| Summary: | Garnet-type Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> (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<sub>7-x</sub>La<sub>3</sub>Zr<sub>2-x</sub>Nb<sub>x</sub>O<sub>12</sub> ceramics, is particularly important. In this study, Li<sub>7-x</sub>La<sub>3</sub>Zr<sub>2-x</sub>Nb<sub>x</sub>O<sub>12</sub> (LLZN<sub>x</sub>O, 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<sub>x</sub>O (x = 0, 0.2, 0.4, 0.6) ceramics was investigated. Due to the more contractive Nb-O bonds in LLZN<sub>x</sub>O ceramics, the cubic structures are much easier to form and stabilize, which could induce the decreased preparation time. High-performance garnet LLZN<sub>x</sub>O 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<sup>−4</sup> S·cm<sup>−1</sup> 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.
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