Formation of β-, β″- and β′′′-Alumina Type Ferrites in Rb₂O-Fe₂O₃ and Cs₂O-Fe₂O₃ Systems and

Abstract

The formation and ionic conductivity of β-, β′′- and β′′′-alumina type ferrites in the systems Rb₂O-Fe₂O₃ and Cs₂O-Fe₂O₃ were studied. Rb⁺-β-ferrite was formed by heating powder mixtures of Rb₂CO₃⋅(6-6.5) α-Fe₂O₃ above 1200°C, while Rb⁺-β′′-ferrite was synthesized together with the β phase below 1150°C. Rb⁺-β′′′-ferrite was obtained at 1400°C from Rb₂CO₃⋅10 α-Fe₂O₃. When the mixtures of Cs₂CO₃⋅(6-6.5) α-Fe₂O₃ and Cs₂CO₃⋅10 α-Fe₂O₃ were heated at 1000° and 1400°C, respectively, Cs⁺-β-and Cs⁺-β′′′-ferrites were formed. However, the β′′ phase was not obtained from Cs₂CO₃ and α-Fe₂O₃. Single phase Rb⁺-β′′-and Cs⁺-β′′-ferrites were obtained by heating the mixtures of Rb₂CO₃⋅3Fe₃O₄ and Cs₂CO₃⋅₃Fe₃O₄ at 950°-1000°C in air, respectively. The β′′-ferrites transformed to β phase at 1050°-1150°C. The lattice constants c_o of M⁺-β-, β′′- and β′′′-ferrites (M⁺: K⁺, Rb⁺ and Cs⁺) increased with increasing size of M⁺ ion. The β- and β′′-ferrites were mixed conductors of ion and electron. Rb⁺- and Cs⁺-β′′-ferrites have higher ionic conductivities than the respective β phases. The ionic conductivities are higher than those of other Rb⁺ and Cs⁺ conductors.