The intergranular segregation of Y was investigated in a rhombohedral twin grain boundary of alumina. Deviation from the twin orientation was compensated by a periodic arrangement of intergranular dislocations. Transmission electron microscopy tools (CTEM and HREM, EDXS, EFTEM and EELS/ELNES) were used to characterize changes in the chemical and electronic environments along this twin. Within experimental limits, no Y was detected in the perfect twin parts. On the other hand, Y segregation occurred very locally in the dislocation cores on about 4 atomic planes perpendicularly to the grain boundary which, in fact, corresponded to the step height that was associated with the interfacial dislocations. By comparison with an undoped bicrystal, both the dislocation distribution and the Y segregation localization confirmed the influence of Y upon dislocation mobility. In Y-rich defects, high spatial resolution analysis of the energy loss near to edge structures of an absorption edge clarified the Al3+ cation environment; provided that the effects of local radiation damage were fully controlled.

Yttrium Segregation and Intergranular Defects in Alumina. D.Bouchet, S.Lartigue-Korinek, R.Molins, J.Thibault: Philosophical Magazine, 2006, 86[10], 1401-13