Electrochemical Determination of the Activity of Na2O in the Pyrochlore Phase of the Sb₂O₄‐NaSbO₃ System

Abstract

The solid electrolyte used in the above electrochemical cells is Na-␤-Al 2 O 3 , which is an excellent sodium-ion conductor in the temperature range of the measurements. From the measured reversible emf, the activity of Na 2 O in the Sb 2 O 4 -NaSbO 3 system has been calculated. The temperature dependence of the logarithm of the activity of Na 2 O in various two-phase regions of the Sb 2 O 4 -NaSbO 3 system can be represented as log a Na 2 O (␣-Sb 2 O 4 + pyrochlore (24 mol% Na 2 O)) = −1.1342 − 10256 T (±0.3) log a Na 2 O (pyrochlore (35 mol% Na 2 O)) = −4.7171 − 4718 T (±0.3) log a Na 2 O (pyrochlore (37.5 mol% Na 2 O)) + NaSbO 3 ) = −5.3108 − 3503 T (±0.3)No thermodynamic data have been reported earlier in the literature for the system Sb 2 O 4 -NaSbO 3 , and the present data constitute the first thermodynamic information.

Determining Extremely Low Sodium Activities at Elevated Temperatures

“…The electrochemical characterization of the thermodynamic stability of heterogeneous phase equilibria comprising sodiumcontaining compounds, such as Na-␤-Al 2 O 3 /Na-␤Љ-Al 2 O 3 , 1 Na 2 ZrO 3 /ZrO 2 , 2 or NaSbO 3 /Sb 2 O 4 , 3 usually comes down to the determination of the sodium activity of these phase mixtures. This is accomplished by means of potentiometric measurements on galvanic cells using a sodium ion conductor, e.g., Na-beta-Al 2 O 3 or NASICON, as solid electrolyte.…”