Yttrium segregation and YAG precipitation at surfaces of yttrium-doped alpha -Al sub 2 O sub 3

The study used AES and low-energy ion scattering on the surface of polycrystalline and single-crystal alpha -aluminas heated under vacuum to > 1500 degrees C. Extensive surface and intergranular precipitation of YAG occurred in a compact of 210 wt ppm Y content while apparent Y segregation to surface cation sites predominated in a second compact with 160 wt ppm Y content. The segregation enthalpy of Y to the Al sub 2 O sub 3 surface at 1700- 1900 degreeswas approximately - 44 kJ/mol with a max surface cation site occupancy ofapproximately 13%. 26 refs.