Abstract: A sensor for measuring partial pressures of oxygen with an ion-conducting lid electrolyte of zirconium dioxide as the sensor element, which is arranged between two electrodes for measuring an electrically measurable quantity, is improved so that it is usable at an operating temperature of about 200.degree. C., by providing that the zirconium dioxide as the solid electrolyte is solely in its tetragonal modification and containing an addition of about 2-3 mol % yttrium oxide.

Abstract: A solid state cell for measuring the activity of a component of a mixture using a solid ionic conductor, which is in contact on one side with a reference phase and on the other side with a phase sensitive to the gas component to be determined, is to be improved in such a manner that its detection sensitivity and measuring stability are increased. For this purpose, the gas sensitive phase contains an addition of a substance that increases the electronic conductivity and does not chemically react with the components of the sensitive phase and the gas to be determined.