Nitrogen defects from NH3 in rare-earth sesquioxides and ZrO2Electronic supplementary information (ESI) available: Supplementary figure. See DOI: 10.1039/c0dt01068e

Abstract

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 °C. The electrical conductivity in ammonia corresponded to that in H₂–Ar mixtures of similar pO₂. 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, NH^x_O, is proposed to describe this behavior. Conductivity measurements are interpreted in terms of nitrogen acceptors which are passivated by protons in the presence of H₂(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 NH^x_O concentration of 0.7 mol% was estimated from quantification of the nitrogen and hydrogen contents of a sample quenched in NH₃.