Etude comparative des structures des alumines β stoechiometrique et non stoechiometrique: Etude par diffraction des rayons X (I)

The average structures of non-stoichiometric β_AgNS 11 Al₂O₃-1.25(Ag₂O) and stoichiometricβ_AgS 11 Al₂O₃-0.95 Ag₂O β alumina are determined by X-ray diffraction techniques (R factors 4 and 5% respectively). In both compounds Ag⁺ ions are localized on two off-centers Beevers-Ross positions (BRD) very close to one another and with almost equal occupation factors. The evolution from β_AgNS to /gbS occurs through the decrease of the occupation factor of the anti-Beevers-Ross site and the disappearance of the Frenkel defect. A long range ordered superstructure in β_AgS with the lattice constants a√(3)?a√(3)?c (P6₃/m is observed at room temperature and found to arise from the in layer Ag and O ions. The BRD and Oxygen (5) ions are ordered on off-centered positions around an empty aBR site. The complementary structure reflections are interpreted in a twinned model with two types of domains, for the in layer ions.