Reactive sintering of garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) from pyrochlore precursors prepared using a non-aqueous sol–gel method

Garnet-type solid-state electrolytes such as Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) are promising ceramic electrolytes for all-solid-state batteries because of their high (electro)chemical stability and ionic conductivity. LLZTO is typically synthesized from oxide precursors via solid-state reaction, but use of other precursors such as pyrochlores has also received recent interest. Here, a Ta-doped pyrochlore was prepared using non-aqueous sol–gel methods to serve as precursor for LLZTO. The dense LLZTO ceramic was directly obtained via a reactive sintering method with ionic conductivity ~ 0.4 mS/cm, which is comparable to LLZTO prepared by solid-state reaction, using only 2 h sintering at 1100 ℃. Investigation of the synthesis parameters shows that liquid phase sintering is important for achieving high pellet densities and phase purity. The grain size of LLZTO is less than 2 μm, indicating that fine-grained garnet ceramics are accessible with this approach. This work reveals an alternate method for the synthesis and processing of LLZTO materials.