Oxygen Isotope Transport Properties of Yttria‐Stabilized Zirconia (YSZ) in O 2 ‐ and H 2 O‐Containing Atmospheres

Oxygen isotope exchange experiments, H 2 18 O/H 2 16 O (”wet” anneals) and 18 O 2 / 16 O 2 (”dry” anneals), were performed on single crystal samples of yttria‐stabilized zirconia (YSZ) at a temperature of T  = 1073 K with subsequent determination of the oxygen isotope profiles in the solid by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Such experiments yielded oxygen tracer diffusion coefficients ( D *) and oxygen tracer surface exchange coefficients ( k *), from both the polished (smooth) and unpolished (rough) sides of single crystal samples, as a function of water partial pressure p H 2 O and oxygen partial pressure p O 2 . Isothermal values of D * were found to depend on neither p O 2 nor p H 2 O (nor surface roughness). Isothermal values of k *, in contrast, displayed a strong dependence on p O 2 or p H 2 O; k * wet was, in addition, 2–3 orders of magnitude higher than k * dry . Surprisingly, surface roughness had little effect on k * wet , whereas rough surfaces exhibited much higher k * dry values than smooth surfaces. Data for k * wet obtained as a function of temperature at p H 2 O = 18 mbar show a change in activation enthalpy at T  ≈ 973 K. The behavior of k * is discussed in terms of surface composition, surface area and surface reaction mechanisms.