Formation of crystalline Ba-ferrite phase from α-Fe₂O₃ phase in amorphous precursor

The formation of crystalline Ba-ferrite/sapphire(001) films in an amorphous precursor during annealing was studied in a real-time synchrotron x-ray scattering experiment. From the x-ray integrated intensity and the surface morphology, we found that the crystalline Ba-ferrite phase was formed by solid phase transformation of the intermediate crystalline α-Fe₂O₃ phase, not by direct crystallization of the amorphous precursor. The solid phase transformation occurred at temperature above 500°C. The high crystallization temperature of the Ba-ferrite phase was attributed to the activation barrier for the diffusion of Ba ions into the α-Fe₂O₃ phase.