Synthesis of lithium garnets from La2Zr2O7 pyrochlore

• Lithium garnets were prepared using La2Zr2O7 (LZ) pyrochlore.
• Lithium garnets prepared using LZ stabilized into tetragonal phase at 950 °C.
• Lithium garnets prepared using LZ stabilized into cubic phase only at 1200 °C.
• Al doped Li7La3Zr2O12 prepared by solid state stabilizes in cubic phase at 950 °C.

An attempt has been made in this work to prepare lithium garnets from La2Zr2O7 (LZ) pyrochlore. Systematic investigation has been carried out on direct solid-state reaction of LZ pyrochlore with lithium–lanthanum oxides Li7LaO5 (LL) and lithium–aluminum–lanthanum oxides Li6.28Al0.24LaO5 (LAL) to understand the role of LZ pyrochlore in the formation of tetragonal and high Li+ conductive cubic phase lithium garnets. Structural studies indicated the stabilization of LLZ (using LZ + LL) and Li6.28Al0.24La3Zr2O12 (using LZ + LAL) in tetragonal phase at 950 °C and into high Li+ conductive cubic phase only at the sintering temperature of 1200 °C. However, Li6.28Al0.24La3Zr2O12 prepared from the reactants LiOH ∙ H2O, La2O3, Al2O3 and ZrO2 stabilized into high Li+ conductive cubic phase at 950 °C. Among the investigated samples, the lithium deficient and Al doped LALZ-cs sintered at 1200 °C exhibits maximized relative density (93%) and total (bulk + grain-boundary) Li+ conductivity of 4.43 × 10− 4 S cm− 1 at 30 °C with minimum activation energy of 0.37 eV.

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