Vacancy effect of dopant cation on the high-temperature creep resistance in polycrystalline Al2O3

High-temperature creep resistance in polycrystalline Al2O3 with 0.1 mol% oxides of YO1.5, ZrO2 or MgO has been examined by uniaxial compression creep testing at 1250 °C. The creep resistance is highly improved by the doping of Y or Zr even in the dopant level of 0.1 mol%, but is retarded by Mg doping. The dopant effect on the creep resistance cannot be explained in terms of, for example, ionic radius of the dopant cation or eutectic point in Al2O3-oxide of dopant cation system. Each dopant cation was found to segregate in grain boundaries, and is likely to influence grain boundary diffusion in Al2O3. The ionic bonding and the covalent bonding of Al–O are lowered by the introduction of VO′′ or VAl′′′ but the values of the net charge in Al and O are increased by the cations doping. The change in the value of Net Charge is correlated well with the high-temperature creep resistance in Al2O3 with cation doping. It is suggested that the ionicity in Al and O is an important factor to determine high-temperature creep resistance in polycrystalline Al2O3.