Nitrogen defects from NH3 in rare-earth sesquioxides and ZrO2

Effects of nitrogen defects on the electrical properties of RE2O3 (RE = Nd, Gd, Er, Y) and ZrO2 have been investigated by equilibration in ammonia (NH3) atmospheres in the temperature range 1000-1200 degrees C. The electrical conductivity in ammonia corresponded to that in H-2-Ar mixtures of similar pO(2). However, upon replacing ammonia with an inert gas, the conductivity increases abruptly, typically one order of magnitude, before gradually returning to its equilibrium value. A defect model based on dissolution and dissociation of effectively neutral imide defects substituting oxide ions, NHOx, is proposed to describe this behavior. Conductivity measurements are interpreted in terms of nitrogen acceptors which are passivated by protons in the presence of H-2(g), and subsequently compensated by positive charge carriers in an inert atmosphere as out-diffusion of hydrogen leaves an effective acceptor, N'(O). In the case of Y2O3, a NHOx concentration of 0.7 mol% was estimated from quantification of the nitrogen and hydrogen contents of a sample quenched in NH3.