Perovskite-related structures of Ba 2 YAlO 5 and the β and α phases of Ba 6 Y 2 Al 4 O 15 containing AlO 4 tetrahedra.

Single crystals of Ba 2 YAlO 5 and of the α and β phases of Ba 6 Y 2 Al 4 O 15 suitable for X-ray structure analysis were obtained via grain growth of polycrystalline samples prepared by solid-state reactions. Ba 2 YAlO 5 was found to have a monoclinic crystal structure, with lattice parameters a = 7.2333 (7), b = 6.0254 (5), c = 7.4294 (7) Å and β = 117.249 (3)°, and to belong to the space group P2 1 /m, while α-Ba 6 Y 2 Al 4 O 15 was determined to be monoclinic, with a = 5.9019 (2), b = 7.8744 (3), c = 9.6538 (3) Å and β = 107.7940 (10)°, and the space group Pm, and β-Ba 6 Y 2 Al 4 O 15 was found to be monoclinic, with a = 7.8310 (2), b = 5.8990 (2), c = 18.3344 (6) Å and β = 91.6065 (11)°, and the space group P2/c. In each of these compounds, BO 6 octahedra in ABO 3 perovskite-type structures were replaced by AlO 4 tetrahedra and YO 6 octahedra. Polycrystalline samples in which some Y atoms were replaced with Eu exhibited orange-red luminescence in the range 580-730 nm in response to exposure to radiation having a wavelength of approximately 250 nm.