MgO or Al2O3 crucible: Which is better for the preparation of LLZ-based solid electrolytes?

Lithium lanthanum zirconate (Li 7 La 3 Zr 2 O 12 , LLZ) solid electrolytes were usually prepared by using Al 2 O 3 crucibles and/or Al 3+ dopants in order to stablize the formation of cubic garnet phase. In this work, we argue that Al-free MgO crucible could be better for the preparation of LLZ-based solid electrolytes through a detailed comparison of LLZ-Ga 0.2 samples prepared respectively by using MgO and Al 2 O 3 crucibles. The solid-state reaction method was firstly used to prepare Li 7-3 x Ga x La 3 Zr 2 O 12 ( x  = 0–0.4) pellets by using Al-free MgO crucibles, which were sintered at 1100 °C for 12 h. The highly conductive cubic phase was obtained at Ga 3+ doping content as low as x  = 0.05 and the highest room-temperature conductivity was obtained at x  = 0.2. Al 2 O 3 crucible was then used to prepare the LLZ-Ga 0.2 pellet for comparing the influence of these two different crucibles. The results show that a higher lattice parameter ( a  = 12.9762 (8) Å), a higher relative density (95.5%) and a higher room-temperature ionic conductivity (1.352 (3) mS/cm) were achieved by using the MgO crucible.