Spark plasma sintering plus heat-treatment of Ta-doped Li₇La₃Zr₂O₁₂ solid electrolyte and its ionic conductivity

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Ta-doped Li 7 La 3 Zr 2 O 12 (Ta-LLZO) solid electrolyte ceramics were synthesized by solid-state sintering, spark plasma sintering (SPS) and SPS plus heat-treatment (two-step method) using LiOH·H 2 O, La 2 O 3 , ZrO 2 and Ta 2 O 5 as the raw materials. The Ta-LLZO samples prepared from these three routes are all in cubic phase structure. However, the solid-state method results in Ta-LLZO samples with different particle sizes and porous morphology, while the samples prepared by SPS route contain fewer internal voids and smaller particle size. The two-step method not only retains the high compactness of SPS samples, but also the increment of grain size. The SEM results demonstrate that Ta-LLZO sintered by the two-step method shows optimal electrical properties. And the total ionic conductivity is 4.6 × 10 −3 S cm −1 at 150 °C and the activation energy is calculated to be 0.38 eV.