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

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=...

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Bibliographic Details
Authors: Díaz Guillén, M. R., Moreno, K. J., Díaz Guillén, J. A., Fuentes, A .F., Naval, K. L. Ngai, Garcia Barriocanal, Javier, Santamaría Sánchez-Barriga, Jacobo, León Yebra, Carlos
Format: article
Publication Date:2008
Country:España
Institution:Universidad Complutense de Madrid (UCM)
Repository:Docta Complutense
Language:English
OAI Identifier:oai:docta.ucm.es:20.500.14352/51401
Online Access:https://hdl.handle.net/20.500.14352/51401
Access Level:Open access
Keyword:537
Electrical relaxation
Constituent oxides
Coupling model
Spin ice
Conductivity
Migration
Diffusion
Gd_(2)Ti_(2)O_(7)
Glasses
Melts.
Electricidad
Electrónica (Física)
2202.03 Electricidad
Description
Summary: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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