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clea orm ine z t urso)] i lk c ssu ollo or d # 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Nernst oxygen sensors based on partially stabilized zirconia solid electrolytes, which are oxide ion conductors, are not potentiometric mode due to their logarithm dependence on the Available online at www.sciencedirect.com Ceramics International 35 (2oxygen in the exhaust gas of combustion engine vehicles to control the air–fuel ratio at levels close to stoichiometry to minimize emission of pollutants and (2) in harsh chemical environment at high temperatures during processing of molten steel. In steelmaking processes, control of oxygen levels in the molten steel is essential and this control is usually done with electrochemical oxygen probes. These probes consist of a solid electrolyte and a reference electrode and several components like thermocouple, refractory case, and metallic terminal leads for measuring the electromotive forces resulting from the solid oxygen level [3]. The measurement of oxygen in molten metals has already been achieved using a variety of beta aluminas [4,5] based on the fact that it is not required that the element to be sensed is the mobile ion in the electrolyte. Ion exchange at the surface of the electrolyte can occur and the element can be sensed [5]. Nernstian oxygen sensors based on a strontium, calcium or lanthanum ion conducting electrolyte with a beta-alumina type structure have been developed [5,6]. These sensors respond to lower oxygen contents than the conventional oxygen sensors based on stabilized zirconia. In this paper the electrical behavior of LaAl11O18 (La–b-Al2O3) solid electrolytes is described. Emphasis is done on the evaluation of the emf response of nearly single phas