Figure 1. Crystal structures and particle morphology of Li_1.3Nb_0.3Me_0.4O₂.

Synchrotron X-ray diffraction (SXRD) patterns of as-prepared 0.43 Li₃NbO₄–0.57 LiMeO₂ (Me=Fe³⁺, Mn³⁺, and V³⁺) samples, which are reformulated as Li_1.3Nb_0.3Me_0.4O₂ based on the formulation of α-NaFeO₂-type layered structure, are shown. SXRD patterns of the samples, Me=Fe³⁺ and Mn³⁺, were also shown in our previous work²⁰. The samples crystallize into the cation disordered rocksalt structure with lattice parameters of 4.19 Å for Fe³⁺, 4.21 Å for Mn³⁺ and 4.17 Å for V³⁺. Structural analysis was carried out using RIETAN-FP (ref. ⁴¹). Substitution of Fe³⁺, Mn³⁺ and V³⁺ for Nb⁵⁺/Li⁺ results in the donation of d electrons in a conduction band, and thus colour of the samples changes from white for Li₃NbO₄. Data of Li₃NbO₄ (Li_1.5Nb_0.5O₂) are also shown for comparison. Schematic illustrations of the crystal structures were drawn using the program VESTA (ref. ⁴²).