Speaker
Description
Grain boundary mobility in ceramics can be extremely sensitive to segregating dopants or impurities. Using α-Al2O3 as a model system, we examined how Ca2+ and Fe dopants (with mixed Fe3+/Fe2+valencies) influence GB mobility. In Al2O3 doped with Ca below the solubility limit, Ca segregates to grain boundaries and increases the GB mobility, likely through charge-compensating oxygen vacancies. Dense Fe-doped Al2O3 (0.18–2.93 wt.% Fe), well below the solubility limit at 1600 °C (8.9 wt.%), was annealed in air or Ar. In air, grain growth was suppressed by solute drag: the GB mobility decreased with increasing Fe content, consistent with Fe3+ segregation at grain boundaries. In contrast, annealing in Ar increased the GB mobility and produced anisotropic grain growth, similar to Ca-doped Al2O3. X-ray photoelectron spectroscopy (bulk) and electron energy-loss spectroscopy (grain boundaries) show that lowering the oxygen partial pressure shifts Fe toward Fe2+ and increases the oxygen-vacancy concentration. White-line ratio analysis of the Fe L2,3 edges indicates that anisotropy arises from selective segregation of Fe3+/Fe2+ to specific GBs, which alters their mobility and promotes elongated grains. Fast-moving GBs are enriched in Fe2+ relative to slow-moving boundaries. These results demonstrate control of alumina grain size and morphology by tailoring dopant valence states and oxygen-vacancy concentrations.
| Professional Status of the Speaker | Senior Scientist |
|---|---|
| Invitation letter for visa | No |
| Interest in submitting a paper in a special issue of | No interest |
