Tungsten bronze Li+ conductor Li Sr1−0.5Ta2O6 (0 < x ≤ 0.31) prepared by solid state ion exchange

The lithiation of tungsten bronze oxide β-SrTa 2 O 6 was accomplished by the solid state ion exchange of Sr 2+ → 2Li + , which led to a solid solution of Li x Sr 1−0.5 x Ta 2 O 6 ( x = 0–0.31). For the above conversion, β-SrTa 2 O 6 was reacted with various amounts of Li 2 CO 3 at 600 &#176;C in air. With increasing x in Li x Sr 1−0.5 x Ta 2 O 6 , 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 Li x Sr 1−0.5 x Ta 2 O 6 phases with x = 0.17 and 0.25 were formed from columnar bundles aligned along the c -axis. Solid state 7 Li nuclear magnetic resonance (NMR) spectroscopy revealed the presence of two different Li environments in Li x Sr 1−0.5 x Ta 2 O 6 , and their respective populations. The ionic conductivity of Li x Sr 1−0.5 x Ta 2 O 6 was measured by ac impedance spectroscopy as functions of the temperature and composition x . Regardless of the composition, the conductivity of Li x Sr 1−0.5 x Ta 2 O 6 displayed an Arrhenius type temperature dependence, and the highest Li + conductivity was found from x ≈ 0.17. At temperatures between 75 and 268 &#176;C, the Li + ionic conductivity of Li 0.17 Sr 0.92 Ta 2 O 6 increased from 10 −8.8 S/cm to 10 −5.0 S/cm with an activation energy of 0.74 eV.