X-ray powder diffraction study of LiLnTiO₄ (Ln = La, Nd): a new lithium-ion conductor

Abstract

We report the synthesis, structure and ionic conductivity of new layered perovskite oxides of the formula LiLnTiO₄ (Ln=La, Nd). These oxides were synthesized from their sodium analogues, NaLnTiO₄, by ion-exchange using molten LiNO₃. Determination of crystal structure by Rietveld analysis of powder X-ray diffraction data reveals that LiLnTiO₄ compounds crystallize in a tetragonal structure, P4/nmm space-group (a=3.7700(2) Å, c=12.076(1) Å for La compound; a=3.7465(3) Å, c=11.895(5) Å for Nd compound), related to the parent NaLnTiO₄. While the Na atoms in NaLnTiO₄ are 9-coordinated as in the K₂NiF₄ structure, the Li atoms in LiLnTiO₄ are 4-coordinated (tetrahedral); other structural features of NaLnTiO₄ are retained in LiLnTiO₄. LiLnTiO₄ oxides show moderate lithium-ion conductivity (s = 10^-4-10^-5 S.cm^-1 at 780°C) that is higher by about two orders of magnitude than that of Li₂La₂Ti₃O₁₀.