Evidence of Bilevel Solubility in the Bimodal Microstructure of TiO 2 ‐Doped Alumina

A phenomenon of bilevel solubility was observed in a TiO 2 ‐doped (2.0 wt%) alumina with bimodal microstructure sintered in N 2 . Surface contributions to dopant signals in individual grains were identified and removed, using a spatially resolved energy dispersive spectroscopy analysis. Two levels of solubility, 1.005 ± 0.166 and 0.504 ± 0.082 mol% of TiO 2 in Al 2 O 3 , were obtained for anisotropic and equiaxed grains, respectively. No grain size dependence of solubility was found, but segregation of SiO 2 to boundaries with the anisotropic grains was observed. This phenomenon was explained by the incorporation of Ti 3+ into the Al 2 O 3 lattice during the abnormal grain growth caused by SiO 2 liquid under a reducing atmosphere.