Electrical Conductivity of Y2O3 as a Function of Oxygen Partial Pressure in Wet and Dry Atmospheres

The electrical conductivity of polycrystalline Y 2 O 3 has been studied as a function of the partial pressure of oxygen (10 –14 to 10 5 Pa) at 900° to 1500°C in atmospheres saturated with water vapor at 12°C or dried with P 2 O 5 . Yttria is a p ‐conductor at high oxygen activities. The p ‐conductivity increases with increasing P O2 and decreases with increasing P H2O . At low oxygen activities the oxide is a mixed ionic/electronic conductor. The ionic conductivity is approximately independent of P O2 and increases with increasing P H2O . In the Y 2 O 3 samples, excesses of lower‐valent cation impurities (in the 10 to 100 mol‐ppm range) are the dominating negatively charged defects, and in the presence of water vapor they are compensated by interstitial protons. At high P H2O levels additional protons are probably compensated by interstitial oxygen ions. At high temperatures (±1100°C) and for high P O2 and low P H2O , the protons are no longer dominant, and the lower‐valent cations are mainly compensated by electron holes. The electrical conductivity exhibits hysteresis‐like effects which are interpreted in terms of segregation/desegregation of impurities at grain boundaries. The mobility of electron holes in yttria at 1500°C is estimated to be of the order of magnitude of 0.05 cm 2 . s –1 . V –1