Thermodynamic Stability and Electronic Conductivity of Na-beta-Alumina

Until now the thermodynamic stability of Na-beta (a + 3/p3 + 3"/p3)-alurnina has been determined exclusively by meas-uring the potential on appropriate solid electrolyte galvanic cells and evaluating the results according to the Nernst equa-tion. In this paper the validity of Nernst's law for these measurements is critically discussed in the light of the electronic conductivity data published so far for Na-beta-alumina. The following conclusions have been drawn: (i) the stability meas-urements may be adversely affected by electronic conduction when the sample is exposed to a comparatively high oxygen pressure, e.g., air, and (ii) the recently reported findings on the p-electron conduction parameter, which contradicted the literature data, describe the electronic properties of Na-beta-alumina more accurately than the previous results. Infrocluction Due to the relevance of Na-beta-alumina as a sodium ion conducting solid electrolyte, it is important to know its thermodynamic stability. To date, this property has been exclusively determined by means of electrochemical meas-urements on galvanic cells.''4 Except in one case,' ° the underlying principle has always been the same. This prin