Fast Li-Ion-Conducting Garnet-Related Li7-3xFexLa3Zr2O12 with Uncommon I43d Structure

• Published in: Chemistry of materials Vol. 28; no. 16; pp. 5943 - 5951
• Main Authors: Wagner, Reinhard, Redhammer, Guenther J, Rettenwander, Daniel, Tippelt, Gerold, Welzl, Andreas, Taibl, Stefanie, Fleig, Juergen, Franz, Alexandra, Lottermoser, Werner, Amthauer, Georg
• Format: Journal Article
• Language: English
• Published: 28.07.2016
• Subjects: Diffraction; Garnets; Lithium; Oxides; Reduction (electrolytic); Single crystals; Symmetry; X-rays
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.6b02516

Fast Li-ion-conducting Li oxide garnets receive a great deal of attention as they are suitable candidates for solid-state Li electrolytes. It was recently shown that Ga-stabilized Li7La3Zr2O12 crystallizes in the acentric cubic space group I43d. This structure can be derived by a symmetry reduction of the garnet-type Ia3d structure, which is the most commonly found space group of Li oxide garnets and garnets in general. In this study, single-crystal X-ray diffraction confirms the presence of space group I43d also for Li7-3xFexLa3Zr2O12. The crystal structure was characterized by X-ray powder diffraction, single-crystal X-ray diffraction, neutron powder diffraction, and Mosbauer spectroscopy. The crystal-chemical behavior of Fe3+ in Li7La3Zr2O12 is very similar to that of Ga3+. The symmetry reduction seems to be initiated by the ordering of Fe3+ onto the tetrahedral Li1 (12a) site of space group I43d. Electrochemical impedance spectroscopy measurements showed a Li-ion bulk conductivity of up to 1.38 10-3 S cm-1 at room temperature, which is among the highest values reported for this group of materials.