Electronic and silver ionic conductions in perovskite and related oxides

Abstract

Electronic and silver ionic conductivities in some silver-containing oxides with perovskite and related structures, such as AgNbO 3 (perovskite), AgSbO 3 (pyrochlore-related structure), and Ag-doped Bi (Pb) Sr Ca Cu O-system superconductor, were measured by four-probe techniques using Pt electrodes and Ag-β″-Al 2O 3 electrodes with silver ionic conduction, respectively. Both AgNbO 3 and AgSbO 3 were n-type semiconductors and their electronic conductivities increased with an increase in the silver content. The electronic conductivity of AgSbO 3 was higher than that of AgNbO 3, due to the presence of a large amount of oxygen vacancies. Sb 4+ and/or Sb 3+ in AgSbO 3, and Nb 4+ in AgNbO 3 will act as a donor. Silver ionic conductivities were always lower than the electronic conductivities brought about by the above donors for both AgNbO 3 and AgSbO 3 ceramics. The activation energies of silver ionic conductivity were in the ranges of 1.01–1.58, 0.78–0.90, and 0.94–1.12 eV for AgNbO 3, AgSbO 3, and Ag-doped Bi-system superconductors, respectively. The silver ion was assumed to move via the Ag sites in the bulk for AgNbO 3, but to move in the grain boundaries for AgSbO 3 and the Bisystem superconductor. The mechanisms of the electronic and silver ionic conductions are discussed for the present oxide ceramics.