A new lithium barium aluminum oxide fluoride, LiBa2AlO3F2

Abstract

Single-crystal grains of a new quinary compound, LiBa2AlO3F2, were obtained from a polycrystalline sample prepared by heating a starting binary oxide and fluoride mixture with a composition richer in Li and Al than the stoichiometric composition at 1023 ​K. Single-crystal X-ray structure analysis revealed that LiBa2AlO3F2 crystallizes in an orthorhombic cell (a ​= ​7.9953 (3) Å, b ​= ​11.7763 (4) Å, c ​= ​5.6090 (2) Å, space group Pbcm). Al-centered O tetrahedra form zigzag chains in the c-axis direction by sharing vertex oxygen atoms. An OF4 four-sided pyramid is formed, and a Li atom is situated in the pyramid and near the F4 basement. A Li-OF4 pyramid layer is formed by sharing F atoms of the pyramid at x ∼0 around the (100) plane. Ba atoms are located between the slab of Al–O4 zigzag chains and the Li–OF4 pyramid layer. Rietveld analysis of the powder X-ray diffraction pattern indicated that a single-phase polycrystalline bulk sample of LiBa2AlO3F2 was synthesized from a starting-materials mixture with the stoichiometric composition. The conductivity measured for the sample prepared at 1173 ​K was 2.6 ​× ​10−9 ​S ​cm−1 ​at 301 ​K and 2.9 ​× ​10−6 ​S ​cm−1 ​at 443 ​K, and the Li+ transport number was 99%. LiBa1.94Eu0.06AlO3F2 was synthesized by partial substitution of Eu2+ for Ba2+. A broad emission spectrum with a peak at 610 ​nm and a full-width at half-maximum of 170 ​nm was recorded for this sample under ultraviolet-light excitation at a wavelength of 330 ​nm.