Characterization of the Electronic Conduction Parameter of Cation Conducting Solid Electrolytes

The thesis aims at the characterization of the p-electronic conduction parameter of cation conducting solid electrolytes. For this purpose potentiometric as well as thermoelectric measurements were carried out. The investigations have been done on commercially available potassium and sodium beta alumina as well as on laboratoryprepared samples of NASICON. The information about the p-electronic conduction parameter of K-beta-Al2O3 was obtained by evaluating the voltage of various galvanic cells using two different reference electrodes under variable measuring conditions, i.e. temperature (593 to 893 K) and potassium chemical potential of the electrodes. Under isothermal condition, a non-linear chemical potential dependence of the voltage response of galvanic cell is obtained. From the results obtained it is evident that the p-electronic conduction parameter of the solid electrolyte is not a constant but adapts to the potassium chemical potential in the surroundings which confirms previous findings on sodium beta alumina. Using the same technique the electronic conduction parameter of NASICON was characterized as a function of the sodium chemical potential at the measuring electrode as well as of the temperature. To prove the consistency of electronic conduction properties obtained from potentiometric methods on sodium beta alumina, another independent technique without employing a secondary electrode i.e. thermoelectric power measurement, was performed. The p-electronic conduction parameters obtained from thermoelectric power and potentiometric methods are in excellent agreement with each other. In addition, the impact of the electronic conduction on the behaviour of potentiometric cells was evident by evaluating thermodynamic data on the system pyrochloreNaSbO3. As a consequence, the thermodynamic stability obtained from these measurements proves to be much higher compared to that reported in the literature, thereby again confirming the non-conventional properties of the electronic conductivity of beta alumina.