The Li0.33La0.55TiO3 solid electrolyte had a maximum grain ionic conductivity of 1.13 x 10−3S/cm among the Li3xLa2/3−xTiO3 oxides (0.21 ≤ 3x ≤ 0.50), but the total ionic conductivity of its polycrystalline phase was not the highest. Owing to the grain-boundary resistances controlling the total resistances of bulk samples, an excellent solid electrolyte was mainly characterized by the grain-boundary resistances. With regard to the role of Li ions, the substitution of La3+ ions by the Li+ ions weakens the strength of inter-ionic forces, leading to the decrease in the sintering temperature. The presence of La3+/Li+-site vacancies promoted the densification and grain growth and further results in rapid decreased in porosity and grain-boundary resistances. Li0.21La0.60TiO3 with a larger amount of La3+/Li+-site vacancies could therefore exhibited the highest total ionic conductivity through rapidly decreasing its grain-boundary resistances by changing its microstructure, and it becomes a better polycrystalline solid electrolyte than Li0.33La0.55TiO3 in the Li3xLa2/3−xTiO3 system studied, in spite of its lower grain ionic conductivity.

Roles of Lithium Ions and La/Li-Site Vacancies in Sinterability and Total Ionic Conduction Properties of Polycrystalline Li3xLa2/3−xTiO3 Solid Electrolytes (0.21≤3x≤0.50). K.Y.Yang, J.W.Wang, K.Z.Fung: Journal of Alloys and Compounds, 2008, 458[1-2], 415-24