IRREVERSIBLE CONDUCTIVITY CHANGE OF CA BETA''-ALUMINA AT HIGH-TEMPERATURE

Polycrystalline Ca beta''-alumina was produced in a relatively gentle way by increasing stepwise the Ca content of (Na, Ca) beta''-alumina i n suitable mixtures of molten salts (Ca(NO3)(2) and CaCl2). When deter mining the conductivity of Ca beta''-alumina as a function of temperat ure by the four-probe technique, an irreversible decrease of the condu ctivity was observed in subsequent measurements if the temperature dur ing the first conductivity measurement was extended beyond 600 degrees C. Impedance measurements on such samples demonstrated that the condu ctivity decrease was due to an increase of the contribution of the gra in boundary resistivity to the total specific resistivity.