Corundum produced by dehydration of diaspore at 400 to 1000C was studied by X-ray diffraction and transmission electron microscopy. The broadening of X-ray diffraction peaks and the size of corundum twin domains were related to the dehydration temperature. At low dehydration temperatures (<450C) as well as at high temperatures (>700C) large twin domains were obtained which yielded sharp X-ray diffraction peaks for all reflections. Dehydration between 450 and 600C leads to twin domains smaller than 10nm. In this temperature range, significant peak broadening was observed, however, only for reflections, which structure factors were dominated by the Al sub-lattice and which were not common to both twin variants of corundum. The experimental results showed that X-ray diffraction peak broadening was only caused by fine twinning. Porosity in corundum as a reason for X-ray diffraction peak broadening was excluded: the lamellar pore system was well ordered in corundum produced at low temperatures, however narrow peaks were observed. The reasons for the development of twin domains with differing sizes at different dehydration temperatures were considered in detail.

Anisotropic X-Ray Diffraction Peak Broadening and Twinning in Diaspore-Derived Corundum. L.Löffler, W.Mader: Journal of the European Ceramic Society, 2005, 25[5], 639-48