The crystallographic structures of several transition aluminas possessing a face-centered cubic packing of O anions could be considered as deriving from that of a non-stoichiometric spinel. However, these were not known in detail due to the poor crystallinity of most samples studied by X-ray or electron diffraction. Relatively large crystals were produced in the case of non-stoichiometric spinels in alumina-rich or gallia-rich parts of these systems. Detailed studies of their diffraction patterns showed that all of these phases contained periodic antiphase boundary structures that were based upon the spinel structure. In the case of the so-called d-transition aluminas, various structural models had been proposed. Here, attention was focussed on striking similarities between their diffraction patterns and those of several metastable periodic antiphase boundary aluminate structures. This made it possible to show that at least 3 distinct periodic antiphase boundary structures had to be taken into account in the case of d-transition aluminas. The antiphase boundary planes were either {100} or {110}, whereas antiphase boundary vectors were either 1/2 or 1/4 when referred to the spinel structure. Neighboring octahedral and tetrahedral incompatible sites were observed in the vicinity of each antiphase boundary, and cation vacancies were shown to occupy these octahedral sites.

Periodic Antiphase Boundary Spinel-Based Structures in Aluminates, Gallates, Aluminium Oxynitrides and Transition Aluminas. A.Lefebvre, D.Jacob, Y.Androussi: Philosophical Magazine, 2005, 85[20], 2211-25