The crystal structure of barium hexaaluminate phase I (barium β-alumina)

Preparation and Crystal Structure Analysis of Magnetoplumbite-Type BaGa12O19

“…Instead, it was found that barium hexaaluminate exists as a two-phase material: Phase I is Ba-poor with respect to BaAl O , and Phase II is relatively Ba-rich. The Phase I material has since been well characterized by single-crystal X-ray diffraction (4,5), and the Phase II structure has been characterized both by highresolution transmission electron microscopy (HRTEM) (6) and from single crystal X-ray studies as the Pb-stabilized form (7).…”

Identification of the Crystallographic Sites of Ir in BaIr0.2FeAl10.8O19 Hexaaluminate

“…41 Refinements of the Al occupancies (Table 3) indicated that Fe ions occupied the symmetric tetrahedral Al(2) sites in the spinel block and the distorted tetrahedral interstitial Al(5) sites in the mirror plane with occupancy of 20.2% and 6.0%, respectively, similar to the distribution of Fe in BF1A-1200 (20.1% and 6.5%). 22,23 In contrast to Fe, Ir ions only occupied the tetrahedral interstitial Al(5) sites in the mirror plane, while Al(1), Al(2), Al(3), and Al(4) sites did not show any significant evidence of Ir substitution.…”

Stabilization mechanism and crystallographic sites of Ru in Fe-promoted barium hexaaluminate under high-temperature condition for N2O decomposition

“…In Bapoor ␤ I -Al 2 O 3 structure (Fig. 6), small fractions of Al 3+ ions shifted from their normal octahedral Al(1) sites in the spinel block to new tetrahedral interstitial Al(5) sites in the mirror plane bridged by interstitial oxygen due to the vacancy of Ba 2+ through a Reidinger defect mechanism [41]. Similar with the distribution of Fe in BF1A-1200 [29], the refinement of our data also revealed that Fe ions in BR0.2F1A-1200 sample occupied both the symmetric tetrahedral Al(2) sites in the spinel block and the distorted tetrahedral interstitial Al(5) sites in the mirror plane (Table 4).…”

“…According to Pauling's electrostatic valence rule [41], the ideal valence of the large cation in the mirror plane required for the stoichiometric Ba-poor ␤ I -Al 2 O 3 structure can be estimated and found to be +1.5, which is lower than the actual charge (+2.0) of large Ba 2+ cation. To maintain electroneutrality with respect to the more positive charge provided by Ba 2+ , a quarter of the Ba 2+ in the mirror plane (Beevers-Ross sites) is replaced by O 2− (Reidinger defects), leading to the shift of small fractions of Al 3+ ions from Al(1) sites to interstitial Al(5) sites (Fig.…”