Li⁺ conductivity of tungsten bronze Li Sr_1-0.5 Ta₂O₆ studied by neutron diffraction analysis

The crystal structures of tetragonal tungsten bronze, Li Sr_1-0.5 Ta₂O₆ (x = 0.08, 0.17, 0.25) were investigated by neutron diffraction analysis, focusing on the geometry of the oxide framework as well as the Li distribution. The Rietveld refinement and Fourier mapping of nuclear density indicated that Li atoms are distributed in the pentagonal and rectangular channels of the tungsten bronze lattice, which provide 15-fold and 12-fold coordinated cavities, respectively. Those cavities are interconnected to form a three-dimensional network, which can serve as the Li⁺ conduction pathway in Li Sr_1-0.5 Ta₂O₆. It is proposed that the rhombic faces of the 12-coordinated polyhedra (distorted cuboctahedra) act as the bottleneck for long-range Li⁺ migration.