SYNTHESIS AND THERMAL-STABILITY OF POLYCRYSTALLINE NEW DIVALENT BETA''-FERRITES AND BETA-FERRITES PREPARED BY ION-EXCHANGE

Using ion-exchange chemistry the divalent cations Ba2+, Sr2+, Ca2+, Mg2+ Cd2+, Pb2+, Co2+, Zn2+, Mn2+, Fe2+, and Sn2+ have been substituted for K+ in polycrystalline CdO-stabilized K-β″-ferrite samples. Ba, Sr, Ca, Mg, Pb, and Cd ion exchange led to the synthesis of new materials, the divalent M2+ -β″-ferrites (M = Ba, Sr, Ca, Mg) and M2+ -β-ferrites (M = Cd, Pb), respectively, Co2+-diffusion resulted in the formation of a spinel-type Co-ferrite. In the case of Zn, Mn, Fe, and Sn the samples decomposed to α-Fe2O3. The thermal stability of the new divalent β″- and β-ferrites was studied either by high-temperature exchange reactions or by air annealing of the exchanged products. Ba- and Sr-β″-ferrites and Pb-β-ferrite converted to M-type hexagonal ferrites with the magnetoplumbite structure. Mg-β″-ferrite decomposed to a spinel-type Mg-ferrite, and Ca-β″-ferrite and Cd-β-ferrite decomposed to α-Fe2O3. Composition, lattice parameters, SEM photographs, and magnetic properties of the ferrites formed are given. The magnetic susceptibilities of the divalent β″- or β-ferrites have values between 0.63 and 1.14 × 10-4 emu/g · Oe at room temperature. © 1993 Academic Press. All rights reserved.