Hirotoshi Yamada

Li-intercalated ReO3-type solid solutions in the Nb2O5–WO3 system

ReO{sub 3}-type solid solutions in the Nb{sub 2}O{sub 5}-WO{sub 3} system were synthesized by heat treatment of niobium-doped peroxo-polytungustic acids at relatively low temperature ranging from 600 to 1,000 C. The resultants cooled from 1,000 C to room temperature were monoclinic in the composition range 0 {le} x {le} 0.05 [x = Nb/(Nb + W)] and tetragonal for 0.05 0.25. The Rietveld structural refinement showed that a tetragonal compound at x = 0.118 takes a distorted ReO{sub 3}-type structure [a = 5.2961(5), c = 3.8534(4) {angstrom} at 25 C], analogous to the high-temperature form of WO{sub 3}, in which some oxygens are vacant and the metallic elements are distributed at random. Chemical insertion of lithium into such a tetragonal host framework was carried out using a 0.016 M n-butyl lithium/n-hexane solution at 25 C. It accommodated Li up to y = 1.0 in terms of Li{sub y}Nb{sub x}W{sub 1{minus}x}O{sub 3{minus}x/2} (x = 0.118), but the host structure remained tetragonal in the whole range of y.

Lithium insertion to ReO3-type metastable phase in the Nb2O5-WO3 system

Lithium insertion to distorted ReO3-type metastable solid solution NbxW1−xO3−x/2 (0≤x<0.25) has been studied by chemical and electrochemical methods. In the course of lithium insertion into tetragonal compounds, transition to a cubic phase was found to occur in the region where values of y (in LiyNbxW1−xO3−x/2) fall between 0.2 and 0.3, and the phase transition was found to depend on the conditions of the reaction. Changes in OCV and lattice parameters in tetragonal region (y<0.2) were discussed from the viewpoint of the ordering of lithium ions. Also, the component diffusion coefficient of lithium in tetragonal compounds Li0.1NbxW1−xO3−x/2 (0≤x≤0.23) was found to increase with niobium content when x≤0.10, and to saturate at 4×10−9 cm2/s.