Ba2AlSi5N9—A New Host Lattice for Eu2+-Doped Luminescent Materials Comprising a Nitridoalumosilicate Framework with Corner- and Edge-Sharing Tetrahedra

Ba2AlSi5N9 was synthesized starting from Si3N4, AlN, and Ba in a radio-frequency furnace at temperatures of about 1725 °C. The new nitridoalumosilicate crystallizes in the triclinic space group P1 (no. 1), a = 9.860(1) A, b = 10.320(1) A, c = 10.346(1) A, α = 90.37(2)°, β = 118.43(2)°; γ = 103.69(2)°, Z = 4, R1 = 0.0314. All synthesized crystals were characteristically twinned by reticular pseudomerohedry with twin law (1 0 0, −0.5 −1 0, −1 0 −1). The crystal structure of Ba2AlSi5N9 was determined from single-crystal X-ray diffraction data of a twinned crystal and confirmed by Rietveld refinement both on X-ray and on neutron powder diffraction data. Statistical distribution Si/Al is corroborated by lattice energy calculations (MAPLE). 29Si and 27Al solid-state NMR are in accordance with the crystallographic results. Ba2AlSi5N9 represents a new type of network structure made up of TN4 tetrahedra (T = Si, Al). Highly condensed layers of dreier rings with nitrogen connecting three neighboring tetrahedral cen...