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

High-temperature creep resistance in polycrystalline Al₂O₃with 0.05mol% lanthanoid oxides of Y, Sm, Eu, Tm or Lu has been examined by uniaxial compression creep testing at 1250°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_αmethod. 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.