Hafnia (HfO2) ceramics containing 0.0, 5.0, and 10.0 vol % Al2O3, resp
ectively, were sintered, at 1600-degrees-C for various periods from 2-
24 h. Abnormal grain growth was found to occur in the Al2O3-containing
compositions. Hafnia containing 5.0 vol % Al2O3 exhibits an average g
rain size of almost double that of the Al2O3-free hafnia matrix, coupl
ed with a much wider grain-size distribution. The material containing
10.0 vol % Al2O3 shows a smaller average grain size than the compositi
on containing 5.0 vol % Al2O3. However, its average grain size is stil
l larger than that of the Al2O3-free hafnia on sintering at 1600-degre
es-C for more than 8 h. Microstructural characterization, carried out
using scanning electron microscopy (SEM) and transmission electron mic
roscopy (TEM) equipped with an energy dispersive analysis facility (ED
X), indicated that there existed a continuous segregant layer at the g
rain boundaries and grain junctions in the Al2O3-free hafnia. Hafnia e
xhibits a low solubility in the segregant layer phase which inhibits t
he growth of the hafnia grains. The Al2O3 particles act as a scavenger
for the silicon-rich glassy phase, damaging the continuous nature of
the boundary segregant layer and promoting grain growth in the Al2O3-d
oped hafnia ceramics. The microstructural development at the sintering
temperature is an overall result of the concurrent scavenger effect a
nd grain pinning by the Al2O3 particles.