Phase relation, structure and ionic conductivity of Li7-x-3yAlyLa3Zr2-xTaxO12

• Published in: RSC advances 2016-01, Vol.6 (81), p.78210-78218
• Main Authors: Matsuda, Yasuaki, Itami, Yuya, Hayamizu, Kikuko, Ishigaki, Toru, Matsui, Masaki, Takeda, Yasuo, Yamamoto, Osamu, Imanishi, Nobuyuki
• Format: Article
• Language: eng ; jpn
• Subjects: Atomic structure; Borders; Diffusion; Disorders; Grain boundaries; Ionic conductivity; Lithium; Lithium ions
• ISSN: 2046-2069
• DOI: 10.1039/c6ra13317g

The phase relation, structure and ionic conductivity of garnet-like Li7-x-3yAlyLa3Zr2-xTaxO12 were investigated. The improved sample dissolution process in the ICP measurements enabled the exclusion of the ambiguity of the atomic composition in the samples. The tetragonal phase formed at x = 0-0.375 and the cubic phase appeared with x = 0.4-2.0 in the Li7-xLa3Zr2-xTaxO12 system. In the Al-doped system of Li7-x-3yAlyLa3Zr2-xTaxO12, the tetragonal phase was formed at x + 3y < 0.4. The border between the tetragonal and the cubic phases exists at Li6.6-z/2Alz/2[squ0.4La3Zr1.6+zTa0.4-zO12. The tetragonal/cubic structure change corresponds to the order/disorder of lithium ions and is dependent on the cation content at the lithium sites. The ionic conductivity of the cubic compounds has a positive tendency with respect to the lithium content, whereas that of the tetragonal compounds is opposite. A high total ionic conductivity exceeding 5.0 10-4 S cm-1 at 25 degree C was observed for Al-doped Li6.6-z/2Alz/2La3Zr1.6+zTa0.4-zO12. The highest total conductivity of 1.03 10-3 S cm-1 at 25 degree C with an activation energy of 0.35 eV was obtained at z = 0.275. Nuclear magnetic resonance spectroscopy revealed that Al3+ substitution decreases the diffusion of lithium ions in the structure. The high total conductivity of Al-doped Li6.6-z/2Alz/2La3Zr1.6+zTa0.4-zO12 may be due to the enhancement of lithium diffusion at the grain boundaries.