Low temperature, fast synthesis and ionic conductivity of Li₆MLa₂Nb₂O₁₂ (M = Ca, Sr, Ba) garnets

In this paper, we report low temperature, fast synthesis of Li₆MLa₂Nb₂O₁₂ (M = Ca, Sr, Ba) with the cubic garnet structure by sol–gel process. The optimized synthesis condition is 775 °C for 6 h with 10% excess lithium salt. The calcination temperature is nearly 125 °C lower than that in the solid state reaction, and the calcination time(~6 h) is shorter than in the solid state reaction(~24 h). Qualitative phase analysis by X-ray powder diffraction patterns combined with the Rietveld method reveals garnet type compounds as major phases. The cubic lattice parameter is found to increase with increasing size of the alkaline earth ions under the same preparation conditions. The density was found to be increasing with increasing ionic radius of the alkaline earth elements. In comparison, the ionic conductivity decreases with decreasing ionic radius of the alkaline earth elements. Among the compounds, the Li₆BaLa₂Nb₂O₁₂ exhibits the highest ionic conductivity of 1.2 × 10⁻⁵ S cm⁻¹ at room temperature.