The formation of barium hexaferrite from stoichiometric mixtures of BaCO_3, and Fe_2O_3, has been investigated by means of differential thermal analysis and thermogravimetry, x-ray diffraction, and transmission electron microscopy--energy dispersive spectrometry. The first step, which implies decarbonatation and monoferrite formation, includes the formation of various intermediate compounds, which are formed at contact points between BaCO_3, and Fe_2O_3 grains, and implies diffusion of both species. In the second step, barium hexafetrite is formed at interfaces between monoferrite and iron oxide mainly by diffusion of barium through the BF_6. lattice into the hematite lattice. This exothermic reaction process leads to nonagglomerated pseudohexagonal platelets with an average particle size very close to the one of the starting powder mixture (--1 mu m).
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