Synthesis, crystal structure, and lithium ion conductivity of Li_2.10Sn_0.90O_2.85

A white bulk sample of Li_2.10Sn_0.90O_2.85 was prepared by heating a compact pellet of a Li₂O and SnO₂ powder mixture with a molar ratio of 1.10:0.95 at 1000 °C for 6 h in Ar and consisted of colorless transparent crystal grains with sizes in the range of 20–80 μm. X-ray diffraction (XRD) reflections from a single crystal taken from the grains were indexed with C-centered monoclinic cell parameters (a = 5.29120(10) Å, b = 9.2033(2) Å, c = 10.0676(2) Å, β = 100.5030(10)°). The crystal structure was determined with the space group C2/c (No. 15) using Li₂SnO₃ as a starting model. The final structure refinement was performed by partial substitution of Li⁺ for Sn⁴⁺ and the introduction of O²⁻ defects with a formula of Li₂(Li_0.10Sn_0.90)O_2.85. Interstitial sites and continuous disordered distribution of Li⁺ ions were depicted in a differential Fourier synthesis map and an electron density distribution (EDD) map by the maximum entropy method (MEM). The disordered Li⁺ distribution was also revealed as broad peaks by ⁶Li magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The Li⁺ conductivity of Li_2.10Sn_0.90O_2.85 measured at 25 °C was 1.0 × 10⁻⁶ S·cm⁻¹, which was 10⁵ times greater than that of Li₂SnO₃.