Oxide-ion conduction and dielectric relaxations in Ca-stabilized ZrO₂

Abstract

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...

Terahertz probing of low‐temperature degradation in zirconia bioceramics

“…It is anticipated that the distance in the Non‐LTD 1700 ceramics will be greater than that in the Non‐LTD 1500 sample, which is related to the fact that the higher sintering temperature allows for larger translational movements of oxygen vacancies. Oxygen associates with the different distance between and have been reported in Ca‐doped ZrO 2 ceramics 43 . Therefore, the higher dielectric permittivity and loss of the Non‐LTD 1700 ceramics can be attributed to a possible long distance between and in the oxygen vacancy associated () dipoles.…”

“…For Y (8 and 9 mol%) doped ZrO 2 , it was reported that these defect dipole pairs are responsible for the dielectric relaxation at radio frequencies. 22,43 There is 2.1% and 7.7% of the monoclinic M phase in the Non-LTD 1500 and Non-LTD 1700 samples. The lower percentage of the M phase, the higher concentration of the oxygen vacancy related associates.…”

“…The frequency dependence of the dielectric permittivity, characterized by the decreasing permittivity with the increasing frequency, can be attributed to the contributions of oxygen vacancy associated () dipoles. For Y (8 and 9 mol%) doped ZrO 2 , it was reported that these defect dipole pairs are responsible for the dielectric relaxation at radio frequencies 22,43 . There is 2.1% and 7.7% of the monoclinic M phase in the Non‐LTD 1500 and Non‐LTD 1700 samples.…”

“…Oxygen associates with the different distance between 𝐶𝑎 ′′ 𝑍𝑟 and 𝑉 .. 𝑂 have been reported in Ca-doped ZrO 2 ceramics. 43 Therefore, the higher dielectric permittivity and loss of the Non-LTD 1700 ceramics can be attributed to a possible long distance between 𝑌 ′ 𝑍𝑟 and 𝑉 .. 𝑂 in the oxygen vacancy associated (𝑌 ′ 𝑍𝑟 − 𝑉 .. 𝑂 ) dipoles. Zhang et al 20 have shown that a longer dipole (e.g., a longer distance between 𝑌 ′ 𝑍𝑟 and 𝑉 .. 𝑂 in our samples) may produce a higher permittivity under the same AC electric field.…”

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

“…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) in the Sm, Nd, or Yb doped CeO 2 [4][5][6] and Y or Ca stabilized ZrO 2 [7,8] systems. According to those studies, the dielectric properties of oxide ion conductors can be explained by the superposition of Debye-type polarization due to the dopant-vacancy associates [Ln Ce ′-V O¨] ‧ (Ln: dopant cation) and charge current on electrolyte-electrode interface.…”