A radiation-induced order-disorder transformation occurs in many A[2]B[2]O[7] pyrochlore structure-types by disordering of the A- and B-site cations, as well as anion vacancies. The ionic conductivity increases up to two orders of magnitude due to this order-disorder transformation. This irradiation-induced order-disorder transition has been examined in detail using ion beam irradiations and in situ transmission electron microscopy. Under ion irradiation, the ordered pyrochlore superstructure transforms to an anion-disordered pyrochlore prior to a final transformation to a cation-disordered defect-fluorite structure-type. The anion-disordered pyrochlore structure displays a partial ordering of the A- and B-site cations and complete disordering on the anion array-as evidenced by the disappearance of characteristic diffraction maxima resulting from ordering of the oxygen sublattice. These results suggest that anion disorder precedes cation disordering in the pyrochlore structure.

Citation: Lian J., Wang L., Chen J., Sun K., Ewing R.C., Farmer J.M., Boatner L.A. "The Order-Disorder Transition in Ion-Irradiated Pyrochlore." Acta Materialia. 51(5) 14 March 2003:1493-1502(10).

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