First-principles study of impurity segregation in zirconia, hafnia, and yttria-stabilized-zirconia grain boundaries

The impurity segregation behavior in symmetric tilt Σ5 (310)/[001] grain boundaries (GBs) of cubic ZrO2, HfO2, and yttria-stabilized ZrO2 (YSZ) were studied using first-principles calculations. The substitutional impurities, including divalent (Mg, Ca), trivalent (Al, Y), and tetravalent (Si, Ti) elements, were considered. It is found that divalent and trivalent impurities tend to segregate to a narrow region within 4 Å of the GB plane, while the tetravalent impurities have a much more scattered segregation profile extending 8–15 Å from the GB plane. For ZrO2 GB, the calculated grain boundary impurity enrichment factor for yttrium dopant is about 1.7, which is in good agreement with the experimental value of 1.9. For YSZ GB, there exist a strong GB segregation tendency for Mg, Ca, and Si, and a very weak segregation tendency for Ti in the YSZ GB, which is consistent with experimental findings.