Oxygen diffusion in ultrafine grained monoclinic ZrO2

The diffusion of oxygen in ultrafine grained, undoped monoclinic ZrO2 was studied using O18 as tracer and secondary ion mass spectroscopy profiling. Samples with a relative mass density of 97%–99% and average crystallite sizes of 80 or 300 nm were prepared from Zr by sputtering, inert-gas-condensation, oxidation, in situ consolidation of nanocrystalline (n-)ZrO2 powder and subsequent pressureless sintering at 950 or 1050 °C in vacuum. Volume and interface diffusivities were directly determined from the O18 diffusion profiles in n-ZrO2 in the type B and type A regime of interface diffusion. The diffusion of O18 in interfaces in undoped n-ZrO2 is 103–104 times faster than in the bulk of the crystallites throughout the temperature range of 450 to 950 °C studied. These diffusivities are independent of the crystallite size in the range of 70–300 nm. The activation energies QV=2.29 eV and QB=1.95 eV for the volume (QV) and interface diffusion (QB) are considerably higher than the diffusion activation energies found in the fast ion conductors Ca- or Y-stabilized ZrO2. Based on the present data on oxygen diffusion in ZrO2, the cation and anion diffusivities of other binary oxides are discussed.