Synthesis, structure and Li Ion conductivity of garnet-like Li5₊2_xLa3Nb2-_xSm_xO₁₂ (0 ≤ × ≤ 0.7)

Here, we report the synthesis, structure and Li ion conductivity of new Sm-doped garnet-type Li₅₊₂xLa₃Nb_2-xSm_xO₁₂ (0 ≤ × ≤ 0.7). Powder X-ray diffraction showed the formation of cubic garnet structure up to x = 0.3. Above x = 0.3 impurity phases were observed, due to LiNbO₃ (the joint committee on powder diffraction standards (JCPDS) card No. 01-074-2239), LiSmO₂ (JCPDS Card No. 01-073-1061) and Sm₂O₃ (JCPDS Card No. 15-0813). The cubic cell constant increased from 12.774(2) Å (x = 0) to 12.851(2) Å (x = 0.3). Scanning electron microscopy showed that Sm-doping results in an increase in density of the samples, as a result of improved particle-to-particle contact. Among the samples investigated, Li_5.6La₃Nb_1.7Sm_0.3O₁₂, showed the highest conductivity of ∼10 S cm^-1 at 24°C which is an order of magnitude higher than that of the parent compound, Li₅La₃Nb₂O₁₂. The activation energy in the temperature range 25-225°C decreased with an increase in Sm-dopant in Li_5+2xLa₃Nb_2-xSm_xO₁₂ (0.45 eV for x = 0.05 to 0.38 eV for x = 0.3). Fourier transform infrared spectroscopy studies revealed the presence of Li₂CO₃ in both aged and fresh samples, while thermogravimetric analysis results showed that fresh samples exhibit a lower weight loss compared to the aged samples.