Oxide Ion Conduction via Interstitial Sites in the Substituted Scheelite- and Spinel-type Oxides

Abstract

In the purely academic interests to find new and high oxide ion conductors, we investigated on the electrical conduction in the substituted scheelite- and spinel-type oxides. In the former, the substitution methods shown by Pb_1−xLn_xWO_4+x/2 and Pb_1−xLn_2x/3WO₄ (Ln: Lanthanoid element) to intend to increase the concentration of defects brought about formation of the PbWO₄-based scheelite-type solid solutions, where the enhanced oxide ion conductivities were observed compared with that of the based material. From the structural and density measurements, the charge carriers in those phases were considered to be interstitial oxide ions. On the other hand, electrical conduction was also studied in many substituted spinel type oxides. Although the oxide ions would be generally hard to move considering from their cubic-packed form, the enhanced oxide ion conductivities were observed in the inverse spinel type solid solutions based on Zn₂TiO₄. A typical sample was Zn_2−x/2Ti_1−xTa_xO₄, the ionic conduction of which was considered to be due to the interstitialcy oxide ion migration. These results are mentioned in relation to the defect crystal phases.