Oxide/oxide composites in the system Cr2O3-Y2O3-Al2O3

Ceramic compacts in the systems Al2O3–Y2O3, Cr2O3–Y2O3 and Y3(CryAl1-y)5O12 (Cr-doped YAG) were prepared by solid state reaction in calcined co-precipitated powder mixtures of appropriate compositions. Various solid-solution phases were formed, e.g. Y3(Al1-xCrx)5O12, YAlyCr1-yO3 and Al2-xCrxO3. Composite materials in the pseudo-binary or ternary systems Al2O3–Y3Al5O12, Cr2O3–Y2O3 and Y3(Al1–xCrx)5O12–YAlyCr1–yO3–(AlzCr1−z)2O3 were obtained by hot-pressing appropriate powder precursors at 1600–1650°C for 1 h. The microstructure of the prepared materials was studied in a scanning electron microscope with element analysis facilities. X-ray diffraction was used to reveal the phases present and their lattice parameters. The chemical compatibility of these phases was investigated. The results are discussed with a special emphasis on the solubility of Cr in the YAG structure, and on the compatibility relationship between Cr-doped YAG and its neighbouring phases. A gel-coating process for preparing Al2O3–YAG composites with tailored microstructures is also described.