Grain boundary electronic structure related to the high-temperature creep resistance in polycrystalline Al 2O 3

Abstract

High-temperature creep deformation in polycrystalline Al 2O 3 with an average grain size of 1 μm is suppressed by the doping of 0.1 mol% SrO, LuO 1.5, SiO 2 or ZrO 2, while that is accelerated by MgO, CuO or TiO 2-doping at 1250°C. The difference in the creep resistance is considered to be originated from change in the grain boundary diffusion in Al 2O 3 due to the grain boundary segregation of the dopant cation. Change in the chemical bonding state in the cations-doped Al 2O 3 is examined by a first-principle molecular orbital calculations using DV-Xα method based on [Al 5O 21] 27− cluster model. A correlation is found between the creep resistance and product of net charges of aluminum and oxygen ions. The dopant effect on the high-temperature creep resistance in polycrystalline Al 2O 3 is in good agreement with the change in the ionic bonding strength between Al and O. The change in the chemical bonding strength can be explained in terms of both effects of cation-doping, which changes constitutions of molecular orbitals, and vacancy, which decreases the chemical bonding strength in Al 2O 3.