Electronic and silver ionic conductions in perovskite and related oxides

Electronic and silver ionic conductivities in some silver-containing oxides with perovskite and related structures, such as AgNbO3 (perovskite), AgSbO3 (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 double-prime-Al2O3 electrodes with silver ionic conduction, respectively. Both AgNbO3 and AgSbO3 were n-type semiconductors and their electronic conductivities increased with an increase in the silver content. The electronic conductivity of AgSbO3 was higher than that of AgNbO3, due to the presence of a large amount of oxygen vacancies. Sb4+ and/or Sb3+ in AgSbO3, and Nb4+ in AgNbO3 will act as a donor. Silver ionic conductivities were always lower than the electronic conductivities brought about by the above donors for both AgNbO3 and AgSbO3 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 AgNbO3, AgSbO3, and Ag-doped Bi-system superconductors, respectively. The silver ion was assumed to move via the Ag sites in the bulk for AgNbO3, but to move in the grain boundaries for AgSbO3 and the Bi-system superconductor. The mechanisms of the electronic and silver ionic conductions are discussed for the present oxide ceramics