Li-inserted NbO 2F studied by high-resolution electron microscopy and X-ray powder diffraction

Abstract

Chemical insertion of Li in NbO 2F has been performed under various conditions. NbO 2F prepared from Nb-metal and a mixture of HF(aq) and HNO 3(aq) was used as starting material, since NbO 2F made from Nb 2O 5 and HF(aq) was shown to be NbO 2F · HF. The products, with the formula Li x NbO 2F (0 < x ≤ 1.8), have been analyzed for Li content using atomic absorption spectrometry. According to the X-ray powder diffraction results, the Li-incorporated samples with 0.2 < x < 1.3 contained two phases, namely, one of cubic and one of hexagonal symmetry, whereas specimens with x > 1.3 were single phase of a hexagonal structure type. Samples with x = 0.0, 0.3, 0.5, and 1.2 were studied by electron diffraction and high-resolution electron microscopy techniques. Crystals of specimen x = 0.3 were shown to consist predominantly of a cubic phase surrounded by a shell of hexagonal LiNbO 3 structure type, while the crystals of Li 1.2NbO 2F seemed to be built up mainly of the hexagonal phase.