Cation self diffusion in nanocrystalline monoclinic zirconia

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It has been shown recently by Yoshida et al. (2004) that monoclinic zirconia exhibits superplasticity-like behaviour. However, in order to further understand the precise mechanism that controls the superplastic behaviour, it is essential to know the diffusivities of the cations in this special microstructure. Although there are several studies on cation diffusion in other polymorphs of zirconia, there are no reports on the diffusion in monoclinic zirconia since it is not possible to prepare dense samples by sintering above the monoclinic to tetragonal transformation temperature (1443 K). The objective of this project is to overcome these difficulties and to measure cation diffusion in monoclinic zirconia. Nearly fully dense monoclinic zirconia will be prepared by hot isostatically pressing the powder below the monoclinic to tetragonal transition temperature. In a recent study (Swaroop et al. 2005), it was demonstrated that hafnium and ytterbium can act as tracers for zirconium and yttrium, respectively. The tracer source will be deposited on monoclinic zirconia by pulsed laser deposition. After the diffusion experiment, secondary ion mass spectrometry will be used to obtain the tracer depth profiles wherefrom lattice and grain boundary cation diffusivities will be deduced.