Solid-oixide electrolytes offer the prospect of conducting electrochemistry at high temperatures and in reactive environments; one present application is for monitoring oxygen levels in combustion exhaust streams. Existing systems use porous metallic films deposited on solid electrolytes; while functional, such systems have low effeciency, apparently because only the three-phase (metal, electrolyte, gas) boundary is active. This study seeks to overcome this problem by use of metal oxides that exhibit conductivity for both electrons and oxygen ions. Specifically, the kinetics of oxygen exchange between the gas phase and a family of electrolytes with the perovskite structure, lanthanum-doped calcium manganate (LaxCa1-xMn03), is investigated. Electronic and ionic properties can be varied by changing the doping level. Techniques for preparing these materials in useful forms will be perfected. Electrochemical kinetics are measured using steady-state and transient electrochemical techniques; conductivities are measured using AC impedance methods; and surface chemistry is probed using temperature-programmed desorption and Auger election spectroscopy. This study could have very wide impact. The most immediate impact will be in systems using oxygen sensors including control systems for automotive carburetion and exhaust control, and for incineration. This work should reduce the size, extend the useful temperature range, and improve the sensitivity of these sensors. Similar electrodes should be useful in fuel cells, electrolyzers, and other electrochemical devices. The work is also applicable to other high-performance ceramics, notably the closely related "defect perovskite superconductors."
