Synthesis, crystal structure, and ionic conductivity of novel Ruddlesden-Popper related phases, Li4Sr3Nb5.77Fe0.23O19.77 and Li4Sr3Nb6O20

The authors have synthesized two new lithium-containing oxides which are related to Ruddlesden-Popper phases, Li4Sr3Nb5.77Fe0.23O19.77 and Li4Sr3Nb6O20, with partial occupancy of the 12-coordinated sites by Sr, for the first time by direct solid-state reaction. While the single crystal and powder X-ray diffraction data indicate that these oxides crystallize in tetragonal cells (space group I4/mmm; a = 3.9585(2) angstrom, c = 25.915(3) angstrom and a = 3.953(2) angstrom, c = 26.041(5) angstrom for the respective oxides), the electron diffraction of some of the crystallites shows supercell reflections with a ∼ √2ap, c ∼ 25.9 angstrom, probably indicating a twisting of the NbO6 octahedra in the ab-plane. Although, these oxides show no significant lithium ionic conduction at room temperature, they show distinct conductivity values at elevated temperatures