Li2 Ba4 Al2 Ta2 N8 O, the First Barium Nitridoalumotantalate with BCT-Zeolite Type Structure

Abstract

Single-crystals of Li₂ Ba₄ Al₂ Ta₂ N₈ O:Eu²⁺ were synthesized from Ba₃ N₂ , Al₂ O₃ , Li₃ N, Eu₂ O₃ , and lithium metal by a high-temperature solid-state reaction in a weld shut tantalum ampule. The crystal structure of Li₂ Ba₄ Al₂ Ta₂ N₈ O was determined by single-crystal X-ray diffraction and it crystallizes in the orthorhombic space group Pnnm (no. 58) with the lattice parameters a=1006.71(3), b=1026.58(3), c=607.10(2) pm, and a volume of V=0.62742(3) nm³ . The compound is built up from AlN₄ and TaN₄ tetrahedra, which form a three-dimensional network corresponding to the BCT-zeolite type structure. Li₂ Ba₄ Al₂ Ta₂ N₈ O is homeotypic to Li₂ Sr₄ Si₄ N₈ O and Li₂ Sr₄ Al₂ Ta₂ N₈ O but, additionally, it could be successfully doped with the activator ion Eu²⁺ and hence features an experimental observed overall emission at λ_max =565 nm (fwhm=89 nm) consisting of a superposition of two adjusted emission bands at λ_max =557 nm (fwhm=69 nm) and at λ_max =604 nm (fwhm=102 nm).

Keywords: crystal structure; europium; group-subgroup relation; high-temperature solid-state reaction; nitridoalumotantalate phosphor.