Interpretation of the electric conductivity of ZrO$sub 2$ and HfO$sub 2$ at high temperature (1300$sup 0$C--1600$sup 0$C)

Ionic transport numbers have been measured for HfO$sub 2$ and ZrO$sub 2$ between 1300 and 1600$sup 0$C under partial oxygen pressures varying from 1 atm to 10$sup -10$ atm. The ionic and electronic contributions to the total conductivity are discussed. For HfO$sub 2$, Schottky disorder agrees with the results, while, in ZrO$sub 2$, impurities seem to play an important role. (auth)