Synthesis, Structure and Li Ion Conductivity of Garnet-like Li5+2xLa3Nb2-xSmxO12 (0 ≤ x ≤ 0.7)

Abstract

Here, we report the synthesis, structure and Li ion conductivity of new Sm-doped garnet-type Li5+2xLa3Nb2-xSmxO12 (0 ≤ x ≤ 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, Li5.6La3Nb1.7Sm0.3O12, showed the highest conductivity of ∼10−5 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 Li5+2xLa3Nb2-xSmxO12 (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.