Abstract
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.
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