Ba₄Al₇Li_28.08O_26.92N_1.08, the Barium Oxonitridolithoaluminate with a Highly Condensed LiO₄ Tetrahedra Framework

The new compound Ba₄Al₇Li_28.08O_26.92N_1.08 consists of AlO₄/AlO₃N tetrahedra, 10-fold coordinated Ba²⁺ cations, and a highly condensed edge- and corner-sharing LiO₄ tetrahedra framework, which leads to a degree of condensation greater than 1. The first barium oxonitridolithoaluminate was synthesized by a high-temperature solid-state reaction in a weld-shut tantalum ampoule and the crystal structure has been determined by single-crystal X-ray diffraction. Ba₄Al₇Li_28.08O_26.92N_1.08 crystallizes in the monoclinic space group P2₁/m (no. 11) with the lattice parameters a = 1052.41(3), b = 615.93(2), c = 1088.45(4) pm, β = 98.86(1)°, and a volume of V = 0.69712(4) nm³. In addition, Ba₄Al₇Li_28.08O_26.92N_1.08 doped with the activator ion Eu²⁺, exhibits a broad band emission with a maximum at λ_max = 524 nm (2.34 eV) with a fwhm of 112 nm (4373 cm^–1/0.54 eV), which can be described by a superposition of two adjusted emission bands at λ_max = 515 nm (2.41 eV) with a fwhm of 70 nm (2704 cm^–1/0.34 eV), and at λ_max = 574 nm (2.18 eV) with a fwhm of 127 nm (4127 cm^–1/0.51 eV).