ELECTRODES FOR OXYGEN SENSORS BASED ON RARE-EARTH MANGANITES OR COBALTITES

Rare earth manganites and cobaltites are particularly suitable electrode materials for solid electrolyte oxygen sensors. Perovskite-type manganites Ln1-xCa(Sr)xMnO3 (Ln = La, Nd, Gd, Yb, Y; x = 0-0.5) and cobaltites Ln1-xSrxCoO3 (Ln = La, Pr, Nd, Sm; x = 0-1), SrCo1-xFexO3 (x = 0-0.5) were prepared in air by sintering at T = 1270-1570 K. The formation of the perovskite-type phase was confirmed by X-ray powder diffraction results. The cation concentrations were determined by atom absorption spectroscopy. Isothermal oxygen permeation measurements were performed with zirconia solid electrolyte tubes by using a special glass for sealing and adjusting the oxygen solid electrolyte pump. From ultraviolet photoemission spectroscopy (UPS) we determined the work function PHI of electrons, the position of the Fermi level in relation to the valence band edge (E(F)-E(V)), and the change of the ionization potential (DELTAI) as a function of temperature. The polarization resistivity of perovskite-type oxide electrodes on Bi0.75Y0.25O1.5 solid electrolytes was determined from the steady-state current density overpotential curves which were measured in a three-electrode arrangement.