High-temperature creep deformation in polycrystalline Al2O3 with an average grain size of 1μm was suppressed by the doping of 0.1mol%SrO, LuO1.5, SiO2 or ZrO2, while that was accelerated by MgO, CuO or TiO2-doping at 1250C. The difference in the creep resistance was considered to be originated from change in the grain boundary diffusion in Al2O3 due to the grain boundary segregation of the dopant cation. Change in the chemical bonding state in the cations-doped Al2O3 was examined by a first-principle molecular orbital calculations using DV-Xα method based on [Al5O21]27- cluster model. A correlation was found between the creep resistance and product of net charges of Al and O ions. The dopant effect on the high-temperature creep resistance in polycrystalline Al2O3 was in good agreement with the change in the ionic bonding strength between Al and O. The change in the chemical bonding strength could be explained in terms of both effects of cation-doping, which changed constitutions of molecular orbitals, and vacancy, which decreased the chemical bonding strength in Al2O3.

Grain Boundary Electronic Structure Related to the High-Temperature Creep Resistance in Polycrystalline Al2O3. H.Yoshida, Y.Ikuhara, T.Sakuma: Acta Materialia, 2002, 50[11], 2955-66