INFLUENCE OF CONSTITUENT METAL-CATIONS IN SUBSTITUTED LACOO3 ON MIXED CONDUCTIVITY AND OXYGEN PERMEABILITY

Oxide-ion and electronic conductivities of perovskite-type oxides, La0.6A'0.4Co0.8Fe0.2O3-delta (A' = La, Ca, Sr) and La0.6Sr0.4Co0.8B'0.2O3-delta (B' = Fe, Co, Ni, Cu), were separately measured at 770-1150 K in air by means of a four-probe ionic dc technique (electron-blocking method) and a standard four-probe dc technique, respectively. In addition to high electronic conductivities ranging from 10(2) to 10(3)S cm-1, the present oxides showed high ionic conductivities comparable or superior to those of yttria-stabilized zirconia, being proven to be excellent mixed conductors. The ionic conductivities could increase greatly with the substitution of lower valence cations for A and B sites, in accordance with an increase of oxide ion vacancies, although they could also differ considerably even for constituent metals with the same valency. The oxygen permeability of these mixed conductors was found to increase with an increase in ionic conductivity.