Important materials aspects for sensors based on Na-beta-alumina

A critical view is presented of the feasibility and reliability of electroc hemical sensors combining Na-beta -alumina (i.e. Na2O . xAl(2)O(3)) solid e lectrolyte material with an in-situ created auxiliary phase and electrochem ical sensors using a Na-beta -alumina based reference. Thermodynamic inform ation on the stability of Na-beta -alumina and the activity of Na2O in the Na2O-xAl(2)O(3) binary system and in the Na-beta -alumina phase in particul ar, is critical in applications for sensors, and especially in situations w here the operating temperatures are high and the oxygen pressures are low a nd where the Na-beta -alumina phase is used as a part of the electrode prov iding reference potentials in galvanic cells. (C) 2000 Elsevier Science B.V . All rights reserved.