Intrinsic Structures and Electrochemical Properties of Floating Zone Grown Nb₁₂WO₃₃ and Nb₁₄W₃O₄₄ Single Crystals

“Wadsley–Roth”-phased crystal structures have defied accurate crystallographic determination since their discovery in 1965. These structurally challenging materials comprise transition-metal oxides whose condensate oxygen vacancies give rise to intricate structures and short-range order compounded by second-order Jahn–Teller distortions experienced by the d0 cations. Structural studies have been hampered by the small crystals obtained from annealing, which led to unclear resolutions on the precise space groups of the materials. Herein, we present our study on high-quality crystals of centimeter size obtained by using the laser diode floating zone technique and a traveling solvent method. We find additional symmetry than previously assumed. Nb12WO33 crystallizes in I2/m and Nb14W3O44 in the I4/m space group. We also find oxygen-deficient (reduced) crystals to have significant twinning and drastically different electrochemical properties when cycled against a lithium anode from their oxidized counterpart.