Synthesis and crystal structure of Sr10Al6O19: a derivative of the perovskite structure type in the system SrO–Al2O3

Abstract Sr 10 Al 6 O 19 is monoclinic, space group C 12/ c 1, a =34.5823(21) A, b =7.8460(6) A, c =15.7485(9) A, β =103.68(1)°, V =4151.9(7) A 3 , Z =8. The structure has been solved from a single crystal diffraction dataset by direct methods and subsequently refined by a full-matrix least-squares process to a residual index of R (| F |)=0.038 for 2537 observed reflections with I >2 σ ( I ). The compound is an oligoaluminate containing highly puckered [Al 6 O 19 ]-groups of corner-sharing tetrahedra; it is the first purely aluminate cluster of this type, but it resembles the [□ 6 O 19 ]-group recently found in α-Sr 10 □ 6 O 19 . Linkage between the hexamers is provided by 11 crystallographically different strontium atoms located in planes parallel (1 0 0). They are coordinated by six–eight next oxygen neighbours. The structure can be derived from perovskite, ABO 3 , by introducing ordered vacancies into the substructure of the oxygen atoms. The A-sites in Sr 10 Al 6 O 19 are exclusively occupied by Sr atoms, whereas strontium and aluminum atoms reside on the B-positions in the ratio 1:3. The relationship with perovskite can be expressed in the crystal chemical formula Sr(Al 3/4 Sr 1/4 )(O 19/8 □ 5/8 ).