Oxide ion conductivity in Bi2W1−xMExO6−x/2 (ME = Nb, Ta)
Oxygen deficient Bi2WO6 phases have been synthesized by substitution for WVI with NbV and TaV, in this m = 1 member of the Aurivillius series. The composition range of the solid solutions is limited to 0 < x < 0.15 according to a formula Bi2W1−x(Nb or Ta)xO6−x/2. The maximum oxygen ion conductivities are obtained when x = 0.05 for both phases with moderate activation energies. The performances are intermediate between those of the high conductor BIMEVOX phases and those of doped higher members of the Aurivillius series m = 2, 3 and 4. These results provide the first experimental evidence of the predominant role of the Bi3+ 6s2 lone pair in the oxide ion diffusion process within these layered phases.