Effect of Sintering Process on Ionic Conductivity of Li_7-xLa₃Zr_2-xNb_xO₁₂ (x = 0, 0.2, 0.4, 0.6) Solid Electrolytes

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is considered as a promising solid electrolyte. Nb-doped LLZO ceramics exhibit significantly improved ion conductivity. However, how to prepare the Nb-doped LLZO ceramics in a simple and economical way, meanwhile to investigate the relationship between process conditions and properties in Li_7-xLa₃Zr_2-xNb_xO₁₂ ceramics, is particularly important. In this study, Li_7-xLa₃Zr_2-xNb_xO₁₂ (LLZN_xO, x = 0, 0.2, 0.4, 0.6) ceramics were prepared by conventional solid-state reaction. The effect of sintering process on the structure, microstructure, and ionic conductivity of LLZN_xO (x = 0, 0.2, 0.4, 0.6) ceramics was investigated. Due to the more contractive Nb-O bonds in LLZN_xO ceramics, the cubic structures are much easier to form and stabilize, which could induce the decreased preparation time. High-performance garnet LLZN_xO ceramics can be obtained by optimizing the sintering process with lower calcining temperature and shorter holding time. The garnet samples with x = 0.4 calcined at 850 °C for 10 h and sintered at 1250 °C for 4 h exhibit the highest ionic conductivity of 3.86 × 10^-4 S·cm^-1 at room temperature and an activation energy of 0.32 eV, which can be correlated to the highest relative density of 96.1%, and good crystallinity of the grains.