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

Sr10Al6O19 is monoclinic, space group C12/c1, a=34.5823(21) Å, b=7.8460(6) Å, c=15.7485(9) Å, β=103.68(1)°, V=4151.9(7) Å3, 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>2σ(I). The compound is an oligoaluminate containing highly puckered [Al6O19]-groups of corner-sharing tetrahedra; it is the first purely aluminate cluster of this type, but it resembles the [□6O19]-group recently found in α-Sr10□6O19. 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, ABO3, by introducing ordered vacancies into the substructure of the oxygen atoms. The A-sites in Sr10Al6O19 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(Al3/4Sr1/4)(O19/8□5/8).