Oxygen diffusion in ultrafine grained monoclinic ZrO2

The diffusion of oxygen in ultrafine grained, undoped monoclinic ZrO2 was s tudied using O-18 as tracer and secondary ion mass spectroscopy profiling. Samples with a relative mass density of 97%-99% and average crystallite siz es of 80 or 300 nm were prepared from Zr by sputtering, inert-gas-condensat ion, oxidation, in situ consolidation of nanocrystalline (n-)ZrO2 powder an d subsequent pressureless sintering at 950 or 1050 degrees C in vacuum. Vol ume and interface diffusivities were directly determined from the O-18 diff usion profiles in n-ZrO2 in the type B and type A regime of interface diffu sion. The diffusion of O-18 in interfaces in undoped n-ZrO2 is 10(3)-10(4) times faster than in the bulk of the crystallites throughout the temperatur e range of 450 to 950 degrees C studied. These diffusivities are independen t of the crystallite size in the range of 70-300 nm. The activation energie s Q(V)=2.29 eV and Q(B)=1.95 eV for the volume (Q(V)) and interface diffusi on (Q(B)) are considerably higher than the diffusion activation energies fo und in the fast ion conductors Ca- or Y-stabilized ZrO2. Based on the prese nt data on oxygen diffusion in ZrO2, the cation and anion diffusivities of other binary oxides are discussed. (C) 1999 American Institute of Physics. [S0021-8979(99)02211-2].