STRUCTURE STABILIZATION AND IONIC CONDUCTION OF LI-DOPED CATION-DEFICIENT PEROVSKITE SOLID ELECTROLYTES

摘要

Undoped and Li-doped lanthanum titanates were prepared using oxides as the starting materials. Sintered samples were examined by XRD, SEM, EDX and AC impedance spectroscopy. It was observed that the powder mixture of La_2O_3 and TiO_2 could not form a La_(2/3)TiO_3 perovskite when heated at 1350℃ in air. A well-defined perovskite structure was obtained when the same powder mixture was heated in a reducing environment or added with more than 10 mol% of Li. The structure variation of Li-doped lanthanum titanate was rationalized on the basis of defect chemistry. The excess cation vacancies are believed to be the main reason for the instability of La_(2/3)TiO_3. The elimination of cation vacancies and structure stabilization were achieved by either the heat treatment under reducing atmosphere or the addition of Li ions. For conductivity measurements, a maximum conductivity of 2.51 x 10~(-5) S/cm was obtained when Li ions added reached 30 mol%. This result is consistent with the consideration based on the available vacancies and the charge carriers.