Evaluation on the Effect of Gd-doping for Nb on the Morphology and Ionic Conductivity of Garnet-like Li5La3Nb2O12

There is a great interest in gaining a deeper understanding of the Li ion conductivity of Li stuffed garnets that result from the substitution at either the La or M sites in Li5La3M2O12 (M = Nb, Ta), since these materials can be used as potential electrolytes in all solid state batteries. Here, we investigate the effect of replacing Nb5+ with Gd3+ and stuffing two Li+ per Gd3+ in Li5La3Nb2O12 on the structure and ionic conductivity of the new family of garnet-type compounds with the nominal formula Li5+2xLa3Nb2-xGdxO12 (0 ≤ x ≤ 0.45). The samples were prepared via conventional solid-state synthesis in air at elevated temperatures. Powder X-ray diffraction (PXRD) studies confirmed the formation of the garnet-type structure for Li5+2xLa3Nb2-xGdxO12 (0 ≤ x ≤ 0.45). Elemental mapping obtained using energy dispersive X-ray analysis (EDS) showed no evidence of a secondary phase being formed in Li5+2xLa3Nb2-xGdxO12 (0 ≤ x ≤ 0.45). Archimedes’ density measurements confirmed that the density of the samples with x ≤ 0.25 is not improved. The porosity of the samples with x ≥ 0.3 was found to be in the 8-16 % range Among the samples investigated in this work, the x = 0.45 member of Li5+2xLa3Nb2-xGdxO12 showed the highest ionic conductivity of 1.91 x 10-5 S cm-1 at room temperature, which is an order of magnitude higher than that of the parent compound Li5La3Nb2O12. The activation energy of this material was calculated to be 0.38 eV at 25 - 225 °C and 0.28 eV at 225 - 325 °C. The change in the activation energy at high temperature regime can be explained using the Li-site occupation model in the garnet-type structure.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author