Abstract: | The ionic conductivity of pyrochlores A1+α(Ta1+αW1?α)O6 was investigated for A = Na and T1. The thallium compounds are rather good conductors (0.34 ≤ ΔE ≤ 0.40 eV and ); the sodium oxides are poor conductors (0.76 eV ≤ ΔE ≤ 1.48 eV and ). The differences between these two classes of pyrochlores are explained in terms of structure. New non-stoechiometric oxides T112+x(M30+xW3?x)O90, with M = Ta, Nb, and 0 ≤ x ≤ 3, were isolated. They are, like pyrochlores, characterized by an intersecting tunnel structure, which is an intergrowth of pyrochlore and A2M7O18 structures. These oxides show ionic conduction properties which are very close to those of pyrochlores: the tantalum oxides are better conductors (0.30 eV ≤ ΔE ≤ 0.37 eV ; ) than the niobium oxides (0.36 eV ≤ ΔE ≤ 0.42 eV ; ). The evolution ofionic conduction properties of all these compounds is discussed. |