Oxide ion conduction and dielectric relaxations for Ce_1-<i>x</i>Y_<i>x</i>O_2-<i>x</i>/2 system.

Abstract

Relationship between oxide ion conduction and dielectric relaxation in the Ce 1-x Y x O 2-x/2 system (0 x 0.5) was investigated in order to clarify the dynamic properties of oxide ion conduction. The frequency dependence of dielectric constant was explained by the superposition of Debye-type polarization due to dopant-vacancy associates and charge current on electrolyteelectrode interface. The frequency dependence of ac conductivity was also explained by use of the dielectric parameters obtained from the numerical analysis of dielectric constant. Additionally, the polarization hysteresis curves of the oxide ion conductor were also measured to investigate the Debye-type dipoles in detail. As a result, it was found that the observed remanent polarizations have a close relation with the polarization of dopant-vacancy associates.Key words: CeO 2 , dielectric relaxation, fluorite type structure, oxide ion conduction IntroductionOxide ion conductors play an important role in such applications as oxygen sensors, oxygen pumps and solid oxide fuel cells (SOFCs) etc. Since SOFCs are required to decrease the operation temperature, high ionic conductivity is desired. Therefore, various materials having fluorite, perovskite and their related structures have been investigated. So far, the oxide ion conduction has been investigated by the dc four-probe and/or the ac impedance methods, and then the relationship between the crystal structure and activation energy for oxide ion conduction was discussed. As the result, many researchers suggest many factors for oxide ion conduction, for example, unit cell free volume, saddle point, ordering of oxygen vacancy and dopant-vacancy association etc. [1][2][3] However, the dominant factors for oxide ion conduction have not been clear.The oxide ion conduction has a close relation with the electric dipole polarizations of oxygen vacancy. Our research group reported that the relationship between oxide ion conduction and dielectric relaxation from the viewpoints of dielectric constant, dielectric loss factor and loss tangent (tanδ)