Tungsten bronze Li+ conductor Li^sub x^Sr^sub 1-0.5x^Ta^sub 2^O^sub 6^ (0 < x = 0.31) prepared by solid state ion exchange

• Published in: Journal of alloys and compounds Vol. 726; p. 913
• Main Authors: Han, Hyeon-Dong, Park, Chee-Sung, Min, Bong-Ki, Paik, Younkee, Jung, Woong, Kim, Young-Il
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier BV 05.12.2017
• Subjects: Conductors; Electron microscopy; Ion currents; Ion exchange; NMR; Nuclear magnetic resonance; Scanning electron microscopy; Solid state; Temperature dependence; Transmission electron microscopy; Tungsten bronze
• ISSN: 0925-8388; 1873-4669

The lithiation of tungsten bronze oxide β-SrTa2O6 was accomplished by the solid state ion exchange of Sr2+ → 2Li+, which led to a solid solution of LixSr1-0.5xTa2O6 (x = 0-0.31). For the above conversion, β-SrTa2O6 was reacted with various amounts of Li2CO3 at 600 °C in air. With increasing x in LixSr1-0.5xTa2O6, an orthorhombic-to-tetragonal symmetry transition was observed along with a gradual decrease in lattice volume. As observed from scanning electron microscopy and transmission electron microscopy, the grains of LixSr1-0.5xTa2O6 phases with x = 0.17 and 0.25 were formed from columnar bundles aligned along the c-axis. Solid state 7Li nuclear magnetic resonance (NMR) spectroscopy revealed the presence of two different Li environments in LixSr1-0.5xTa2O6, and their respective populations. The ionic conductivity of LixSr1-0.5xTa2O6 was measured by ac impedance spectroscopy as functions of the temperature and composition x. Regardless of the composition, the conductivity of LixSr1-0.5xTa2O6 displayed an Arrhenius type temperature dependence, and the highest Li+ conductivity was found from x ≈ 0.17. At temperatures between 75 and 268 °C, the Li+ ionic conductivity of Li0.17Sr0.92Ta2O6 increased from 10-8.8 S/cm to 10-5.0 S/cm with an activation energy of 0.74 eV.