Determination of the p-Electron Conduction Parameter of Na-beta-Alumina by Potentiometric Measurements

The p-electron conduction parameter a ⊗ of Na-beta-Al 2 O 3 is determined by quantitatively evaluating the isothermal voltage response of the cell Au|O 2 , CO 2 , Na 2 CO 3 |Na-beta-Al 2 O 3 |NiO, FeO (glass)|FeNi48|Au to successive variations of the sodium activity of the measuring electrode. Within the temperature interval under investigation (320 ≤ T ≤ 620) the results on a ⊗ lie at the upper limit of the scatter range spanned by previous results on this parameter. In a log a ○+ vs. 1/T diagram the data points describe sections of straight lines with two different slopes that are identical with the temperature dependence of either the measuring or the reference electrode potential, respectively, depending on which of these electrodes has the comparatively lower sodium activity. These findings confirm the fact previously observed that a ⊗ is not a constant but adapts to the sodium activity in the surroundings of the electrolyte. It can be understood as a consequence of a variable stoichiometry in the composition of the electrolyte and enables a conclusive account for the apparent differences in the literature with respect to the impact of the electronic conductivity on the behavior of a potentiometric solid-state gas sensor with Na-beta-alumina as electrolyte.

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