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The Λ-sensor is used within the scope of the Bosch emission control system, representing a closed control loop. In principle, it is an oxygen concentration cell with an oxygen ion-conducting solid electrolyte which provides a sharp voltage step at the stoichiometric air-fuel ratio, serving as a control signal. Zirconia ceramic stabilized with certain metal oxides is used as the solid electrolyte. The electrical and mechanical properties of the ceramic depend, above all, on the type and concentration of the stabilizing oxide and on the manufacturing conditions. Using ceramic materials which are described, sensors can be produced that make possible exact control of the stoichiometric A/F in a temperature range of 300/400-900°C. The lifetime of the sensor, which depends on the operating conditions, can be taken as about 15,000 miles of driving distance. With this sensor, exhaust emissions can be kept below the limits specified for 1977-1978 in the United States.