Wide range lattice parameter control by aliovalent substitution to the rare-earth site in cubic garnet Li6.75(La1-xSmx)3Zr1.75Ta0.25O12

Garnet-type Li-ion conductor Li-6.75(La1-xSmx)(3)Zr1.75Ta0.25O12 powders were synthesized with 0 <= x <= 1 using solid-state reaction method. Almost single-phased garnet phase was obtained by synthesis at 900 degrees C for all Sm contents. The lattice parameters decrease linearly, concomitantly with increasing Sm content, following Vegard's law. Results of X-ray diffraction and Raman spectroscopy show that Sm is substituted to the rare-earth element site and that the cubic structure of garnet is stable as a main phase at room temperature. Therefore, this study demonstrates that Sm substitution to La site in the garnet-type Li-ion conductor provides continuous lattice parameter control in a wide range up to alpha = 1.27170(8) nm. It is noteworthy that the wavenumber shifts of Raman mode related to the four-coordinated Li-O bond are observed only slightly in spite of the large lattice constriction and clear observation of peak-top shifts of other cation-oxygen modes, implying that Li-ion conductivity would be less affected by aliovalent substitution to the rare-earth site. (C) 2020 The Ceramic Society of Japan. All rights reserved.