Oxide Ion and Hole Conduction in Grain and Grain Boundary of Defect Perovskite-Type SrZr_1-xAl_x0_3-α

Abstract

The electrical conductivity of defect perovskite-type oxides, SrZr_1-xAl_x0_3-α (0.02≤x≤0.15), has been investigated to clarify the effect of aluminium doping both on the oxide ion conduction and on the hole conduction in the grain as well as in the grain boundary of the oxides. The complex impedance of these oxides was measured as a function of temperature and oxygen partial pressure. The possible equivalent circuit for a mixed condu ctor was considered to be expressed by a series of the grain impedance and the grain boundary impedance, Jpoth of which are composed of a parallel combination of resistance and capacitance based on the oxide cie ion conduction and resistance based on the hole conduction (Fig.1). The resistance and capacitance of the grain and the grain boundary based on the oxide ion conduction were independent of P_o2. On the other hand, both the resistance of the grain and the grain boundary based on the hole conduction varied significantly with P_o2, showing the hole conductivity in both of them to be proportional to P_o21/4 (Fig.7). It is revealed that the discussion of an electrical conductivity of a mixed conductor can be carried out in more detail, than ever by employing the complex impedance analysis based on the equivalent circuit proposed in this study. The solubility limit of Al₂0₃in SrZr0₃ was deduced to be close to 2mol % from the variation in the unit cell volume, the activation energy for migration of oxide ion vacancy, and the oxide ion transference number, the last two properties being resolved for the grain and the grain boundary, respectively, by the analysis of the complex impedance plots for the oxides (Figs.9, 11). Furthermore, both oxide ion conductivity and oxide ion transference number of the SrZr_1-xAl_x0_3-α system were concluded to be controlled by the behavior of oxide ion in the grain boundary.