Frequency dependences of dielectric constant e r ö for 9 mol! Y 2 O 3 doped ZrO 2 YSZ single crystal which is a typical oxide-ion conductor was successfully explained by the superimposition of both electrolyte-electrode interfacial and Debye-type polarizations. Three kinds of Debye-type polarizations were observed at fairly high temperatures. The two polarizations were ascribed to defect associates,, which were observed in the tan d spectra. The third polarization in the high frequency region was ascribed to a long range migration of oxygen vacancy, which was observed in the M ÷spectra. The s ac dispersion was also explained by the Debye-type polarizations.

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The dielectric properties of Ca-stabilized ZrO 2 (Zr 0.9 Ca 0.1 O 2-δ , 10CSZ) which is an oxide ion conductor were investigated. Numerical analyses for the frequency dependence of dielectric constant (ε r ′) and dielectric loss factors (ε r ″) revealed that the dielectric properties were made up of Debye-type polarization due to dopant-vacancy associates [Ca zr ″-V o¨] and interfacial polarization at electrolyte-electrode. Two Debye-type relaxations were observed. This result implies the existence of two dopant-vacancy associates with different distances. Moreover, by using the dielectric constants obtained from the numerical analysis, the frequency dependences of ac conductivity (σ ac ) and dielectric loss tangent (tanδ) were also explained. KEYWORDS: oxide-ion conductor, fluorite-type structure, dielectric relaxation, Debye-type polarization, dopant-vacancy associate IntroductionThe oxide-ion conductors are used in various applications, such as oxygen sensors, oxygen pumps, solid oxide fuel cells (SOFCs), etc. However, since their operation temperatures are very high, the decrease in the operating temperature is required to achieve efficient operation and high performance. For oxide-ion conduction, many researchers have extensively investigated the electrical properties for fluorite-based oxides, ZrO 2 and CeO 2, and perovskite-based oxides, LaGaO 3, and Ba 2 In 2 O 5 [1-4]. Oxide-ion conductivity was estimated by using both ac impedance method and/or dc four-probe method and the relationships between activation energy and crystal chemical factors have been discussed. It has been clarified that the material with high conductivity has a highly symmetrical structure, relatively large unit cell free volume, disordered oxygen vacancies and other crystal properties that may be the dominant parameters of oxide-ion conductivity.On the other hand, experimental dates concerning the conduction mechanism are limited. Then, we paid attention to the dielectric properties of oxide-ion conductor, in order to reveal the polarization mechanism of the oxide-ions and the vacancy-dopant pairs. Recently, the group of present authors have clarified that the frequency dependence of dielectric constant (ε r ′) and dielectric loss factors (ε r ″) in the Ca, Nd, Sm, or Yb-doped CeO 2 systems, which are typical oxide ion conductor [5][6][7][8]. It was revealed that the dielectric properties can be made up of Debye-type polarization due to dopant-vacancy associates [Ca zr ″-V o¨] and interfacial polarization of electrolyte-electrode. In addition, when the dielectric measurement was carried out for the sample with oxide electrode La 0.6 Ca 0.4 MnO 3 (LCM), the observed dielectric properties are remarkably different from those of platinum electrode [9]. For this phenomenon, it was speculated that in the case of oxide electrode, oxide-ion of electrode can occupy directly the oxygen-vacancy site of the electrolyte, resulting in the decrease in the dopant-vacancy associate.In the present study, we tried to apply the numerical analysis of c...