X-Ray powder diffraction study of LiLnTiO_4 (Ln chemical bounds La, nd): a lithium-ion conductor

摘要

We report the synthesis, structure and ionic conductivity of new layered perovsikite oxides of the formula LiLnTiO_4 (Ln chemical bounds La, ND). These oxides were synthesizd from their sodium analogues, NaLnTiO_4, by ion-exchange using molten LiNO_3. Determination of crystal structure by Rietveld analysis of owder X-ray diffraction data reveals that LiLnTiO_4 compounds crystallize in a tetragonal structure, P4mm space-group (a chemical bounds 3.7700(2) A, c chemical bounds 12.076 (1) A for La compound; a chemical bounds 3.7465 (3) A, c chemical bounds 11.895(5) A. for Nd compound), related to the parent NaLnSTiO_4. While the Na atoms in NaLnTiO_4 are 9-coordinated as in the K_2NiF_4 structure, the Li atoms in LiLnTiO_4 are 4-coordinated )tetrahedral); other structural features of NaLnTiO_4 are retained in LiLnTiO_4. LiLnTiO_4 oxides show moderate lithium-ion conductivity (s approx = 10~(-4) S.cm~(-1) at 780 deg C) that is higher by about two orders of magnitude than that of Li_2La_2Ti_3O_(10).