High-temperature creep resistance in lanthanoid ion-doped polycrystalline Al2O3

High-temperature creep resistance in polycrystalline Al2O3 With 0.05 mol% lanthanoid oxides of Y, Sm, Eu, Tm or Lu has been examined by uniaxial compression creep testing at 1250 degrees C. The creep resistance is improved by the doping, and the dopant effect is dependent on the type of lanthanoid; the effect is in the order Sm < Tm < Eu < Y < Lu. Each dopant cation was found to segregate in grain boundaries and is likely to suppress grain-boundary diffusion. The change in chemical bonding state with doping was estimated by a first-principles molecular orbital calculation using the discrete variational (DV)-X-alpha method. A good correlation is found between the creep resistance and the net charge of the constituent ions. A change in the ionic bonding state in grain boundaries due to lanthanoid segregation must be the origin of the improved creep resistance in polycrystalline Al2O3.