The effect of annealing on the concentration of Wadsley defects in the Nb 2O 5WO 3 system

Mixtures of xNb ₂O ₅ · yWO ₃ with x: y = 9:8, 8:5, and 8:1 have been annealed at high temperatures for prolonged periods before quenching to room temperature. The concentration of Wadsley defects, estimated from lattice image electron micrographs of a few fragments in each sample, is reduced during this treatment. The results indicate that (1) the high temperature equilibrium is attained very slowly, and in stoichiometric samples probably involves the complete removal of Wadsley defects; (2) the high temperature situation is not seriously affected by the quenching treatment; and (3) variations in stoichiometry may be accommodated by means other than the presence of Wadsley defects.