Oxygen transfer in BIMEVOX materials

Two steps govern the oxygen transport in ceramic oxide ion conductors: (i) the oxygen exchange at the surface of the material and (ii) the oxygen diffusion through the material. The 18O/ 16O Isotope Exchange Depth Profile technique (IEDP) was applied to BIMEVOX materials to characterise the oxygen transfer in these ceramics. The isotope concentration profiles, obtained by secondary ion mass spectrometry (SIMS), revealed that the equilibrium exchange kinetics in BIMEVOXes under nominally dry oxygen are dominated by a relatively slow surface exchange step. This produces deep penetration profiles with very low isotopic concentrations close to the natural isotopic background. The oxygen surface exchange coefficient in these materials is of the same order of magnitude as in the classical oxide electrolytes, ceria gadolinia (CGO) and yttria-stabilised zirconia (YSZ). The transfer of oxygen from water is far easier, which makes the accurate determination of the true coefficient of exchange of the molecular oxygen for these materials more complicated and is probably dominated by the presence of residual water.