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

Abstract Lithium lanthanum zirconate (Li7La3Zr2O12, LLZ) solid electrolytes were usually prepared by using Al2O3 crucibles and/or Al3+ 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-Ga0.2 samples prepared respectively by using MgO and Al2O3 crucibles. The solid-state reaction method was firstly used to prepare Li7-3xGaxLa3Zr2O12 (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 Ga3+ doping content as low as x = 0.05 and the highest room-temperature conductivity was obtained at x = 0.2. Al2O3 crucible was then used to prepare the LLZ-Ga0.2 pellet for comparing the influence of these two different crucibles. The results show that a higher lattice parameter (a = 12.9762 (8) A), 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.