In situ crystallization of alpha-Fe2O3/alpha-Al2O3(0 0 0 1) thin films was studied in real-time synchrotron X-ray scattering experiments. We find the coexistence of alpha-Fe2O3 (hexagonal) and Fe3O4 (cubic) interfacial crystallites (similar to50-Angstrom-thick), well aligned [0.02degrees full-width at half-maximum (FWHM)] to the alpha-Al2O3[0001] direction, in the sputter-grown amorphous films. As the annealing temperature increases up to 750 degreesC, the cubic stacking of the Fe3O4 crystallites gradually changes to the hexagonal alpha-Fe2O3 stacking, together with the growth of the well-aligned (WA) (0.02 FWHM) grains from the alpha-Fe2O3 crystallites. In the meanwhile, heterogeneous nucleation starts to occur on the substrate at similar to600degreesC, resulting in the formation of misaligned (1.39degrees FWHM) alpha-Fe2O3 grains. Our study reveals that the interfacial crystallites act as a template for the growth of the WA alpha-Fe2O3 grains. (C) 2002 Published by Elsevier Science B.V.