DTA curves and XRD show that the polycrystalline Cd-stabilized Cs+-, Ag+-, Na+-, Li+-, NH4+-beta"-ferrites, Ca2+-, Sr2+-, Ba2+-, Mg2+-beta"-ferrites and Pb2+-, Cd2+-beta-ferrites, prepared by ion exchange on K+-beta"-ferrite decompose at different temperatures, 260-820-degrees-C, to alpha-Fe2O3 and CdFe2O4, or mixtures of hexaferrites and spinel-type ferrites, depending on the substituting ion. TG curves exhibited a weight loss, 1-4%, at 50-300-degrees-C due to dehydration and at higher temperatures due to the liberation of NH4+ ions and Na+-evaporation respectively.