Zirconia‐Alumina Nanoparticles Prepared by Laser Evaporation: Powder Characterisation by TEM and 27Al MAS NMR

Contrary to predictions of the ZrO₂‐Al₂O₃ phase diagram powders of solid solutions of alumina in zirconia with up to 40 mol% Al₂O₃ are described in the recent literature. Up to now the interpretations of the microstructure of these materials are still inconsistent. Therefore we reinvestigated nanopowders prepared by laser evaporation starting from a mixture of 55 mol% ZrO₂ and 45 mol% Al₂O₃ by analytical high resolution transmission electron microscopy (TEM) and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR). The results reveal that in case of this preparation route a heterogeneous powder system is formed consisting dominantly of nanocrystallites of zirconia with an incorporation of, obviously, only a very small amount of alumina, and that the crystallites are surrounded by an amorphous layer of predominantly alumina. No indication was found that Al³⁺ ions occupy seven‐ or eight‐fold co‐ordinated sites of Zr⁴⁺ ions. A simple kinetic model for the formation of the nanoparticles' microstructure is given.