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

A critical view is presented of the feasibility and reliability of electrochemical sensors combining Na-β-alumina (i.e. Na2O·xAl2O3) solid electrolyte material with an in-situ created auxiliary phase and electrochemical sensors using a Na-β-alumina based reference. Thermodynamic information on the stability of Na-β-alumina and the activity of Na2O in the Na2O–xAl2O3 binary system and in the Na-β-alumina phase in particular, is critical in applications for sensors, and especially in situations where the operating temperatures are high and the oxygen pressures are low and where the Na-β-alumina phase is used as a part of the electrode providing reference potentials in galvanic cells.