Electrical Conductivity and Defect Structure of Y2O3 as a Function of Water Vapor Pressure

The electrical conductivity of several sintered yttria ceramics with different levels of lower valent cation impurities was studied as a function of the partial pressure of water vapor (3 to 1600 Pa) at 500° to 1300°C in oxygen or air. At the higher temperatures yttria is a P‐type conductor, but at the lowest temperatures and highest water vapor pressures, an ionic contribution becomes significant. The p‐type conductivity decreases with increasing water vapor pressure. This is interpreted in terms of a model involving dissolution of hydrogen as interstitial protons and which counterbalance the effective charges of the lower valent impurities. At the higher water vapor pressures and lower impurity levels excess protons are probably compensated by interstitial hydroxide or oxygen ions. Indications of grain boundary segregation of impurities are reported.