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

Ta-doped Li7La3Zr2O12 (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·H2O, La2O3, ZrO2 and Ta2O5 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.