The diffusion of O in ultrafine-grained undoped monoclinic material was studied by using 18O as a tracer, and secondary ion mass spectroscopic profiling. Samples with a relative mass density of 97 to 99%, and average crystallite sizes of 80 or 300nm, were prepared from Zr by sputtering, inert-gas-condensation, oxidation, in situ consolidation of nanocrystalline oxide powder and pressureless sintering at 950 or 1050C in vacuum. The bulk and interface diffusivities were directly determined from the 18O diffusion profiles in the type-B and type-A regimes of interface diffusion. The diffusion of 18O in the interfaces of undoped nanocrystalline material was 103 to 104 times faster than in the bulk of the crystallites, at temperatures ranging from 450 to 950C. The diffusivities were independent of crystallite sizes ranging from 70 to 300nm. The activation energies of 2.29 and 1.95eV, for bulk and interface diffusion (figures 42 and 43), respectively, were considerably higher than the diffusion activation energies found in fast ion conductors such as Ca- or Y-stabilized zirconia.

Oxygen Diffusion in Ultrafine-Grained Monoclinic ZrO2. U.Brossmann, R.Würschum, U.Södervall, H.E.Schaefer: Journal of Applied Physics, 1999, 85[11], 7646-54

Figure 43

Interface Diffusivity of 18O in Nanocrystalline Monoclinic ZrO2