Abstract
The crystallographic relation between phase I and phase II of barium hexaaluminates, which were conventionally considered as the single compound “barium hexaaluminate (BaAl
12O
19),” was investigated using principally the electron diffraction method. Phase I (Ba
0.79Al
10.9O
17.14) was found to have β-alumina type structure with space group
P6
3
mmc
. On the other hand, phase II (Ba
2.34Al
21.0O
33.84) exhibited an
a√3 ×
a√3 superstructure, which is probably due to the ordering of excess Ba ions within BaO layers. Possible structure models of both phases are presented.