Influence of Yttrium Doping on Grain Misorientation in Aluminum Oxide

Oversized dopant ions such as yttrium and lanthanum segregate to grain boundaries and reduce the tensile creep rate of α‐Al 2 O 3 by 2‐3 orders of magnitude. One explanation for this behavior is that the oversized segregants give rise to a “site‐blocking” effect for grain boundary diffusion. It has also been speculated that the dopant ions modify the grain boundary structure in alumina and reduce the creep rate by promoting the formation of special (e.g., coincidence site lattice (CSL)) grain boundaries. In order to test the latter hypothesis, we have used electron backscattered Kikuchi diffraction to characterize the misorientation and special grain boundary distribution for undoped and 1000‐ppm‐yttrium‐doped alumina. The results show that the grain boundary structure in alumina (as characterized by the frequency of selected CSLs and misorientation distribution) was not significantly changed by the addition of yttrium, indicating that creep retardation results mainly from site‐blocking.