Cation size effects in oxygen ion dynamics of highly disordered pyrochlore-type ionic conductors

M. R. Díaz-Guillén, K. J. Moreno, J. A. Díaz-Guillén, A. F. Fuentes, K. L. Ngai, J. Garcia-Barriocanal, J. Santamaria, C. Leon

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Abstract

In this work we evaluate the effect of cation size on the dc activation energy needed for oxygen ion migration, Edc, in highly disordered pyrochlore-type ionic conductors A2 B2 O7. Twenty six compositions with the general formula, Ln2 Zr2-y Tiy O7, Ln1.7 Mg0.3 Zr2 O7 (Ln=Y, Dy, and Gd), and Gd2-y Lay Zr2 O7, were prepared by mechanical milling, and their electrical properties were measured by using impedance spectroscopy as a function of frequency and temperature. By using the coupling model we also examine the effect of cation radii RA and RB on the microscopic potential-energy barrier, Ea, which oxygen ions encounter when hopping into neighboring vacant sites. We find that, for a fixed B -site-cation radius RB, both activation energies decrease with increasing A -site-cation size, RA, as a consequence of the increase in the unit-cell volume. In contrast, for a given RA size, the Edc of the Ln2 Zr2-y Tiy O7 series increases when the average RB size increases. This behavior is associated with enhanced interactions among mobile oxygen ions as the structural disorder increases with RB.

Original languageEnglish (US)
Article number104304
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume78
Issue number10
DOIs
StatePublished - Sep 19 2008

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