The kinetics of oxygen transport in 9.5 mol % single crystal yttria stabilised zirconia

Abstract

Isotope Exchange/Depth Profiling (IEDP) using secondary ion mass spectrometry (SIMS) has been used to determine the oxygen tracer diffusion and surface exchange coefficients of (100) oriented 9.5 mol % yttria stabilised zirconia single crystals. The activation enthalpy for oxygen tracer diffusion was found to be 0.9 eV in the temperature range 450–650 °C, and 0.8 eV in the temperature range 650–1100 °C. The activation enthalpy for the surface exchange reaction showed a marked transition from . The ionic conductivity of the samples was measured by ac impedance spectroscopy which gave an activation enthalpy of 1.1 eV. The Arrhenius plots of the ac impedance data showed some curvature due to vacancy trapping by (Y′ ZrV o ..) . defect associates at lower temperatures, and it was found that the binding enthalpy of these associates (0.26 eV) contributed significantly to the overall activation enthalpy. An intercomparison between the oxygen diffusivities obtained from the two techniques shows a high degree of correlation across the temperature range examined, however, we identify two temperature regimes where the correlation differs slightly. At higher temperatures ( T > 650 °c) the diffusivities are related by a Haven ratio of 0.48, whereas at lower temperatures ( T < 650 °c) the Haven ratio was found to be 0.33. To investigate this change in the Haven ratio, protonic transport was examined using ac impedance measurements in dry and wet atmospheres.