Li-inserted Nb 3O 7F and its thermal decomposition products studied by high-resolution electron microscopy and X-ray powder diffraction

Abstract

Li has been chemically inserted into Nb 3O 7F, obtained by thermal decomposition of NbO 2F. The Li 3 x Nb 3O 7F (0 < x ≤ 1.5) products have been investigated by X-ray powder diffraction and high-resolution electron microscopy techniques. Three different phases, one of orthorhombic, one of triclinic, and one of hexagonal symmetry, could be identified, although none of them were pure. Chemical delithiation was performed by reacting the Li-containing samples with DDQ in acetonitrile. The delithiation results depended on the total Li content of the starting material, but lithium could never be fully extracted. Thermal decomposition of Li 3 x Nb 3O 7F (0 ≤ x ≤ 1.4) was studied by differential scanning calorimetry. The samples were heated to 950 K, and the thermograms revealed that the starting temperature of the decomposition decreased with increasing Li content. The following phases were obtained: LiF, NbO 2, LiNb 3O 8, and LiNbO 3.