(Invited) Oxide Ion Conductivity and Oxide Vacancy Diffusion Coefficient of Stabilized ZrO2 and Doped CeO2 Discussed Based on Classical Defect Chemistry with Particular Focus on Valence State (2+, 3+, and 4+) of Doped Cations
Authors: Mizusaki Junichiro 
Published: February 2024

So far tremendous works have been reported on the oxide-ion conductivity of fluorite-type oxides typically stabilized zirconia and doped ceria. It is well known that the oxide-ion conductivity vs. dopant concentration plot shows maximum around 10 mol percent dopant concentration and the maximum conductivity varies with the dopant species. Interests tend to be focused on the higher and the stabler conductivity. For the aim, explorations are made on the dopant survey and the phase stability of the solid solution.

Generally, conductivity is considered proportional to the product of carrier concentration and carrier mobility. For the fluorite-type oxide ion conductors, it is considered that carrier is oxygen vacancy, V
O
··, and mobility is proportional to oxygen vacancy diffusion coefficient, DV
. However, such defect chemical approach to the fluorite-type oxides is not popular. When we assume that the mobility is constant following the classical hypothesis, we cannot explain the conductivity maximum.

The author has been trying to discuss the oxide-ion conduction in fluorite-type oxide solid solutions in terms of oxygen vacancy concentration, cV

,and DV
.

Using the literature data on conductivity and composition relationship, the author has already calculated DV
for some compositions of stabilized zirconia and doped ceria as a function of composition. The data have been published in a short review [1] and books [2,3]. However, the published graphical displays were so crowded that the physical meanings seem still unclear.

In this presentation, discussion is made on the conductivity of stabilized zirconia and doped ceria in the following order to make clear the characteristic feature of DV
with the variation of valence state and chemical species of dopant oxides.

1: zirconia base solid solutions

1a: with divalent cation oxides

1b: with trivalent cation oxides

2: ceria base solid solutions

2a: with divalent cation oxides

2b: with trivalent cation oxides

3: stabilized zirconia – ceria solid solutions

3a: stabilized zirconia base solid compositions

3b: ceria base solid compositions

3c: trivalent cerium formation by partial reduction

It is clarified that DV
of fluorite type oxide is affected by the dopant cation not only by different valent but also by the same valent cations.

References:

[1] Junichiro Mizusaki, Tatsuya Kawada, Yutaka Nigara and Kenichi Kawamura, ISSI Letters, 9(1), 2-6(1999).

[2] Junichiro Mizusaki, Keiji Yashiro, Nano-Mega Scale Flow Dynamics in Energy Systems, The 21st Century COE Program, International COE of Flow Dynamics, Lecture Series, Vol. 9. Ed Shigenao Maruyama, Tohoku Univ. Press (total 240 pages), 9, 39-78(2008).

[3] Junichiro Mizusaki, in New Research Trends of Fluorite-Based Oxide Materials, From Basic Chemistry and Materials Science of Engineering Applications, Ed by A. Nakamura and J. Mizusaki, Materials Science and Technologies, Nova Science Publishers, Inc. New York, ISBN 978-1-63117-350-9(hard cover), 978-1-63117-351-6 (e-book), Chapter 1, 1-28(2015).