of 2.10 Å. A strong tendency for Ge–Zr ordering in tetragonal solid solutions into locally scheelite‐like clusters, even within the solubility limit, is observed. This results in an increase in the tetragonality and a decrease in the distortion of the cation network. Despite the opposite effects on tetragonality, both Ce and Ge doping can stabilize tetragonal zirconia albeit via different mechanisms. The structural origin of the cubic phase is also elucidated.1f:T49b,Local atomic structures of Zr and dopant cations in zirconia solid solutions with Fe 2 O 3 , Ga 2 O 3 , Y 2 O 3 , and Gd 2 O 3 have been determined. The Zr ions in both partially stabilized tetragonal and fully stabilized cubic zirconia have their own characteristic structures which are dopant‐independent. The dopant cations substitute for Zr ions despite severe local distortions necessitated by the large difference in dopant–O distance ana Zr─O distance. Dopant ionic size determines the preferred locations of oxygen vacancies. Vacancies introduced by oversized dopants (Y and Gd) are located as nearest neighbors to Zr atoms, leaving 8‐fold oxygen coordination to dopant cations. Undersized dopants (Fe and Ga) compete with Zr ions for the oxygen vacancies in zirconia, resulting in 6‐fold oxygen coordination and a large disturbance to the surrounding next nearest neighbors. Since oxygen vacancies associated with Zr can provide stability for tetragonal and cubic zirconia, these results suggest an explanation for the observation that oversized trivalent dopants are more effective than undersized trivalent dopants in stabilizing cubic and tetragonal phases.20:T542,Selected mixtures in 69 binary systems involving Al₂O₃, Ga₂O₃, Cr₂O₃, Fe₂O₃, Sc₂O₃, In₂O₃, Y₂O₃, and the rare earth oxides were studied by X-ray diffraction techniques after heat treatment at various temperatures. A plot of the radii of the A⁺³ cations versus the radii of B⁺³ cations shows the regions of stability for the different structure types found for the double oxides of the trivalent cations. The following structure types were encountered: A, B, and C-type rare earth oxide; corundum, beta gallia; kappa alumina; garnet; perovskite; and several types which could not be definitely related to known structures. The majority of A⁺³B⁺³O₃ compounds have the perovskite structure. Several phases, including (1-x)Fe₂O₃·xAl₂O_{3 ss} and (1-x)Fe₂O₃·Ga₂O_{3 ss}, appear to have structures similar to kappa alumina. Solid solution definitely occurs in many of the garnet type compounds which contain gallia. Based on the data collected in this survey, the subsolidus phase equilibria relationships of 79 binary systems were drawn.

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