Although the influence of yttrium on transport properties of 0~ alumina has been the object of many studies, the mechanisms by which this element acts have not yet been elucidated. The method of modification by yttrium of the microstructure of 0c polycrystalline alumina and the nature of the point defects created by this doping element were studied. The results obtained are discussed in relation to alumina transport properties and especially in relation with the effect of yttrium on the oxidation mechanism of alumina former alloys, taking into account the doping amount.

Yttrium-doped a-polycrystalline alumina was studied by microscopy observations and by extended X-ray absorption finestructure experiments. The latter results were compared to those obtained for a standard Yz03 powder and to theoretical spectra for YzO, and Y3AISOIZ calculated on the basis of crystallographic data. Most of the yttrium in the doped alumina is precipitated as a Y3Al5Olz phase. An observed threshold displacement involves a slight valence electron delocalization for the Y3+ ion.

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