%0 Journal Article
%A Díaz Guillén, M. R.
%A Moreno, K. J.
%A Díaz Guillén, J. A.
%A Fuentes, A .F.
%A Naval, K. L. Ngai
%A Garcia Barriocanal, Javier
%A Santamaría Sánchez-Barriga, Jacobo
%A León Yebra, Carlos
%T Cation size effects in oxygen ion dynamics of highly disordered pyrochlore-type ionic conductors
%D 2008
%@ 1098-0121
%U https://hdl.handle.net/20.500.14352/51401
%X In this work we evaluate the effect of cation size on the dc activation energy needed for oxygen ion migration, E_(dc), in highly disordered pyrochlore-type ionic conductors A_(2)B_(2)O_(7). Twenty six compositions with the general formula, Ln_(2)Zr_(2−y)Ti_(y)O_(7), Ln_(1.7)Mg_(0.3)Zr_(2)O_(7) (Ln=Y, Dy, and Gd), and Gd_(2−y)La_(y)Zr_(2)O_(7), 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 R_(A) and R_(B) on the microscopic potential-energy barrier, E_(a), which oxygen ions encounter when hopping into neighboring vacant sites. We find that, for a fixed B-site-cation radius R_(B), both activation energies decrease with increasing A-site-cation size, R_(A), as a consequence of the increase in the unit-cell volume. In contrast, for a given R_(A) size, the E_(dc) of the Ln_(2)Zr_(2−y)Ti_(y)O_(7) series increases when the average R_(B) size increases. This behavior is associated with enhanced interactions among mobile oxygen ions as the structural disorder increases with R_(B).
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